深冷轧制提高Al-Mg-Mn-Sc合金热稳定性及抑制第二相粗化的微观机制
The deep cryogenic rolling mechanism enhances the thermal stability and inhibits the coarsening of secondary phases in Al-Mg-Mn-Sc alloys

摘要：铝合金因其低密度和卓越的成形性能被广泛应用于车身轻量化制造。Al-Mg-Mn-Sc合金以其优异的力学性能和耐腐蚀性能，成为高性能全铝车身的重要选材。然而，不均匀变形会引起Al₃(Sc, Zr)相的聚集，进而在退火时易发生Al₃(Sc, Zr)相粗化，导致该合金热稳定性和耐蚀性下降。因此，如何避免Al₃(Sc, Zr)相粗化，并进一步提高Al-Mg-Mn-Sc合金的力学性能和热稳定性成为重要研究方向。本文研究发现，深冷轧制过程中剪切带和附加剪切应变促进晶粒和第二相的变形和破碎，实现了更显著的晶粒细化。在Al₃(Sc, Zr)相钉扎位错的基础上，结合深冷环境积累高密度位错的特点，使得深冷轧制样品的位错密度比室温轧制高出15%以上。此外，深冷轧制可促使Al₃(Sc, Zr)相均匀分布，进而抑制了退火过程中Sc、Zr元素短程扩散及其导致的Al₃(Sc, Zr)相粗化。深冷轧制样品中Al₃(Sc, Zr)相阻碍高温下的晶界迁移和位错攀移，保留了细晶组织和高密度位错，这是深冷轧制Al-Mg-Mn-Sc合金在退火过程中保持微观组织热稳定性和更高力学性能的关键。480℃退火1小时后，深冷轧制样品的再结晶程度仅为17.3%，比室温轧制样品低31%。深冷轧制Al-Mg-Mn-Sc合金在300℃退火1小时后抗拉强度仍可达到428 MPa，而断裂延伸率提高了2倍以上（18.4%），断裂延伸率和抗拉强度的乘积超过了7500 MPa∙%，高于类似研究中Al-Mg-Mn-Sc合金的力学性能。
Abstract: Aluminum alloys are widely used in vehicle lightweight manufacturing due to their low density and excellent formability. Al-Mg-Mn-Sc alloys, with their superior mechanical and corrosion resistance properties, are important materials for high-performance all-aluminum vehicles. However, uneven deformation can cause the aggregation of Al ₃ (Sc, Zr) phases, which can lead to the coarsening of Al ₃ (Sc, Zr) phases during annealing, resulting in a decrease in the thermal stability and corrosion resistance of the alloy. Therefore, how to avoid the coarsening of Al ₃ (Sc, Zr) phases and further improve the mechanical properties and thermal stability of Al-Mg-Mn-Sc alloys has become an important research direction. This study found that shear bands and additional shear strain during deep cold rolling promote the deformation and fragmentation of grains and second phases, achieving more significant grain refinement. Based on the pinning of dislocations by Al ₃ (Sc, Zr) phases and the characteristic of accumulating high-density dislocations in a deep cold environment, the dislocation density of deep cold rolled samples was more than 15% higher than that of room temperature rolled samples. Additionally, deep cold rolling promotes the uniform distribution of Al ₃ (Sc, Zr) phases, thereby inhibiting the short-range diffusion of Sc and Zr elements and the coarsening of Al ₃ (Sc, Zr) phases during annealing. The Al ₃ (Sc, Zr) phases in deep cold rolled samples hinder grain boundary migration and dislocation climb at high temperatures, preserving fine grain structure and high dislocation density, which is key to maintaining microstructural thermal stability and higher mechanical properties during annealing. After 1 hour of annealing at 480°C, the recrystallization degree of deep cold rolled samples was only 17.3%, which was 31% lower than that of room temperature rolled samples. After 1 hour of annealing at 300°C, the tensile strength of deep cold rolled Al-Mg-Mn-Sc alloys remained at 428 MPa, while the fracture elongation increased by more than 2 times (18.4%), and the product of fracture elongation and tensile strength exceeded 7500 MPa·%, which is higher than the mechanical properties of similar studies on Al-Mg-Mn-Sc alloys.

1 引言
1 Introduction

Al-Mg-Mn-Sc合金的力学性能和耐蚀性相比于常规的5xxx铝合金具有显著的优势，可更好地适应工业制造领域对轻质高性能铝合金材料的需求。进一步研究和开发Al-Mg-Mn-Sc合金，可推动轻量化、可持续化和材料科学技术的发展。添加Sc、Zr元素对力学性能、腐蚀性能等产生增益效果的根本原因是Sc、Zr元素在铝基体中形成了L1₂结构的Al₃(Sc, Zr)相。Sc、Zr元素合金化还影响Al-Mg-Mn合金的焊接性能，Al-Mg-Mn-Sc合金既可以作为具有良好焊接性能的焊接母材，还可以作为焊丝提高材料可焊性^[1]。焊缝中的Al₃Sc或Al₃(Sc, Zr)相成为形核点而细化晶粒^[2]，搅拌摩擦焊接Al-Mg-Mn-Sc合金的焊缝呈等轴晶形态，疲劳裂纹的萌生和扩展都被抑制，同时具有很好的力学性能和腐蚀性能^[3]。为了优化轧制后Al-Mg-Mn-Sc合金的综合力学性能，便于后续的成形加工，退火处理成为必要的后续工艺。适当的退火温度和时间既可以使材料内部的残余应力得到释放，有效减弱加工硬化导致的塑韧性降低，还可以提升材料的尺寸稳定性和耐蚀性，延长其使用寿命，同时避免晶粒过度长大和性能下降等负面影响。
The mechanical properties and corrosion resistance of Al-Mg-Mn-Sc alloys are significantly superior to those of conventional 5xxx aluminum alloys, better meeting the demands of the industrial manufacturing sector for lightweight and high-performance aluminum alloys. Further research and development of Al-Mg-Mn-Sc alloys can promote the development of lightweight, sustainable, and materials science and technology. The fundamental reason for the beneficial effects of adding Sc and Zr elements on mechanical and corrosion properties is the formation of Al(Sc, Zr) phases in the aluminum matrix with L12 structure. The alloying with Sc and Zr elements also affects the welding properties of Al-Mg-Mn alloys; Al-Mg-Mn-Sc alloys can serve as both welding substrates with good welding properties and welding wires to improve material weldability. The AlSc or Al(Sc, Zr) phases in the weld seam act as nucleation sites to refine the grain structure. The stir-friction-welded seam of Al-Mg-Mn-Sc alloys exhibits an equiaxed grain morphology, and the initiation and propagation of fatigue cracks are inhibited, while maintaining excellent mechanical and corrosion properties. To optimize the comprehensive mechanical properties of Al-Mg-Mn-Sc alloys after rolling and facilitate subsequent forming processing, annealing treatment becomes a necessary subsequent process. Appropriate annealing temperature and time can not only relieve internal residual stresses in the material, effectively mitigate the reduction in ductility and toughness caused by work hardening, but also enhance dimensional stability and corrosion resistance, extending the service life of the material. At the same time, it avoids the negative effects of excessive grain growth and property degradation.

Al-Mg-Mn-Sc合金与5xxx铝合金一样，主要的强化方式为加工硬化，因此为了制造更高性能的Al-Mg-Mn-Sc合金需进一步塑性变形。室温轧制不均匀变形会导致Al-Mg-Mn-Sc合金中的Al₃(Sc, Zr)相在局部聚集，导致Al₃(Sc, Zr)相在退火过程中粗化并削弱其对晶界和位错的钉扎效果，将导致Sc、Zr元素微合金化的效果大打折扣。在深冷环境中，一些金属材料表现出比室温条件下更优异的塑性，这一特殊的物理特性为深冷塑性成形技术的开发提供了坚实的理论基础和广阔的应用前景。近年来，随着对高性能金属材料需求的不断提升，国际上关于深冷轧制的研究逐渐增多^{[4, 5]}，许多学者致力于研究深冷变形过程中材料微观组织的演变、力学性能的变化以及深冷加工工艺的优化，这为高性能金属材料的制备提供了新的思路和方法，也推动了深冷塑性成形工艺的工业化应用进程。5xxx铝合金不具有时效强化能力，在热处理过程中难以形成细小弥散的强化相，因此通过其他方式提高5xxx铝合金的热稳定性具有重要价值，例如通过变形调控微观结构以实现热稳定性提高。深冷轧制这种促进均匀变形的加工方法或许可以使Al₃(Sc, Zr)相的分布更加均匀，这种微观组织差异性将对Al-Mg-Mn-Sc合金热稳定性产生影响。
Al-Mg-Mn-Sc alloys, like 5xxx aluminum alloys, mainly rely on work hardening for strengthening, so further plastic deformation is needed to produce higher-performance Al-Mg-Mn-Sc alloys. Room temperature uneven deformation can cause the Al@(0#)(Sc, Zr) phase to aggregate locally in Al-Mg-Mn-Sc alloys, leading to the coarsening of the Al@(1#)(Sc, Zr) phase during annealing and weakening its pinning effect on grain boundaries and dislocations, thereby diminishing the microalloying effect of Sc and Zr elements. In cryogenic environments, some metallic materials exhibit superior plasticity compared to room temperature conditions, providing a solid theoretical foundation and broad application prospects for the development of cryogenic plastic forming technology. Recently, with the increasing demand for high-performance metal materials, research on cryogenic rolling has been gradually increasing internationally. Many scholars have been studying the evolution of microstructure and changes in mechanical properties during cryogenic deformation and the optimization of cryogenic forming processes, providing new ideas and methods for the preparation of high-performance metal materials and promoting the industrial application of cryogenic plastic forming processes. 5xxx aluminum alloys do not have age-hardening capabilities and it is difficult to form fine and dispersed strengthening phases during heat treatment. Therefore, improving the thermal stability of 5xxx aluminum alloys through other means is of great value, such as regulating the microstructure through deformation to achieve thermal stability. Cryogenic rolling, a processing method that promotes uniform deformation, may make the distribution of the Al@(3#)(Sc, Zr) phase more uniform, and this microstructural difference will affect the thermal stability of Al-Mg-Mn-Sc alloys.

热稳定性通常指材料在高温环境下保持其组织结构和性能的能力。对铝合金材料而言，热稳定性可以通过退火过程中微观组织和力学性能变化评价。其中发生再结晶的比例越低，晶粒尺寸长大越缓慢，材料的热稳定性越好。从力学性能的角度，材料的强度、硬度等力学性能下降越小，则其热稳定性越好。在Al-Mg-Mn-Sc合金中，Al₃(Sc, Zr)弥散相可以抑制高温下的晶界迁移，对合金的微观组织和力学性能产生重要影响^[6]，但不均匀变形引起的Al₃(Sc, Zr)弥散相聚集，在高温下会进一步演化成Al₃(Sc, Zr)相粗化，这种现象会显著降低Al₃(Sc, Zr)弥散相在合金中的作用。Shen^[7]等研究了退火温度和时间对Al-6.15Mg-0.3Sc-0.15Zr合金再结晶行为的影响，结果显示在300℃和500℃退火时，合金的再结晶形核和晶粒长大动力不足，在550℃长时间保温，合金的织构才能由轧制织构向旋转立方织构转变。在550℃退火时Al₃(Sc, Zr)次生析出相发生粗化，随着保温时间延长，粗化程度逐渐显著，并且发生再结晶和晶粒长大。退火后强度的降低是因为位错密度减小，析出相粗化，晶粒长大等多因素共同导致。Al₃(Sc, Zr)相的形成不仅可以显著提高合金的再结晶温度，还能够提高合金的组织热稳定性。Tang等^[8]研究退火温度对Al-Mg-Mn-Sc-Zr合金力学性能的影响时发现，合金在300℃退火1小时获得最佳的力学性能，其抗拉强度、屈服强度和断裂延伸率分别为422.6 MPa、315.9 MPa和15.44%^[8]。Barkov等^[9]在研究中发现，Al-Mg-Mn-Zr-Sc合金在150℃退火后的屈服强度为365 MPa，抗拉强度为423 MPa，延伸率为8.3%。Lu等^[10]研究了Sc微合金化对Al-Mg-Mn合金在350℃退火后的力学性能，发现Al-Mg-Mn-Sc合金中由于Al₃(Sc, Zr)纳米弥散相对位错和晶界的钉扎作用，其屈服强度和抗拉强度在退火后仍然保持在318 MPa，437 MPa，并且延伸率达到14.8%。
Thermal stability typically refers to the ability of materials to maintain their microstructure and properties in high-temperature environments. For aluminum alloy materials, thermal stability can be evaluated by the changes in microstructure and mechanical properties during the annealing process. Among these, the lower the proportion of recrystallization, the slower the grain growth, the better the thermal stability of the material. From the perspective of mechanical properties, the smaller the decrease in properties such as strength and hardness, the better the thermal stability of the material. In Al-Mg-Mn-Sc alloys, the Al ₃ (Sc, Zr) dispersoids can inhibit grain boundary migration at high temperatures, significantly affecting the microstructure and mechanical properties ^[6] of the alloy, but uneven deformation-induced aggregation of Al ₃ (Sc, Zr) dispersoids at high temperatures further evolves into Al ₃ (Sc, Zr) phase coarsening, which significantly reduces the role of Al ₃ (Sc, Zr) dispersoids in the alloy. Shen ^[7] et al. studied the effects of annealing temperature and time on the recrystallization behavior of Al-6.15Mg-0.3Sc-0.15Zr alloy, showing that recrystallization nucleation and grain growth kinetics were insufficient at 300°C and 500°C annealing, and only at 550°C with long-term isothermal treatment did the texture of the alloy transform from a rolled texture to a rotated cubic texture. At 550°C annealing, the Al ₃ (Sc, Zr) secondary precipitates coarsen, and with extended isothermal time, the coarsening becomes increasingly significant, accompanied by recrystallization and grain growth. The reduction in strength after annealing is due to a decrease in dislocation density, coarsening of precipitates, and grain growth. The formation of Al ₃ (Sc, Zr) phase not only significantly increases the recrystallization temperature of the alloy but also enhances the organizational thermal stability of the alloy. Tang et al. ^[8] found that the alloy achieved optimal mechanical properties after 1 hour of annealing at 300°C, with tensile strength, yield strength, and fracture elongation of 422.6 MPa, 315.9 MPa, and 15.44%, respectively ^[8] . Barkov et al. ^[9] discovered that the yield strength and tensile strength of the Al-Mg-Mn-Zr-Sc alloy after annealing at 150°C were 365 MPa and 423 MPa, respectively, with an elongation of 8.3%. Lu et al. ^[10] studied the effect of Sc microalloying on the mechanical properties of Al-Mg-Mn alloys after annealing at 350°C, finding that in Al-Mg-Mn-Sc alloys, due to the pinning effect of Al ₃ (Sc, Zr) nanodisperoids on dislocations and grain boundaries, the yield strength and tensile strength remained at 318 MPa and 437 MPa, respectively, after annealing, with an elongation of 14.8%.

本文开展了深冷条件下Al-Mg-Mn-Sc合金的轧制工艺研究，深入研究了深冷轧制Al-Mg-Mn-Sc合金的微观组织演变和力学性能变化。以室温轧制为对照组，深入探讨了深冷轧制提高Al-Mg-Mn-Sc合金力学性能的微观机制。研究不同退火条件下，深冷轧制Al-Mg-Mn-Sc合金的热稳定性、微观组织演变和力学性能变化，对优化退火制度和提升合金的应用性能具有重要意义^[11]。聚焦该过程中Al-Mg-Mn-Sc合金力学性能的变化情况，理清深冷轧制抑制Al₃(Sc, Zr)相粗化，提升Al-Mg-Mn-Sc合金热稳定性的微观机制。
This paper conducted a study on the rolling process of Al-Mg-Mn-Sc alloys under cryogenic conditions, deeply investigating the microstructural evolution and mechanical property changes of cryogenically rolled Al-Mg-Mn-Sc alloys. Using room temperature rolling as a control group, it thoroughly explored the microscopic mechanisms by which cryogenic rolling improves the mechanical properties of Al-Mg-Mn-Sc alloys. The study of the thermal stability, microstructural evolution, and mechanical property changes of cryogenically rolled Al-Mg-Mn-Sc alloys under different annealing conditions is of great significance for optimizing the annealing process and enhancing the application performance of the alloy. The focus was on the changes in the mechanical properties of Al-Mg-Mn-Sc alloys during this process, elucidating the microscopic mechanisms by which cryogenic rolling suppresses the coarsening of Al(Sc, Zr) phases and enhances the thermal stability of Al-Mg-Mn-Sc alloys.

2 材料与试验方法
2 Materials and Test Methods

通过铸造获得Al-Mg-Mn-Sc合金，所用原料为纯铝（99.9%）和中间合金，中间合金包括Al-38Mg（wt.%）、Al-2Sc（wt.%）、Al-20Mn（wt.%）、Mg-25Zr（wt.%）。将纯铝和合适质量的中间合金加热至720℃~780℃并保温，熔融成铝水后加入精炼剂并充入氩气保护气氛。脱气除渣后，将铝液在720℃搅拌1小时，倒入预热好的铸铁模具中。Al-Mg-Mn-Sc合金铸锭首先在460℃的马弗炉中均匀化热处理6小时，随后使用铣床去除表面缺陷部分，此时铸锭厚度为30 mm，热轧前在460℃的马弗炉中保温2小时，热轧时每道次相对压下率小于20%，经历5次回炉保温和25道次轧制后，板材厚度减小至6 mm。所得板材再切成宽度90 mm，长度130 mm的板材，并在300℃的马弗炉中退火1小时。使用德国Spectro Blue全谱直读等离子体发射光谱仪测得Al-Mg-Mn-Sc合金预轧板（RM）中各元素成分占比，并列于表1中。
Through casting, Al-Mg-Mn-Sc alloys were obtained using pure aluminum (99.9%) and intermediate alloys, which included Al-38Mg (wt.%), Al-2Sc (wt.%), Al-20Mn (wt.%), and Mg-25Zr (wt.%). The pure aluminum and an appropriate amount of intermediate alloys were heated to 720℃~780℃ and kept at this temperature until melted into molten aluminum. After adding a refining agent and introducing argon gas for protection, de-gassing and slag removal were performed. The aluminum liquid was then stirred at 720℃ for 1 hour and poured into preheated iron molds. The Al-Mg-Mn-Sc alloy ingots were first uniformly heat-treated at 460℃ in a muffle furnace for 6 hours, followed by removal of surface defect parts using a milling machine. At this point, the ingot thickness was 30 mm, and it was then annealed at 460℃ in a muffle furnace for 2 hours before hot rolling. During hot rolling, the relative reduction per pass was less than 20%, and after 5 re-heating and 25 rolling passes, the plate thickness was reduced to 6 mm. The resulting plates were then cut into sheets of 90 mm width and 130 mm length. These sheets were annealed in a muffle furnace at 300℃ for 1 hour. The elemental composition of the pre-rolled Al-Mg-Mn-Sc alloy (RM) was measured using a German Spectro Blue full-spectrum direct reading plasma emission spectrometer, and the results are listed in Table 1.

表1 Al-Mg-Mn-xSc板材成分（质量百分数）
Table 1 Al-Mg-Mn-xSc Plate Composition (by Weight Percentage)

轧制实验在四辊轧机上进行，上下轧辊由同步电机驱动，轧机工作辊直径为200 mm，线速度为4 m/min，轧制过程无需润滑。本文研究了室温轧制（25℃，定义为RTR）和深冷轧制（-196℃，定义为CR）两种工艺，设定每道次压下量为当前板材厚度的10%左右，单道次最小压下量为0.2 mm，每种工艺条件下设置压下率为70%。
The rolling experiments were conducted on a four-high rolling mill, with the upper and lower rolls driven by synchronous motors. The working rolls had a diameter of 200 mm and a linear velocity of 4 m/min, and the rolling process did not require lubrication. This study investigated two processes: room temperature rolling (25°C, defined as RTR) and cryogenic rolling (-196°C, defined as CR). The reduction per pass was set to approximately 10% of the current sheet thickness, with a minimum reduction per pass of 0.2 mm. The reduction rate was set to 70% under each process condition.

室温轧制板材无需经历液氮预冷的过程。深冷轧制过程在-196℃的深冷条件下进行，这一温度是通过将板材浸泡在液氮中实现的。该方法可以有效模拟深冷环境，为研究深冷塑性变形提供相对稳定的温度条件。实际塑性变形过程中，由于材料内部的塑性部分转化为内能，可能导致局部温度上升（绝热温升效应），但是由于轧制过程变形发生迅速，绝热温升效应更不明显，且在不同温度轧制时的变化较小，因此本研究中忽略了绝对温升效应的影响。深冷轧制的具体操作步骤为：首先将待轧制的板材置于盛有液氮的保温箱中预冷30分钟，确保板材充分冷却至液氮温度。在随后的轧制过程中，每道次轧制前，将板材重新放置于液氮箱中继续冷却5分钟，以保证样品与液氮温度相同，随后再次进行轧制塑性变形。
Thermal rolling sheets do not require liquid nitrogen pre-cooling. The deep cryogenic rolling process is carried out at -196°C, which is achieved by immersing the sheets in liquid nitrogen. This method can effectively simulate deep cryogenic conditions, providing relatively stable temperature conditions for the study of deep cryogenic plastic deformation. During actual plastic deformation, due to the conversion of plastic deformation energy into internal energy within the material, there may be a local temperature rise (adiabatic temperature rise effect), but due to the rapid deformation during the rolling process, the adiabatic temperature rise effect is less noticeable, and the changes are minimal when rolling at different temperatures. Therefore, the adiabatic temperature rise effect was ignored in this study. The specific operational steps for deep cryogenic rolling are as follows: first, place the sheets to be rolled in an insulated box filled with liquid nitrogen for 30 minutes to ensure they are fully cooled to the liquid nitrogen temperature. During the subsequent rolling process, immerse the sheets in the liquid nitrogen box for an additional 5 minutes before each pass to ensure that the sample is at the same temperature as the liquid nitrogen, and then proceed with plastic deformation rolling.

进一步探讨退火处理如何影响材料的力学性能及其微观组织的热稳定性。首先，对轧制Al-Mg-Mn-Sc合金进行了非等温退火，温度为100℃至500℃，升温速度为50℃/小时，每25℃取样一次并测量合金的硬度。最后，对轧制Al-Mg-Mn-Sc合金进行了更高温度和更长时间的退火处理，在200℃~450℃范围内不同温度进行了1小时的等温退火处理。另外，在300℃下进行了5小时、10小时、100小时和500小时的退火实验。
Further investigation into how annealing affects the mechanical properties of materials and the thermal stability of their microstructural organization. First, a non-isothermal annealing was conducted on rolled Al-Mg-Mn-Sc alloy at temperatures ranging from 100℃ to 500℃ with a heating rate of 50℃/hour, and samples were taken and hardness measurements were made every 25℃. Finally, a higher temperature and longer annealing treatment was performed on the rolled Al-Mg-Mn-Sc alloy, with isothermal annealing at different temperatures in the range of 200℃ to 450℃ for 1 hour each. Additionally, annealing experiments were conducted at 300℃ for 5 hours, 10 hours, 100 hours, and 500 hours.

显微硬度在转塔式硬度计上测试，载荷为300 gf（约2.94 N），保荷时间为15 s。每个试样在抛光后重复测试显微硬度5次。室温和深冷拉伸实验参照GB/T 33227-2016标准，在岛津AGS-X 10 kN万能试验机上进行，实验过程可通过控制面板或微机操控。拉伸实验应变速率为1×10^-3 s^-1。实验采用狗骨头状拉伸试样，平行段长度为13 mm，宽度为3 mm，厚度为板材实际厚度。另外，对轧制后的Al-Mg-Mn-Sc合金在150℃、200℃、250℃和300℃下的高温力学性能进行了测试。
Microhardness was tested on a turret hardness tester with a load of 300 gf (approximately 2.94 N) and a holding time of 15 s. Each sample was tested for microhardness five times after polishing. Room temperature and deep cryogenic tensile tests were conducted according to the GB/T 33227-2016 standard using an Island 津 AGS-X 10 kN universal testing machine, with the experimental process controllable via the control panel or microcomputer. The tensile test strain rate was 1×10^-2 s^-1. Dog bone-shaped tensile specimens were used, with a gauge length of 13 mm, width of 3 mm, and thickness equal to the actual thickness of the sheet. Additionally, the high-temperature mechanical properties of the rolled Al-Mg-Mn-Sc alloy at 150℃, 200℃, 250℃, and 300℃ were tested.

对样品的RD-ND面进行机械抛光和氩离子抛光，氩离子抛光使用日立IM4000 Plus氩离子研磨系统，随后在配有Oxford symmetry S3探头的ZEISS Gemini 300扫描电镜上进行信号采集。合金样品首先通过机械研磨减薄至100 μm以下，然后使用裁切器裁剪成直径3 mm的小圆片。最后在-30℃的硝酸和甲醇溶液（体积比1:4）中进行双射流电解抛光减薄，使样品上产生可以被电子透过的薄区。随后使用场发射透射电子显微镜（TEM）Tecnai G2 F20观察显微组织。
The RD-ND face of the sample was mechanically polished and argon ion polished. The argon ion polishing was performed using the Hitachi IM4000 Plus argon ion polishing system, followed by signal acquisition on a Zeiss Gemini 300 scanning electron microscope equipped with an Oxford Symmetry S3 probe. The alloy sample was first mechanically thinned to below 100 μm and then cut into 3 mm diameter circular discs using a cutter. Finally, double-jet electrolytic polishing was carried out in a nitric acid and methanol solution (volume ratio 1:4) at -30℃, creating a thin region in the sample that is electron-transmissive. The microstructure was then observed using a field-emission transmission electron microscope (TEM) Tecnai G2 F20.

3 实验结果
3 Experimental Results

3.1 轧制及退火Al-Mg-Mn-Sc合金的力学性能
3.1 Mechanical Properties of Al-Mg-Mn-Sc Alloy after Rolling and Annealing

Al-Mg-Mn-Sc合金预轧板在经过塑性变形后，强度显著提高，其沿RD方向的力学性能如图1（a）所示。拉伸曲线上的锯齿状波动是PLC效应引起的^[12]，其根本原因在于溶质Mg原子对位错的钉扎作用。溶质原子在晶格中钉扎位错，导致位错运动受阻，进而使应力逐渐增大而应变不增加。当应力增加到一定阈值时，位错会突然突破溶质原子的束缚，重新开始滑移，瞬间的解锁导致应力突然下降，从而在应力应变曲线上形成锯齿状的波动。这种现象反映了位错运动的间歇性特点，是PLC效应的典型表现。Al-Mg-Mn-Sc合金预轧板的屈服强度和极限抗拉强度分别达到234 MPa、352 MPa。轧制变形70%时，深冷轧制Al-Mg-Mn-Sc合金板材的屈服强度达到436 MPa，极限抗拉强度为459 MPa，而室温轧制样品的屈服强度和极限抗拉强度则分别为410 MPa和439 MPa，两种样品的断裂延伸率均达到6%以上。如图1（b）所示，轧制前Al-Mg-Mn-Sc合金硬度为100.9 HV。深冷轧制Al-Mg-Mn-Sc合金的显微硬度达到141.4 HV，高于室温轧制样品（136.1 HV），表明深冷环境下的轧制有助于显著提高合金的硬度。
The strength of the Al-Mg-Mn-Sc alloy pre-pressed sheet significantly increases after plastic deformation, as shown in the mechanical properties along the RD direction in Figure 1(a). The sawtooth fluctuations in the tensile curve are caused by the PLC effect ^[12] , which is fundamentally due to the pinning effect of solute Mg atoms on dislocations. Solute atoms pin dislocations in the crystal lattice, causing dislocation motion to be impeded, which results in stress gradually increasing while strain does not increase. When the stress reaches a certain threshold, dislocations suddenly break free from the solute atoms and resume glide, the sudden release leading to a sudden drop in stress, thus forming sawtooth fluctuations in the stress-strain curve. This phenomenon reflects the intermittent nature of dislocation motion and is a typical manifestation of the PLC effect. The yield strength and ultimate tensile strength of the Al-Mg-Mn-Sc alloy pre-pressed sheet reach 234 MPa and 352 MPa, respectively. When the rolling deformation reaches 70%, the yield strength of the deep cryogenic rolled Al-Mg-Mn-Sc alloy sheet reaches 436 MPa, with an ultimate tensile strength of 459 MPa. In contrast, the yield strength and ultimate tensile strength of the room temperature rolled samples are 410 MPa and 439 MPa, respectively, with both samples exhibiting a fracture elongation rate of over 6%. As shown in Figure 1(b), the hardness of the Al-Mg-Mn-Sc alloy before rolling is 100.9 HV. The microhardness of the deep cryogenic rolled Al-Mg-Mn-Sc alloy reaches 141.4 HV, which is higher than that of the room temperature rolled sample (136.1 HV), indicating that rolling under deep cryogenic conditions significantly enhances the alloy's hardness.

研究退火温度对合金力学性能的影响，设定退火时间为1小时，退火温度从200℃开始，每间隔50℃设置一组，最高温度为450℃，通过退火后的室温单轴拉伸试验研究其力学性能变化。如图1（c-d）所示，在200℃~450℃区间内，退火温度对Al-Mg-Mn-Sc合金力学性能的影响是显著的，随着退火温度的不断提高，断裂延伸率从13.7%提高至20.7%，抗拉强度和屈服强度不断降低，但深冷轧制样品的强度始终高于室温轧制样品。200℃退火1小时后，深冷轧制Al-Mg-Mn-Sc合金屈服强度下降为346 MPa，但保持较高的抗拉强度（435 MPa），此时断裂延伸率达到14.2%。在300℃退火后，深冷轧制和室温轧制Al-Mg-Mn-Sc合金的屈服强度分别为324 MPa和297 MPa，保持抗拉强度在428 MPa和391 MPa。当退火温度升高到450℃时，深冷轧制Al-Mg-Mn-Sc抗拉强度仍可以达到396 MPa，但此时屈服强度降低至259 MPa。如图1（c-d）所示，深冷轧制Al-Mg-Mn-Sc合金的屈服强度始终大于室温轧制样品，延伸率差别较小。
To study the effect of annealing temperature on the mechanical properties of an alloy, the annealing time was set to 1 hour, with annealing temperatures starting at 200°C and increasing by 50°C for each group, up to a maximum of 450°C. The mechanical property changes were investigated through room temperature uniaxial tensile tests after annealing. As shown in Figure 1(c-d), the effect of annealing temperature on the mechanical properties of the Al-Mg-Mn-Sc alloy is significant in the range of 200°C to 450°C. As the annealing temperature increases, the fracture elongation increases from 13.7% to 20.7%, while the tensile strength and yield strength decrease continuously. However, the yield strength of the deep-drawn samples remains higher than that of the room temperature rolled samples. After annealing at 200°C for 1 hour, the yield strength of the deep-drawn Al-Mg-Mn-Sc alloy decreases to 346 MPa, but it maintains a high tensile strength of 435 MPa, with a fracture elongation of 14.2%. After annealing at 300°C, the yield strength of the deep-drawn and room temperature rolled Al-Mg-Mn-Sc alloys is 324 MPa and 297 MPa, respectively, while their tensile strengths remain at 428 MPa and 391 MPa, respectively. When the annealing temperature is increased to 450°C, the tensile strength of the deep-drawn Al-Mg-Mn-Sc alloy can still reach 396 MPa, but the yield strength decreases to 259 MPa. As shown in Figure 1(c-d), the yield strength of the deep-drawn Al-Mg-Mn-Sc alloy is always higher than that of the room temperature rolled samples, with only a small difference in elongation.

图1 轧制Al-Mg-Mn-Sc合金的（a）工程应力-应变曲线，（b）显微硬度柱状图，（c-d）室温轧制及深冷轧制Al-Mg-Mn-Sc合金在不同温度退火1小时样品的应力应变曲线；
Figure 1 (a) Engineering stress-strain curve of rolled Al-Mg-Mn-Sc alloy, (b) Microhardness bar chart, (c-d) Stress-strain curves of room temperature rolled and deep cryogenic rolled Al-Mg-Mn-Sc alloy samples annealed for 1 hour at different temperatures

通过研究非等温退火过程中Al-Mg-Mn-Sc合金的硬度变化可以初步确定发生回复和再结晶的温度区间^[13]。如图2所示，深冷轧制Al-Mg-Mn-Sc合金的硬度随着温度的升高而减小，但在整个退火过程中，硬度下降平缓，没有出现快速下降的阶段。退火前样品的硬度超过140 HV，升温到500℃时，深冷轧制Al-Mg-Mn-Sc的硬度仍然可以保持97.8 HV。但室温轧制样品在450℃之后出现了更显著的硬度下降，在500℃时硬度下降至85.0 HV。
By studying the hardness changes of Al-Mg-Mn-Sc alloys during non-isothermal annealing, the temperature range for recrystallization and recovery can be preliminarily determined. As shown in Figure 2, the hardness of deep-rolled Al-Mg-Mn-Sc alloys decreases with increasing temperature, but the decrease is gradual throughout the annealing process, without any rapid drop. Before annealing, the hardness of the samples exceeded 140 HV. Even when heated to 500°C, the hardness of the deep-rolled Al-Mg-Mn-Sc alloys remained at 97.8 HV. However, for room-temperature rolled samples, a more significant hardness drop occurred after 450°C, with the hardness decreasing to 85.0 HV at 500°C.

Al-Mg-Mn-Sc合金的软化发生得很慢，深冷轧制样品在整个退火过程中硬度下降幅度仅为30.8%。室温轧制样品的硬度从136.1 HV下降至85.0 HV，下降幅度达到37.5%。回复过程中硬度是缓慢下降的，而再结晶会导致硬度显著减小^[13]，非等温退火实验初步确定了深冷轧制和室温轧制Al-Mg-Mn-Sc合金发生回复和晶粒长大的温度区间，并在图2中以相应颜色的色块标出。
The softening of the Al-Mg-Mn-Sc alloy occurs slowly, with the hardness of the deep cryogenic cold-rolled samples decreasing by only 30.8% throughout the annealing process. The hardness of the room temperature cold-rolled samples decreased from 136.1 HV to 85.0 HV, a reduction of 37.5%. During the recrystallization process, the hardness decreases slowly, while recrystallization leads to a significant reduction in hardness ^[13] . Isothermal annealing experiments preliminarily determined the temperature ranges for recrystallization and grain growth in the deep cryogenic cold-rolled and room temperature cold-rolled Al-Mg-Mn-Sc alloys, which are indicated in Figure 2 with corresponding colored blocks.

图2 非等温退火过程中Al-Mg-Mn-Sc合金的硬度变化
Figure 2: Hardness Change of Al-Mg-Mn-Sc Alloy during Non-isothermal Annealing Process

为了研究车身铝结构在遭遇无意识火灾时可承受的应力情况，对轧制后的Al-Mg-Mn-Sc合金的高温力学性能进行测试。高温力学性能和热稳定性密切相关，热稳定性直接影响材料在高温条件下的强度、蠕变抗性以及使用寿命。通过细化晶粒、添加热稳定性良好的第二相等是优化高温力学性能的关键手段。与5xxx铝合金中的β相不同，Al₃(Sc, Zr)强化相为L1₂稳定结构，对合金在高温下的力学性能和微观组织都有重要影响。图3是Al-Mg-Mn-Sc合金在不同温度拉伸的应力应变曲线和力学性能结果。
To study the stress conditions that vehicle body aluminum structures can withstand during unconscious fires, the high-temperature mechanical properties of the rolled Al-Mg-Mn-Sc alloy were tested. High-temperature mechanical properties and thermal stability are closely related, with thermal stability directly affecting the material's strength, creep resistance, and service life at high temperatures. Grain refinement and adding second phases with good thermal stability are key means to optimize high-temperature mechanical properties. Unlike the β phase in 5xxx aluminum alloys, the Al ₃ (Sc, Zr) strengthening phase forms an L1 ₂ stable structure, which has a significant impact on the alloy's mechanical properties and microstructure at high temperatures. Figure 3 shows the stress-strain curves and mechanical property results of the Al-Mg-Mn-Sc alloy under tensile testing at different temperatures.

图3（a）展示了在150℃拉伸的实验结果，深冷轧制的Al-Mg-Mn-Sc合金具有更高的强度，其屈服强度达到357 MPa，抗拉强度达到370 MPa，此时断裂延伸率达到23%。室温轧制样品的抗拉强度仅329 MPa，断裂延伸率为27%。如图3（b）所示，将拉伸温度提高到200℃，Al-Mg-Mn-Sc合金的强度有明显降低。深冷轧制Al-Mg-Mn-Sc合金的强度明显高于室温轧制样品，其屈服强度达到283 MPa。室温轧制Al-Mg-Mn-Sc合金的屈服强度则为234 MPa。在250℃拉伸的应力应变曲线如图3（c）所示，温度提高50℃，合金的强度下降十分显著，样品的极限抗拉强度和屈服强度接近。深冷轧制Al-Mg-Mn-Sc合金的屈服强度降低至166 MPa，室温轧制样品降低至133 MPa，此时室温轧制Al-Mg-Mn-Sc合金的断裂延伸率达到80%，深冷轧制样品的断裂延伸率达到83%。300℃拉伸得到的应力应变曲线如图3（d）所示。室温轧制Al-Mg-Mn-Sc合金的屈服强度仅为102 MPa，断裂延伸率达到了136%，深冷轧制样品的断裂延伸率为138%，并且屈服强度达到119 MPa，比室温轧制样品高出20%。
Figure 3(a) shows the experimental results of tensile testing at 150℃, where the Al-Mg-Mn-Sc alloy subjected to deep cryogenic rolling has higher strength, with a yield strength of 357 MPa and tensile strength of 370 MPa, and a fracture elongation of 23%. The tensile strength of the room temperature rolled sample is only 329 MPa, with a fracture elongation of 27%. As shown in Figure 3(b), when the tensile temperature is increased to 200℃, the strength of the Al-Mg-Mn-Sc alloy decreases significantly. The deep cryogenic rolled Al-Mg-Mn-Sc alloy has significantly higher strength, with a yield strength of 283 MPa, while the yield strength of the room temperature rolled sample is 234 MPa. The stress-strain curve at 250℃ tensile testing is shown in Figure 3(c), where the strength of the alloy decreases significantly with a 50℃ increase in temperature, and the ultimate tensile strength and yield strength of the samples are close. The yield strength of the deep cryogenic rolled Al-Mg-Mn-Sc alloy decreases to 166 MPa, while that of the room temperature rolled sample decreases to 133 MPa. At this point, the fracture elongation of the room temperature rolled Al-Mg-Mn-Sc alloy reaches 80%, while that of the deep cryogenic rolled sample reaches 83%. The stress-strain curve at 300℃ tensile testing is shown in Figure 3(d), where the yield strength of the room temperature rolled Al-Mg-Mn-Sc alloy is only 102 MPa, with a fracture elongation of 136%, while the fracture elongation of the deep cryogenic rolled sample is 138%, and the yield strength is 119 MPa, which is 20% higher than that of the room temperature rolled sample.

图3 150℃~300℃拉伸Al-Mg-Mn-Sc合金的应力应变曲线：（a）150℃，（b）200℃，（c）250℃，（d）300℃
Figure 3 Stress-strain curves of Al-Mg-Mn-Sc alloy stretched at 150℃~300℃: (a) 150℃, (b) 200℃, (c) 250℃, (d) 300℃

3.2 轧制及退火过程Al-Mg-Mn-Sc合金微观组织演变
3.2 Rolling and Annealing Process Microstructural Evolution of Al-Mg-Mn-Sc Alloy

对轧制后的Al-Mg-Mn-Sc合金样品进行微观组织分析，深冷轧制和室温轧制样品的EBSD结果如图4所示。两个样品中的晶粒都沿着轧制方向被拉长并且有明显的剪切带，密集分布的剪切带几乎贯穿整个EBSD采集区域，且剪切带的连续性较高、长度较长。深冷轧制和室温轧制样品的面积加权平均晶粒尺寸分别为2.8 μm和4.0 μm。对比KAM图发现，深冷轧制和室温轧制样品都存在较高的应力，二者的平均KAM取向差分别是2.95×10^-2 rad和2.53×10^-2 rad。EBSD的信号采集步长为0.27 μm，根据如下公式可以计算轧制Al-Mg-Mn-Sc合金中的几何必要位错密度：
Microstructure analysis was conducted on Al-Mg-Mn-Sc alloy samples after rolling. The EBSD results for the deep cryogenic rolling and room temperature rolling samples are shown in Figure 4. In both samples, grains are elongated along the rolling direction with distinct shear bands that densely populate the entire EBSD acquisition area, and the continuity and length of the shear bands are high. The area-weighted average grain size for the deep cryogenic rolling and room temperature rolling samples are 2.8 μm and 4.0 μm, respectively. Comparison of KAM maps reveals that both samples exhibit high stress, with average KAM orientation differences of 2.95×10^ ^-2 rad and 2.53×10^ ^-2 rad, respectively. The EBSD signal acquisition step size is 0.27 μm, and the geometric necessary dislocation density in the rolled Al-Mg-Mn-Sc alloy can be calculated using the following formula:

  (1)

计算可得深冷轧制和室温轧制Al-Mg-Mn-Sc合金的位错密度分别为7.64×10¹⁴ m^-2，6.55×10¹⁴ m^-2。
The dislocation density for deep cryogenic rolling and room temperature rolling of Al-Mg-Mn-Sc alloy can be calculated as 7.64×10^ ¹⁴ m^-1# and 6.55×10^ ¹⁴ m^-3# respectively.

轧制变形过程中还会形成大量密集的剪切带，剪切带是塑性变形过程中应变集中的结果，剪切带通常沿着最小临界分切应力的方向。剪切带是局部高应变区域，更容易促进晶粒破碎和分裂，从而实现晶粒细化^[14]。图4（e-f）展示了基于EBSD实验结果的带对比（BC）图，比IPF图更清晰地反映了剪切带在Al-Mg-Mn-Sc合金中的分布。Al-Mg-Mn-Sc合金中剪切带数量较多，几乎分布在整个EBSD采集区域。相对于室温轧制，深冷轧制Al-Mg-Mn-Sc合金中剪切带的密度更大，分布更均匀，从而获得更显著的晶粒细化效果。
A large number of dense shear bands are also formed during the rolling deformation process, which are the result of strain concentration during plastic deformation and typically align with the direction of the minimum critical shear stress. Shear bands are regions of localized high strain, facilitating grain cracking and splitting to achieve grain refinement ^[14] . Figure 4(e-f) shows the band contrast (BC) map based on EBSD experimental results, which more clearly reflects the distribution of shear bands in the Al-Mg-Mn-Sc alloy compared to the IPF map. There are a large number of shear bands in the Al-Mg-Mn-Sc alloy, almost distributed throughout the entire EBSD acquisition area. Compared to room temperature rolling, deep cryogenic rolling of the Al-Mg-Mn-Sc alloy results in a higher density and more uniform distribution of shear bands, leading to more significant grain refinement.

深冷轧制和室温轧制样品的区别之一在于深冷轧制样品中短剪切带的数量更多，分布更加广泛。深冷轧制样品中剪切带的分布更加均匀，这可以归因于深冷抑制了局部位错重排且促进主滑移方向的变形，进而促使变形均匀发生。随着变形继续发生，几乎每个区域同时达到应变集中的临界条件，从而形成均匀分布的剪切带。Al-Mg-Mn-Sc合金中产生大量的剪切带的原因则是Sc元素合金化引入的Al₃(Sc, Zr)相极大地增加了合金中的位错密度，位错塞积导致了局部应力集中，进而形成密集分布的剪切带。另外，深冷轧制Al-Mg-Mn-Sc合金中的晶粒尺寸更小，晶界数量更多，而晶界阻碍了位错的自由滑移，也是导致剪切带数量更多的原因之一。图4（f）所示的室温轧制样品中由于不均匀变形而形成了交叉剪切带，这种交叉剪切带不仅阻碍了变形的进一步发生，也容易产生更严重的应变集中，可能成为断裂裂纹的萌生点。此外，由于合金中的第二相在滑移受阻时，易随着剪切带流动，这种室温轧制样品中的交叉剪切带便成为Al₃(Sc, Zr)相聚集的区域，在退火等热处理过程中，Sc、Zr元素的短程扩散更容易发生，Al₃(Sc, Zr)相粗化所需的能量势垒也就更低。而深冷轧制过程中均匀变形可以促使第二相颗粒均匀分布在基体中，减少局部区域因应力过高导致的相粒团聚或粗化。均匀变形在材料加工中起着至关重要的作用，不仅减少了局部应力集中的发生，还有助于位错均匀滑移和积累。深冷轧制可提高变形均匀性的证据在复合板材轧制过程中尤为明显，Song等^[15]研究累积叠轧的AA1050/AA5052复合板时发现，由于两种铝合金的硬度等差异，累积叠轧过程中会发生层间颈缩，在累积叠轧后进行深冷轧制可以显著改善层间颈缩和不均匀分布剪切带导致的力学性能下降。Liu等^[16]在研究Cu/Nb复合板时发现，室温轧制会产生不平整的高能界面，而深冷轧制样品界面平滑，这种平滑结构可提高合金的热稳定性和力学性能。
One of the differences between deep cryogenic cold-worked and room temperature cold-worked samples is that the deep cryogenic cold-worked samples have more and more evenly distributed shear bands. The distribution of shear bands in deep cryogenic cold-worked samples is more uniform, which can be attributed to the deep cryogenic process suppressing local dislocation rearrangement and promoting deformation along the main slip direction, thereby facilitating uniform deformation. As deformation continues, almost every region reaches the critical condition for strain concentration simultaneously, leading to the formation of uniformly distributed shear bands. The large number of shear bands in Al-Mg-Mn-Sc alloys is due to the Sc element alloying, which introduces Al ₃ (Sc, Zr) phases that significantly increase the dislocation density in the alloy. Dislocation pile-ups lead to localized stress concentration, resulting in densely distributed shear bands. Additionally, the grain size in deep cryogenic cold-worked Al-Mg-Mn-Sc alloys is smaller, with more grain boundaries, which hinder the free slip of dislocations, contributing to the increased number of shear bands. In the room temperature cold-worked samples shown in Figure 4(f), uneven deformation leads to the formation of crossed shear bands, which not only hinder further deformation but also facilitate more severe strain concentration, potentially becoming the initiation points for fracture cracks. Furthermore, due to the second-phase particles moving with the shear bands when slip is impeded, the crossed shear bands in room temperature cold-worked samples become regions where Al ₃ (Sc, Zr) phase agglomerates. During heat treatments like annealing, the short-range diffusion of Sc and Zr elements is more likely to occur, reducing the energy barrier for the coarsening of Al ₃ (Sc, Zr) phases. In contrast, uniform deformation during deep cryogenic cold-working can promote the even distribution of second-phase particles in the matrix, reducing the likelihood of local phase agglomeration or coarsening due to high stress. Uniform deformation plays a crucial role in material processing, not only by reducing localized stress concentration but also by facilitating uniform dislocation slip and accumulation. The evidence for improved uniform deformation in deep cryogenic cold-working is particularly evident in composite sheet rolling, as Song et al. ^[15] found that during the accumulative rolling of AA1050/AA5052 composite plates, interlayer necking occurred due to differences in hardness between the two aluminum alloys. Deep cryogenic cold-working after accumulative rolling significantly improved the interlayer necking and the mechanical property degradation caused by unevenly distributed shear bands. Liu et al. ^[16] discovered that room temperature rolling of Cu/Nb composite plates produced uneven high-energy interfaces, whereas deep cryogenic cold-working resulted in smooth interfaces, which enhance the alloy's thermal stability and mechanical properties.

图4（g）是基于轧制样品的EBSD结果统计和计算得到的平均晶粒尺寸和位错密度。对于Al-Mg-Mn-Sc合金而言，Al₃(Sc, Zr)相对位错的钉扎作用导致位错滑移被束缚，异号位错相消和湮灭较为困难，这种弥散第二相进一步导致位错密度显著增大，因此室温轧制和深冷轧制Al-Mg-Mn-Sc合金中的位错密度均达到较高水平，但深冷轧制具有更强的积累位错的能力。深冷轧制样品的晶格畸变更加明显，位错数量更多，而室温轧制样品中位错数量较少。在室温或更高温度下，位错会通过滑移和攀移等热激活机制消除。但是深冷轧制过程中位错的运动受到深冷环境的抑制，原子的运动和扩散也受限，热激活不足导致位错难以移动和消除，因此在变形过程中位错大量累积。这种深冷条件下的位错塞积大大增加了材料中的位错密度。高密度位错之间相互作用而产生有序的位错构型，从而使得深冷轧制样品具有更高的极限抗拉强度。
Figure 4(g) shows the average grain size and dislocation density statistically and computationally derived from EBSD results of the rolled samples. For the Al-Mg-Mn-Sc alloy, the pinning effect of Al ₃ (Sc, Zr) on relative dislocations leads to the binding of dislocation slip, making it difficult for oppositely charged dislocations to annihilate and vanish. This dispersed second phase further results in a significant increase in dislocation density. Therefore, the dislocation density in both room temperature and deep cryogenic rolling of the Al-Mg-Mn-Sc alloy reaches a high level, but deep cryogenic rolling has a stronger ability to accumulate dislocations. The lattice distortion in deep cryogenically rolled samples is more pronounced, with a higher number of dislocations, while the number of dislocations in room temperature rolled samples is lower. At room temperature or higher, dislocations are eliminated through thermal activation mechanisms such as slip and climb. However, the movement of dislocations during deep cryogenic rolling is inhibited by the deep cryogenic environment, and the diffusion and movement of atoms are also limited. Insufficient thermal activation results in the difficulty of dislocation movement and elimination, leading to a large accumulation of dislocations during deformation. This dislocation pile-up under deep cryogenic conditions significantly increases the dislocation density in the material. High-density dislocations interact with each other to form ordered dislocation configurations, thereby giving the deep cryogenically rolled samples a higher ultimate tensile strength.

深冷轧制具有显著的晶粒细化效果。深冷轧制Al-Mg-Mn-Sc合金的平均晶粒尺寸为2.8 μm，室温轧制样品的平均晶粒尺寸高出该值43%。深冷轧制工艺具有更好的晶粒细化效果得益于多个方面的作用。首先是受到高密度位错的影响，高密度位错相互缠结进一步形成位错胞和位错墙，这种高密度位错结构可以转换成亚晶等亚结构，位错积累形成的亚晶界在逐渐演变为大角度晶界后，会将原有晶粒分割成多个较小的晶粒。整个过程通过位错的排列和相互作用逐步实现晶粒的细化^{[14, 17]}，Al₃(Sc, Zr)相对位错的钉扎效应导致位错密度更高，进而促进了更显著的晶粒细化。
Deep cryogenic rolling has significant grain refinement effects. The average grain size of the Al-Mg-Mn-Sc alloy after deep cryogenic rolling is 2.8 μm, which is 43% larger than that of room temperature rolling samples. The better grain refinement effect of the deep cryogenic rolling process is due to multiple factors. Firstly, the high density of dislocations plays a crucial role, as these dislocations entangle and form dislocation cells and dislocation walls. This high density dislocation structure can transform into subgrains and other substructures. As the dislocation accumulation forms subgrain boundaries, these boundaries gradually evolve into high-angle grain boundaries, which further divide the original grains into multiple smaller grains. The entire process is achieved through the arrangement and interaction of dislocations. Additionally, the pinning effect of Al(Sc, Zr) on dislocations leads to higher dislocation density, thereby promoting more significant grain refinement.

图4（h）统计了深冷轧制和室温轧制Al-Mg-Mn-Sc合金中晶粒对应的织构类型及其体积分数（设定偏离角为20°）。Brass、Copper和S织构为轧制后Al-Mg-Mn-Sc合金中的主要织构类型。值得注意的是，在深冷轧制样品中Brass织构和Copper织构显著增强，表明深冷轧制能够有效促进这些织构的形成。对于室温轧制样品，尽管Brass和Copper织构仍然存在，但强度相对较弱。此外，室温轧制样品中还观察到了较弱的Goss织构，这种织构在深冷轧制的样品中并不显著。这些结果表明，轧制温度对织构的形成和演变具有重要影响，深冷轧制更有利于形成特定的织构类型，从而对材料的力学性能产生不同的影响。沿轧制方向拉长且平直的晶粒，其内部的织构类型较为稳定，而在局部剪切带处的拉长晶粒或细小晶粒，其织构类型相较于理想取向的偏离角发生了增大或减小，这表明局部剪切改变了晶粒取向。统计结果表明深冷轧制样品中Copper织构的含量比室温轧制样品高出约10%，达到了26.9%。深冷轧制样品中S织构的含量从57.8%减少到了49.3%，这是因为微观剪切带更加均匀且密集，局部剪切带的存在不仅细化了晶粒还削弱了S织构。Brass织构和Copper织构通常为强化织构，因为这些织构通常伴随高密度位错一起形成，能够有效提高合金的强度和硬度，室温轧制样品中交叉的剪切带显著削弱了其中的Copper织构和Brass织构。
Figure 4(h) statistically records the grain orientation types and their volume fractions corresponding to deep cryogenic and room temperature rolling of Al-Mg-Mn-Sc alloys (with a misorientation angle set at 20°). The Brass, Copper, and S textures are the main orientation types in the rolled Al-Mg-Mn-Sc alloy. Notably, in the deep cryogenic rolling samples, the Brass and Copper textures are significantly enhanced, indicating that deep cryogenic rolling effectively promotes the formation of these textures. For room temperature rolling samples, although the Brass and Copper textures still exist, their intensity is relatively weak. Additionally, room temperature rolling samples also exhibit a weak Goss texture, which is not significantly present in the deep cryogenic rolling samples. These results suggest that rolling temperature has a significant impact on texture formation and evolution, with deep cryogenic rolling more favoring the formation of specific texture types, thereby affecting the mechanical properties of the material differently. Grains elongated and straight along the rolling direction have relatively stable texture types, while elongated grains or fine grains in local shear bands have texture types with increased or decreased misorientation angles from the ideal orientation, indicating that local shear changes the grain orientation. Statistical results show that the content of the Copper texture in deep cryogenic rolling samples is about 10% higher than in room temperature rolling samples, reaching 26.9%. The content of the S texture in deep cryogenic rolling samples decreased from 57.8% to 49.3%, due to more uniform and dense micro-shear bands, where local shear bands not only refine the grains but also weaken the S texture. The Brass and Copper textures are typically strengthening textures because these textures usually form together with high-density dislocations, effectively enhancing the alloy's strength and hardness. The intersecting shear bands in room temperature rolling samples significantly weaken the Copper and Brass textures.

图4 轧制Al-Mg-Mn-Sc合金样品的IPF图、KAM图、BC图及晶粒尺寸、位错密度、织构成分统计：（a、c、e）深冷轧制样品，（b、d、f）室温轧制样品
Figure 4 IPF maps, KAM maps, BC maps, grain size, dislocation density, and crystallographic component statistics of rolled Al-Mg-Mn-Sc alloy samples: (a, c, e) deep cryogenic rolled samples, (b, d, f) room temperature rolled samples

图5（a-b）是深冷轧制和室温轧制Al-Mg-Mn-Sc合金板材的TEM微观组织。与轧制前的微观组织相比，深冷轧制和室温轧制工艺细化了晶粒尺寸且产生了大量的位错。深冷轧制样品的TEM形貌如图5（a）所示，白色箭头指示的是合金在变形过程中产生的大量位错缠结。另外，可以观察到深冷轧制样品中Al₃(Sc, Zr)相沿着轧制方向分布（如红色箭头所指），合金中还有尺寸较小的Al₆(Mn, Fe)相。相比而言，室温轧制样品中位错分布更加集中且数量更少，Al₆(Mn, Fe)相的尺寸也略大于深冷轧制样品。显著的差异在于室温轧制样品中Al₃(Sc, Zr)相分布较为集中，这与室温变形的不均匀性有关。
Figure 5(a-b) shows the TEM microstructure of deep cryogenic and room temperature rolled Al-Mg-Mn-Sc alloy sheets. Compared to the microstructure before rolling, both deep cryogenic and room temperature rolling processes refined the grain size and generated a large number of dislocations. The TEM morphology of the deep cryogenic rolled sample is shown in Figure 5(a), with white arrows indicating the numerous dislocation tangles formed during deformation of the alloy. Additionally, it can be observed that the Al ₃ (Sc, Zr) phase is distributed along the rolling direction in the deep cryogenic rolled sample (as indicated by the red arrows), while smaller Al ₆ (Mn, Fe) phase particles are also present in the alloy. In contrast, the dislocation distribution in the room temperature rolled sample is more concentrated and fewer in number, with the Al ₆ (Mn, Fe) phase particles slightly larger than in the deep cryogenic rolled sample. A significant difference is that the Al ₃ (Sc, Zr) phase is more concentrated in the room temperature rolled sample, which is related to the inhomogeneity of room temperature deformation.

图5 轧制Al-Mg-Mn-Sc合金TEM微观组织：（a）深冷轧制，（b）室温轧制
Figure 5 TEM Microstructure of 轧制 Al-Mg-Mn-Sc Alloy: (a) Deeply Cold Rolling, (b) Room Temperature Rolling

经过300℃退火1小时的深冷轧制和室温轧制Al-Mg-Mn-Sc合金样品的IPF图如图6所示。两个样品均保持拉长的纤维状晶粒组织，以晶粒拟合椭圆的短轴长作为其晶粒尺寸，其中深冷轧制后退火样品的平均晶粒尺寸为4.2 μm，室温轧制后退火样品的平均晶粒尺寸为4.5 μm。退火后，深冷轧制样品和室温轧制样品的KAM平均取向差分别为1.74×10^-2 rad和1.59×10^-2 rad。信号采集步长分别为0.2 μm和0.24 μm，计算可得，深冷轧制和室温轧制Al-Mg-Mn-Sc合金的几何必要位错密度分别为6.08×10¹⁴ m^-2和4.63×10¹⁴ m^-2。GOS图反映了样品的再结晶情况，再结晶晶粒定义为平均定向伸展小于2°的晶粒。根据图6（c, f）所示的GOS图，深冷轧制后退火样品中的再结晶晶粒比例（10.8%）低于室温轧制后退火样品中的再结晶晶粒比例（14.2%）。θ>15°被定义为大角度晶界，2°<θ<15°被定义为小角度晶界。大角度晶界在深冷轧制后退火和室温轧制后退火Al-Mg-Mn-Sc合金中的比例分别为33.4%和45.4%。
The IPF maps of the Al-Mg-Mn-Sc alloy samples after deep cold rolling and room temperature rolling, followed by 1 hour annealing at 300℃, are shown in Figure 6. Both samples retain elongated fibrous grain structures, with grain size determined by the short axis of fitted ellipses. The average grain size of the sample annealed after deep cold rolling is 4.2 μm, while that of the sample annealed after room temperature rolling is 4.5 μm. After annealing, the average KAM orientation misorientation for the deep cold rolled sample and the room temperature rolled sample are 1.74×10 ^-2 rad and 1.59×10 ^-2 rad, respectively. The signal acquisition steps are 0.2 μm and 0.24 μm, respectively, and the geometric necessary dislocation density calculated is 6.08×10 ¹⁴ m ^-2 and 4.63×10 ¹⁴ m ^-2 for the deep cold rolled and room temperature rolled Al-Mg-Mn-Sc alloy, respectively. The GOS maps reflect the recrystallization state of the samples, with recrystallized grains defined as those with an average orientation spread less than 2°. According to the GOS maps in Figure 6 (c, f), the proportion of recrystallized grains in the sample annealed after deep cold rolling (10.8%) is lower than that in the sample annealed after room temperature rolling (14.2%). Grains with θ > 15° are defined as high-angle grain boundaries, while those with 2° < θ < 15° are defined as low-angle grain boundaries. The proportion of high-angle grain boundaries in the Al-Mg-Mn-Sc alloy samples annealed after deep cold rolling and room temperature rolling are 33.4% and 45.4%, respectively.

图6 轧制Al-Mg-Mn-Sc合金300℃退火1小时IPF图、KAM图和GOS图：（a-c）深冷轧制，（d-e）室温轧制
Figure 6 IPF, KAM, and GOS maps of rolled Al-Mg-Mn-Sc alloy annealed at 300℃ for 1 hour: (a-c) deep rolling, (d-e) room temperature rolling

以上研究初步证实深冷轧制Al-Mg-Mn-Sc合金具有较好的组织热稳定性且温度对合金组织及性能的影响更加显著。根据非等温退火实验可知在450℃以上，深冷轧制Al-Mg-Mn-Sc合金的热稳定性优势更加明显。因此，进一步升高退火温度可以看到轧制温度对热稳定性更显著的影响。
The above research preliminarily 证实 s that deep cryogenic rolling of Al-Mg-Mn-Sc alloys has better organizational thermal stability, and the effect of temperature on the alloy's organization and properties is more pronounced. According to non-isothermal annealing experiments, above 450℃, the thermal stability advantage of deep cryogenically rolled Al-Mg-Mn-Sc alloys becomes more evident. Therefore, further increasing the annealing temperature can reveal a more significant impact of rolling temperature on thermal stability.

如图7所示，在480℃退火1小时后，深冷轧制和室温轧制样品之间的微观组织热稳定性差异更加显著。图7（a）所示的深冷轧制样品中，晶粒沿着轧制方向被拉长，呈现出明显的层状结构，晶粒尺寸分布更加集中，面积加权平均晶粒尺寸仅为5.3 μm，发生粗化的晶粒数量极少。图7（b）的KAM图显示，在该温度退火后合金中仍有数量较多的位错，平均KAM取向差为2.13×10^-2 rad。并且从取向差角的分布来看，合金中的应变分布相对均匀。图7（d）所示的室温轧制样品中晶粒长大的数量显著增加，但是在局部区域仍保持沿轧制方向的层状微观组织，但发生晶粒长大的区域约占到总面积的50%。从晶粒尺寸分布图来看，较大晶粒的占比明显增加，面积加权平均晶粒尺寸为6.5 μm。KAM图所展示的应变也说明室温轧制在480℃退火1小时后位错密度显著降低，粗大晶粒的内部位错基本消失，位错和应变主要集中在仍为层状结构的细晶区域，说明发生再结晶的过程是晶内无缺陷区不断长大的过程。该样品中的KAM取向差角平均值为1.21×10^-2 rad。该组样品的EBSD信号采集步长为0.5 μm，根据公式(1)可计算深冷轧制和室温轧制Al-Mg-Mn-Sc合金在480℃退火1小时后，位错密度仍分别达到2.98×10¹⁴ m^-2和1.69×10¹⁴ m^-2。
As shown in Figure 7, the thermal stability difference in microstructure between deep-rolled and room temperature rolled samples after annealing at 480°C for 1 hour is more pronounced. In Figure 7(a), the deep-rolled sample shows elongated grains along the rolling direction with a distinct lamellar structure, and the grain size distribution is more concentrated, with an area-weighted average grain size of only 5.3 μm, and a negligible number of coarsened grains. The KAM map in Figure 7(b) indicates that there are still a significant number of dislocations in the alloy after annealing at this temperature, with an average KAM misorientation of 2.13×10 ^-2 rad. Moreover, the distribution of misorientation angles suggests that the strain distribution in the alloy is relatively uniform. In Figure 7(d), the number of grains growing significantly increases in the room temperature rolled sample, but in localized regions, a lamellar microstructure along the rolling direction is still maintained. However, the area where grain growth occurs accounts for about 50% of the total area. From the grain size distribution diagram, it is evident that the proportion of larger grains has increased, with an area-weighted average grain size of 6.5 μm. The KAM map also shows that the dislocation density in the room temperature rolled sample is significantly reduced after annealing at 480°C for 1 hour, with the internal dislocations of coarse grains basically disappearing. The dislocations and strain are mainly concentrated in the fine-grained lamellar regions, indicating that the recrystallization process is the continuous growth of defect-free regions within grains. The average KAM misorientation angle for this sample is 1.21×10 ^-2 rad. The EBSD signal acquisition step size for this group of samples is 0.5 μm, and according to Equation (1), the dislocation density in the deep-rolled and room temperature rolled Al-Mg-Mn-Sc alloy after annealing at 480°C for 1 hour can be calculated to be 2.98×10 ¹⁴ m ^-2 and 1.69×10 ¹⁴ m ^-2 , respectively.

如图7所示为深冷轧制及室温轧制Al-Mg-Mn-Sc合金在480℃退火1小时后的GOS图，定义平均定向伸展小于2°的晶粒为再结晶晶粒，则深冷轧制样品和室温轧制样品中的再结晶晶粒的体积分数分别为17.3%和48.3%，说明深冷轧制样品在480℃退火1小时后也仅有少量区域的晶粒发生了再结晶，并且蓝色晶粒所代表的再结晶晶粒相对集中，样品中的红色和橙色晶粒是退火后仍存在的变形组织。室温轧制样品中也仍存在变形组织，但是数量和面积显著下降，此外，大角度晶界在深冷轧制和室温轧制样品中的占比分别为41.6%和50.8%。
As shown in Figure 7, the GOS diagram of the annealed 1 hour at 480°C Al-Mg-Mn-Sc alloy after cold rolling at deep temperature and room temperature is presented. Defining grains with an average orientation spread less than 2° as recrystallized grains, the volume fraction of recrystallized grains in the cold-rolled sample and the room-temperature-rolled sample is 17.3% and 48.3%, respectively. This indicates that only a small area of grains recrystallized in the cold-rolled sample after annealing at 480°C for 1 hour, and the recrystallized grains represented by the blue grains are relatively concentrated. The red and orange grains in the sample are the deformed structures still present after annealing. Although deformed structures also exist in the room-temperature-rolled sample, their quantity and area have significantly decreased. Additionally, the fraction of high-angle grain boundaries is 41.6% in the cold-rolled sample and 50.8% in the room-temperature-rolled sample.

图7 轧制Al-Mg-Mn-Sc合金在480℃退火1小时后的IPF图、KAM图和GOS图：（a-c）深冷轧制，（d-e）室温轧制
Figure 7 IPF, KAM, and GOS maps of annealed for 1 hour at 480℃ Al-Mg-Mn-Sc alloy after rolling: (a-c) deep drawing rolling, (d-e) room temperature rolling

退火过程中大角度晶界占比的变化也反映了Al-Mg-Mn-Sc合金的热稳定性。在轧制状态下，深冷轧制样品的大角度晶界比例为19.6%，而室温轧制样品的大角度晶界比例较高，达到25.6%。深冷轧制抑制位错湮灭而形成更高密度的位错，这导致其中小角度晶界的占比更高。随着退火的进行，小角度晶界逐渐向大角度晶界发生转变。在300℃下退火1小时后，深冷轧制样品的大角度晶界比例上升至33.4%，而室温轧制样品则上升到45.4%。退火使大角度晶界比例在两种样品中均有所增加，但室温轧制样品表现出更高的增长。在480℃下退火1小时后，深冷轧制样品的大角度晶界比例为41.6%，而室温轧制样品的比例更高，为50.8%。在相同热处理条件下，深冷轧制样品中大角度晶界的占比始终小于室温轧制样品，也反映出深冷轧制具有进一步提高热稳定性的作用。
The change in the proportion of high-angle grain boundaries during annealing also reflects the thermal stability of the Al-Mg-Mn-Sc alloy. In the rolled state, the proportion of high-angle grain boundaries in the deep-drawn samples was 19.6%, while in the room temperature rolled samples, this proportion was higher at 25.6%. Deep-drawing suppresses dislocation annihilation, leading to a higher density of dislocations, which results in a higher proportion of low-angle grain boundaries. As annealing progresses, low-angle grain boundaries gradually transform into high-angle grain boundaries. After 1 hour of annealing at 300°C, the proportion of high-angle grain boundaries in the deep-drawn samples increased to 33.4%, while in the room temperature rolled samples, it rose to 45.4%. Annealing increased the proportion of high-angle grain boundaries in both samples, but the room temperature rolled samples showed a higher increase. After 1 hour of annealing at 480°C, the proportion of high-angle grain boundaries in the deep-drawn samples was 41.6%, while in the room temperature rolled samples, it was higher at 50.8%. Under the same heat treatment conditions, the proportion of high-angle grain boundaries in the deep-drawn samples remained consistently lower than in the room temperature rolled samples, also indicating that deep-drawing has a further enhancing effect on thermal stability.

分析轧制及退火过程中位错密度的变化发现，深冷轧制样品在初始轧制态下的位错密度最高，达到7.64×10¹⁴ m^-2，而室温轧制样品的位错密度为6.55×10¹⁴ m^-2，这表明深冷轧制引入了更多的位错，与深冷环境中Al-Mg-Mn-Sc合金具有更显著的加工硬化效应有关。在300℃下退火1小时后，深冷轧制样品的位错密度降至6.08×10¹⁴ m^-2，室温轧制样品降至4.63×10¹⁴ m^-2。尽管两者的位错密度都有所下降，但深冷轧制样品仍保持更高的位错密度，这表明深冷轧制样品发生回复的程度更低。在480℃退火1小时后，深冷轧制样品的位错密度为2.98×10¹⁴ m^-2，室温轧制样品显著降低至1.69×10¹⁴ m^-2。高温退火促进了再结晶的发生，室温轧制样品的位错密度大幅降低，而深冷轧制样品的位错密度仍保持相对较高的水平。以上实验结果说明，深冷轧制样品具有更高的晶界结构和位错结构的热稳定性。
By analyzing the changes in dislocation density during the rolling and annealing processes, it was found that the dislocation density in the deep cryogenic rolled samples was the highest in the initial rolled state, reaching 7.64×10 ¹⁴ m ^-2 , while the dislocation density in the room temperature rolled samples was 6.55×10 ¹⁴ m ^{- 2} , indicating that deep cryogenic rolling introduced more dislocations, which is related to the more significant work hardening effect in the Al-Mg-Mn-Sc alloy in the deep cryogenic environment. After annealing at 300℃ for one hour, the dislocation density of the deep cryogenic rolled samples decreased to 6.08×10 ¹⁴ m ^-2 , while that of the room temperature rolled samples decreased to 4.63×10 ¹⁴ m ^-2 . Although the dislocation density of both samples decreased, the deep cryogenic rolled samples still maintained a higher dislocation density, indicating that the degree of recrystallization in the deep cryogenic rolled samples was lower. After annealing at 480℃ for one hour, the dislocation density of the deep cryogenic rolled samples was 2.98×10 ¹⁴ m ^-2 , while that of the room temperature rolled samples significantly decreased to 1.69×10 ¹⁴ m ^-2 . High-temperature annealing promoted recrystallization, and the dislocation density of the room temperature rolled samples decreased significantly, while the dislocation density of the deep cryogenic rolled samples still maintained a relatively high level. The above experimental results indicate that the deep cryogenic rolled samples have higher thermal stability of grain boundary structure and dislocation structure.

4 讨论
4 Discussion

4.1 深冷轧制抑制Al₃(Sc, Zr)相粗化的微观机制
4.1 Deep Cryogenic Cold Rolling Mechanism to Inhibit Coarsening of Al ₃ (Sc, Zr) Phase

再结晶、晶粒长大和组织软化通常是因为高温下晶界和位错的移动趋于活跃，晶粒形核后，晶界迁移随即开始发生，大角度晶界趋向于移动到缺陷密度较高的区域，而在原来的位置形成无缺陷区。因此大角度晶界的两侧存在能量差，晶界迁移速率$''v''$也随之变化^[18]：
Recrystallization, grain growth, and microstructural softening typically occur because the movement of grain boundaries and dislocations becomes more active at high temperatures. After nucleation of new grains, grain boundary migration begins immediately. High-angle grain boundaries tend to move to regions with higher defect density, leaving defect-free regions in their original positions. Therefore, there is an energy difference between the two sides of high-angle grain boundaries, and the grain boundary migration rate also changes accordingly.

  (2)

晶界迁移速率$''v''$与晶界上的压力差$''∆P''$成比例，比例系数$''M''$描述了晶界的移动性，并且依从Arrhenius关系式：
The migration rate of grain boundaries is proportional to the pressure difference on the grain boundary, with the proportionality coefficient describing the mobility of the grain boundary and following the Arrhenius relationship:

  (3)

式中，${''M''}_{\mathrm{}}$代表无温度影响时的速率常数，通常与材料的微观组织结构相关。ln(M)的斜率为，其中Q是和温度相关的晶界迁移激活能，直接影响晶界的迁移。R是气体常数。T是以开尔文为单位的绝对温度。实际上，再结晶的迁移率不可定量描述，因为晶界的储存能是难以定量的。
In the equation, ${''M''}_{\mathrm{}}$ represents the rate constant without temperature effects, typically related to the material's microstructure. The slope of ln(M) is given by, where Q is the activation energy for grain boundary migration that is temperature-dependent and directly affects grain boundary migration. R is the gas constant. T is the absolute temperature in Kelvin. Actually, the migration rate of recrystallization cannot be quantitatively described because the stored energy at grain boundaries is difficult to quantify.

Sc、Zr微合金化在Al-Mg-Mn-Sc合金中引入了纳米级的Al₃(Sc, Zr)弥散相，这些弥散相均匀分布在基体中，对位错的滑移和晶界的迁移起到了显著的钉扎作用，这种钉扎提高了晶界迁移所需要的激活能Q，进而降低了晶界的移动性。此外，Al₃(Sc, Zr)相具有优异的耐热性，其粗化温度通常超过450℃，在粗化温度以下，Al₃(Sc, Zr)相能够稳定存在，并始终具有对位错的滑移和晶界的迁移的阻碍作用，减缓了再结晶和晶粒长大的过程，使得合金在高温退火后仍可保持细晶和高密度位错组织，同时具有较好的力学性能。
Sc, Zr microalloying introduced nanoscale Al ₃ (Sc, Zr) dispersoids into the Al-Mg-Mn-Sc alloy, which are uniformly distributed in the matrix and play a significant pinning role in the slip of dislocations and migration of grain boundaries. This pinning increases the activation energy Q required for grain boundary migration, thereby reducing the mobility of grain boundaries. Additionally, the Al ₃ (Sc, Zr) phase exhibits excellent thermal stability, with its coarsening temperature typically exceeding 450°C. Below this coarsening temperature, the Al ₃ (Sc, Zr) phase remains stable and continues to impede the slip of dislocations and migration of grain boundaries, slowing down recrystallization and grain growth. This results in the alloy maintaining fine grains and a high density of dislocations even after high-temperature annealing, while also exhibiting good mechanical properties.

非等温退火至500℃时，室温轧制Al-Mg-Mn-Sc合金发生软化，这是再结晶初期的特征之一。Deng等^[19]研究发现，Al-Zn-Mg-Sc-Zr合金在475℃退火1小时才发生晶粒粗化，而完全再结晶需要600℃以上。图8展示了Sc、Zr元素在深冷轧制后退火Al-Mg-Mn-Sc合金中的存在形态，Sc、Zr元素在铝基体中形成了马蹄状的Al₃(Sc, Zr)相，其中Al₃(Sc, Zr)相分散在晶粒内或钉扎在晶界上。分散在晶粒中的Al₃(Sc, Zr)相在拉伸过程中阻碍了位错滑移，并在滑移面上形成大量位错塞积。另外，当这些位错与Al₃(Sc, Zr)相相互作用时，位错受到阻碍而形成拱形，最终绕过Al₃(Sc, Zr)相实现弥散强化。在退火后的Al-Mg-Mn-Sc合金中位错强化和弥散强化机制依然发挥重要作用^[20]，这也是深冷轧制Al-Mg-Mn-Sc合金具有更高强度的原因之一。
Annealing at 500℃ under non-isothermal conditions causes softening in room temperature rolled Al-Mg-Mn-Sc alloy, which is one of the characteristics of the early recrystallization stage. Deng et al. ^[19] found that grain growth in Al-Zn-Mg-Sc-Zr alloy occurs only after 1 hour of annealing at 475℃, while complete recrystallization requires temperatures above 600℃. Figure 8 shows the existence forms of Sc and Zr elements in the Al-Mg-Mn-Sc alloy after deep cold rolling and subsequent annealing, where Sc and Zr elements form horseshoe-shaped Al ₃ (Sc, Zr) phases in the aluminum matrix, with Al ₃ (Sc, Zr) phases dispersed within or pinned at grain boundaries. The Al ₃ (Sc, Zr) phases dispersed within the grains impede dislocation slip during tensile testing and form a large number of dislocation pile-ups on the slip planes. Additionally, when these dislocations interact with Al ₃ (Sc, Zr) phases, they are impeded and form arches, ultimately bypassing Al ₃ (Sc, Zr) phases to achieve dispersion strengthening. In the annealed Al-Mg-Mn-Sc alloy, dislocation strengthening and dispersion strengthening mechanisms still play important roles ^[20] , which is one of the reasons for the higher strength of deep cold rolled Al-Mg-Mn-Sc alloy.

图8 深冷轧制后退火Al-Mg-Mn-Sc合金中的Al₃(Sc, Zr)相：（a-c）300℃退火1小时样品，（d）480℃退火1小时退火样品
Figure 8 Al ₃ (Sc, Zr) phase in Al-Mg-Mn-Sc alloy after deep cold rolling and annealing: (a-c) Sample annealed at 300℃ for 1 hour, (d) Sample annealed at 480℃ for 1 hour

图8（b）所示为典型的Smith-Zener钉扎现象，Al₃(Sc, Zr)相恰好钉扎在晶界，这是Al₃(Sc, Zr)相可以抑制再结晶，提高组织热稳定性的有力证据。钉扎在晶界上的Al₃(Sc, Zr)相抑制了再结晶和晶粒长大。此外，Al₃(Sc, Zr)相提高了再结晶温度，从而提高了Al-Mg-Mn-Sc合金的热稳定性。此时晶界迁移的驱动力$''P''$可以表示为^{[21, 22]}：
Figure 8(b) shows the typical Smith-Zener pinning phenomenon, where Al ₃ (Sc, Zr) phase pins at the grain boundary, providing strong evidence that Al ₃ (Sc, Zr) phase can inhibit recrystallization and enhance the microstructural thermal stability. The Al ₃ (Sc, Zr) phase pinned at the grain boundary suppresses recrystallization and grain growth. Additionally, the Al ₃ (Sc, Zr) phase raises the recrystallization temperature, thereby improving the thermal stability of the Al-Mg-Mn-Sc alloy. At this point, the driving force for grain boundary migration $''P''$ can be expressed as ^{[21, 22]} .

  (4)

  (5)

  (5)

公式(4)说明晶界的迁移驱动力是晶界储存能驱动力与晶界曲率阻碍力${''P''}_{\mathrm{}}$、弥散相钉扎晶界的阻力${''P''}_{\mathrm{}}$的差值。晶界储存能驱动力可由(5)计算，其中$''k''$是位错重排因子，范围为0.1~1。是再结晶芯部的无缺陷区与高缺陷基体之间的位错密度差，随着再结晶过程的发生将会逐步减小，$''G''$表示合金的剪切模量，$''b''$是合金伯氏矢量，表达式(5)说明了缺陷密度更高的样品具有更高的再结晶驱动力。表达式(5)中是常数，$''f''$和$''d''$分别是Al₃(Sc, Zr)相的体积分数和半径，该式也反映了${''P''}_{\mathrm{}}$再结晶阻力和纳米相的体积分数成正比，半径成反比。
Equation (4) indicates that the driving force for grain boundary migration is the difference between the grain boundary storage energy driving force and the grain boundary curvature hindrance force ${''P''}_{\mathrm{}}$ , as well as the resistance to pinning grain boundaries by dispersed phases ${''P''}_{\mathrm{}}$ . The grain boundary storage energy driving force can be calculated by Equation (5), where $''k''$ is the dislocation rearrangement factor, ranging from 0.1 to 1. It represents the difference in dislocation density between the defect-free core of recrystallization and the high defect matrix, which will gradually decrease with the occurrence of the recrystallization process. $''G''$ denotes the shear modulus of the alloy, and $''b''$ is the Burgers vector of the alloy. Equation (5) shows that samples with higher defect densities have higher recrystallization driving forces. In Equation (5), $''f''$ and $''d''$ are the volume fraction and radius of the Al ₃ (Sc, Zr) phase, respectively, and this equation also indicates that the recrystallization resistance ${''P''}_{\mathrm{}}$ is proportional to the volume fraction of nanophases and inversely proportional to their radius.

此外，Al₃(Sc, Zr)相通过钉扎晶界和位错，阻碍了晶界迁移和位错运动，确保了组织的热稳定性，保持了合金优异的力学性能。图8（c）展示了Al₃(Sc, Zr)相和位错的交互作用，退火过程中位错滑移被激活，导致位错湮灭、重排，但是由于Al₃(Sc, Zr)相的阻碍，该区域内的一排位错线未能发生滑移而湮灭，保留了部分位错而实现位错强化也是深冷轧制Al-Mg-Mn-Sc合金在退火后保持较高强度的原因之一。实验结果显示，Al-Mg-Mn-Sc合金在300℃退火500小时后，依然保持了较高的抗拉强度和屈服强度。这表明Al₃(Sc, Zr)弥散相即使长期在高温环境下依旧可以发挥显著的作用，对合金的组织热稳定性具有重要贡献，有效阻碍了合金在长期高温服役时的性能退化。图8（d）所示的480℃退火样品中，Al₃(Sc, Zr)相仍然分布较为均匀。
In addition, the Al ₃ (Sc, Zr) phase impedes grain boundary migration and dislocation motion by pinning grain boundaries and dislocations, ensuring the thermal stability of the microstructure and maintaining the alloy's excellent mechanical properties. Figure 8(c) illustrates the interaction between the Al ₃ (Sc, Zr) phase and dislocations, where during annealing, dislocation slip is activated, leading to dislocation annihilation and reconfiguration. However, due to the impediment by the Al ₃ (Sc, Zr) phase, a row of dislocation lines within the region failed to slip and annihilate, retaining some dislocations to achieve dislocation strengthening, which is one of the reasons for the high strength retention of the deep cold-rolled Al-Mg-Mn-Sc alloy after annealing. Experimental results show that the Al-Mg-Mn-Sc alloy maintains high tensile strength and yield strength after 500 hours of annealing at 300°C. This indicates that the Al ₃ (Sc, Zr) dispersed phase can still play a significant role even under long-term high-temperature conditions, contributing importantly to the thermal stability of the alloy and effectively hindering the performance degradation of the alloy during long-term high-temperature service. Figure 8(d) shows that the Al ₃ (Sc, Zr) phase is still distributed relatively uniformly in the sample annealed at 480°C.

Al₃(Sc, Zr)相在室温轧制和深冷轧制样品中的分布特征不同，进一步分析发现，Al₃(Sc, Zr)相的尺寸也有差别。如图9所示，通过Sc元素的分布确定Al₃(Sc, Zr)相位置及其尺寸。使用Image Pro plus软件统计多张图片中Al₃(Sc, Zr)相的尺寸及面积，并设定Al₃(Sc, Zr)相的最小直径为10 nm以避免将固溶在基体中的Sc原子也纳入统计样本。统计结果显示，Al₃(Sc, Zr)相在深冷轧制和室温轧制样品中的平均尺寸分别为21 nm和29 nm。假设Al₃(Sc, Zr)相面积分数近似等同于体积分数，深冷轧制和室温轧制Al-Mg-Mn-Sc合金中Al₃(Sc, Zr)相的体积分数分别为0.38%和0.39%。在480℃退火1小时后，深冷轧制和室温轧制样品中微观组织差异显著增大，观察Al₃(Sc, Zr)相的形貌发现，其中的第二相形态发生了显著变化，其中深冷轧制样品中Al₃(Sc, Zr)相呈马蹄状弥散分布在铝基体内，统计得到Al₃(Sc, Zr)相的平均直径保持为21 nm。但是室温轧制样品中Al₃(Sc, Zr)相发生显著粗化，根据Sc元素的EDS分布图统计得到样品中Al₃(Sc, Zr)相的平均尺寸为36 nm，达到深冷轧制样品中Al₃(Sc, Zr)相直径的1.7倍。
The distribution characteristics of Al ₃ (Sc, Zr) phases in samples subjected to room temperature rolling and deep cold rolling are different. Further analysis revealed that the sizes of Al ₃ (Sc, Zr) phases also differ. As shown in Figure 9, the positions and sizes of Al ₃ (Sc, Zr) phases were determined using the distribution of Sc elements. Using Image Pro Plus software, the sizes and areas of multiple images of Al ₃ (Sc, Zr) phases were statistically analyzed, with a minimum diameter of 10 nm set for Al ₃ (Sc, Zr) phases to avoid including Sc atoms dissolved in the matrix in the statistical sample. The statistical results show that the average sizes of Al ₃ (Sc, Zr) phases in deep cold rolled and room temperature rolled samples are 21 nm and 29 nm, respectively. Assuming that the area fraction of Al ₃ (Sc, Zr) phases is approximately equivalent to the volume fraction, the volume fractions of Al ₃ (Sc, Zr) phases in Al-Mg-Mn-Sc alloys after deep cold rolling and room temperature rolling are 0.38% and 0.39%, respectively. After annealing at 480°C for 1 hour, the microstructural differences between deep cold rolled and room temperature rolled samples significantly increase. Observations of the morphology of Al ₃ (Sc, Zr) phases reveal significant changes in the second phase morphology. In the deep cold rolled samples, Al ₃ (Sc, Zr) phases are diffusely distributed in the aluminum matrix in a horseshoe shape, and the average diameter of Al ₃ (Sc, Zr) phases remains at 21 nm. However, in the room temperature rolled samples, Al ₃ (Sc, Zr) phases significantly coarsen, and the average size of Al ₃ (Sc, Zr) phases, as statistically determined from the EDS distribution map, is 36 nm, which is 1.7 times the diameter of Al ₃ (Sc, Zr) phases in the deep cold rolled samples.

图9 轧制Al-Mg-Mn-Sc合金中Al₃(Sc, Zr)相形貌，Sc元素分布及平均尺寸统计：（a-c）深冷轧制样品，（d-f）室温轧制样品，（g-i）室温轧制后480℃退火1小时样品
Figure 9 Morphology of Al ₃ (Sc, Zr) phase, Sc element distribution, and statistical average size in rolled Al-Mg-Mn-Sc alloy: (a-c) cryogenic rolled samples, (d-f) room temperature rolled samples, (g-i) room temperature rolled samples annealed at 480°C for 1 hour

在480℃退火1小时后，室温轧制后退火样品中Al₃(Sc, Zr)相已有发生粗化的迹象，演变为尺寸更大的球状Al₃(Sc, Zr)相，并且失去与基体的共格关系，减弱了钉扎效应。Al₃(Sc, Zr)相的球化涉及退火过程中Sc和Zr元素的短程迁移。由于室温轧制后退火样品中Al₃(Sc, Zr)相发生粗化，表达式(5)说明半径d增大，弥散相阻碍晶界滑移的阻力减小，因此粗化的Al₃(Sc, Zr)相对晶界的钉扎作用显著下降，进而对再结晶的阻碍作用减小。这也印证了非等温退火500℃时仅有室温轧制的Al-Mg-Mn-Sc合金发生晶粒粗化的现象。深冷轧制样品具有更高热稳定性的原因在于其中弥散相的分布更加均匀，Al₃(Sc, Zr)相的均匀分布增强了晶界的钉扎效应，从而使得深冷轧制过程获得的细晶组织得以保留，这与应变、剪切带、位错等微观组织的均匀分布是具有一致性的。Al₃(Sc, Zr)相提高了，降低了在高温下晶界的迁移速度v和驱动力P，有效防止了晶粒长大对合金性能的负面影响。
After annealing at 480℃ for 1 hour, there are signs of coarsening of the Al ₃ (Sc, Zr) phase in the samples after room temperature rolling, transforming into larger spherical Al ₃ (Sc, Zr) phase, and losing its coherent relationship with the matrix, thereby weakening the pinning effect. The spheroidization of Al ₃ (Sc, Zr) phase involves short-range migration of Sc and Zr elements during annealing. Due to the coarsening of the Al ₃ (Sc, Zr) phase in the samples after room temperature rolling, expression (5) indicates that the radius d increases, reducing the hindrance to grain boundary sliding by the dispersed phase, and thus the pinning effect of the coarsened Al ₃ (Sc, Zr) phase on grain boundaries decreases, leading to a reduced hindrance to recrystallization. This also confirms that only the Al-Mg-Mn-Sc alloy subjected to room temperature rolling undergoes grain coarsening during non-isothermal annealing at 500℃. The reason for the higher thermal stability of the deep cold-rolled samples is the more uniform distribution of the dispersed phase, with the uniform distribution of Al ₃ (Sc, Zr) phase enhancing the pinning effect on grain boundaries, thus allowing the fine-grained structure obtained during deep cold rolling to be retained, which is consistent with the uniform distribution of strain, shear bands, and dislocations. The increase in Al ₃ (Sc, Zr) phase reduces the grain boundary migration velocity v and driving force P at high temperatures, effectively preventing the negative impact of grain growth on the properties of the alloy.

图10展示了深冷轧制提高Al-Mg-Mn-Sc合金组织热稳定性的微观机制，该图中所表达的信息均与实验所观察到的结果相对应。与室温轧制相比，深冷轧制细化晶粒和Al₆(Mn, Fe)第二相的效果更加明显，并且进一步提高了合金中的位错密度和小角度晶界的比例，还产生了亚晶结构。这些结构在退火过程中能够稳定地存在，阻止了大角度晶界的快速迁移，抑制了晶粒的长大，小角度晶界的存在增强了材料的抗热变形能力，从而提升了材料的热稳定性。差异更为明显的是深冷轧制样品中形成平行剪切带，但是室温轧制样品中由于不均匀变形而形成交叉剪切带，Al₃(Sc, Zr)弥散相随剪切带运动而在剪切带交叉的区域发生聚集。在退火过程中，聚集的Al₃(Sc, Zr)弥散相由于Sc、Zr元素短程扩散而长大成粗大的Al₃(Sc, Zr)相，失去对晶界和位错的钉扎作用，因此室温轧制样品中Al₃(Sc, Zr)相尺寸更大，更多的区域发生了再结晶。图10明晰了深冷轧制促进Al₃(Sc, Zr)相均匀分布并抑制其粗化的微观机理，厘清了深冷轧制Al-Mg-Mn-Sc合金具有更高热稳定性的内在机制。
Figure 10 illustrates the micro-mechanisms by which deep cryogenic rolling enhances the thermal stability of the microstructure in Al-Mg-Mn-Sc alloys, with the information presented in the figure corresponding to the experimental observations. Compared to room temperature rolling, deep cryogenic rolling more effectively refines the grain size and the Al ₆ (Mn, Fe) secondary phase, further increasing the dislocation density and the proportion of small-angle grain boundaries, and inducing subgrain structures. These structures can stably exist during annealing, preventing the rapid migration of high-angle grain boundaries, inhibiting grain growth, and enhancing the material's resistance to thermal deformation through the presence of small-angle grain boundaries, thus improving the thermal stability. Notably, deep cryogenic rolling samples form parallel shear bands, whereas room temperature rolling samples form cross shear bands due to uneven deformation. The Al ₃ (Sc, Zr) dispersions move with the shear bands and aggregate at the intersections. During annealing, the aggregated Al ₃ (Sc, Zr) dispersions grow into coarse Al ₃ (Sc, Zr) phases due to the short-range diffusion of Sc and Zr elements, losing their pinning effect on grain boundaries and dislocations. Consequently, the Al ₃ (Sc, Zr) phases in room temperature rolling samples are larger, with more areas undergoing recrystallization. Figure 10 elucidates the micro-mechanisms by which deep cryogenic rolling promotes the uniform distribution and inhibits the coarsening of Al ₃ (Sc, Zr) phases, clarifying the intrinsic mechanisms for the higher thermal stability of deep cryogenic rolling Al-Mg-Mn-Sc alloys.

图10 深冷轧制提高Al-Mg-Mn-Sc合金热稳定性的微观机制
Figure 10 Microscopic Mechanism for Enhancing Thermal Stability of Al-Mg-Mn-Sc Alloys through Deep Cold Rolling

4.2 Al-Mg-Mn-Sc合金力学性能热稳定性及其强塑性协调
4.2 Thermal Stability of Mechanical Properties and Coordination of Strength and Plasticity in Al-Mg-Mn-Sc Alloys

室温轧制和深冷轧制Al-Mg-Mn-Sc合金的硬度差距较小，但在非等温退火过程中，各个样品的硬度变化趋势显著不同，硬度的变化是其力学性能和热稳定性的直观反映。如图2（a）所示，深冷轧制Al-Mg-Mn-Sc合金的硬度从141.4 HV下降至97.8 HV，下降幅度为30.8%，室温轧制样品的硬度从129.9 HV下降至85.0 HV，下降幅度为35.6%。非等温退火后，深冷轧制样品仍保持更高的硬度，并且退火过程中硬度下降幅度更小，充分说明深冷轧制Al-Mg-Mn-Sc合金的力学性能具有更高的热稳定性。
The hardness difference between room temperature rolling and deep cryogenic rolling of Al-Mg-Mn-Sc alloys is small, but during non-isothermal annealing, the hardness change trends of the various samples are significantly different. The change in hardness is an intuitive reflection of their mechanical properties and thermal stability. As shown in Figure 2(a), the hardness of the deep cryogenically rolled Al-Mg-Mn-Sc alloy decreases from 141.4 HV to 97.8 HV, a decrease of 30.8%, while the hardness of the room temperature rolled sample decreases from 129.9 HV to 85.0 HV, a decrease of 35.6%. After non-isothermal annealing, the deep cryogenically rolled samples still maintain higher hardness, and the decrease in hardness during the annealing process is smaller, fully demonstrating that the mechanical properties of deep cryogenically rolled Al-Mg-Mn-Sc alloys have higher thermal stability.

在深冷轧制Al-Mg-Mn-Sc合金的强化机制研究中发现，位错强化对Al-Mg-Mn-Sc合金屈服强度的贡献超过30%，退火过程中，由于位错很容易受到温度的影响而发生重排和湮灭，因此屈服强度下降较为显著^[23]。例如300℃退火3分钟后，屈服强度的降幅超过10%，但与室温轧制样品相比，深冷轧制样品在不同制度退火后均始终保持更高的屈服强度，这可以归因于深冷轧制样品中具有更高的位错密度，即使部分位错湮灭，也仍可以保持更高的位错密度和位错强化贡献。另一方面，Al₃(Sc, Zr)弥散相对位错的钉扎作用提高了Al-Mg-Mn-Sc合金中发生位错湮灭的能量势垒，使得退火后仍保留更多的位错^{[22, 24]}，从而减少了屈服强度的损失。这在深冷轧制样品中表现得尤为明显。
In the study of strengthening mechanisms in deep cold rolled Al-Mg-Mn-Sc alloys, it was found that dislocation strengthening contributes more than 30% to the yield strength of the Al-Mg-Mn-Sc alloy. During annealing, dislocations are easily affected by temperature and undergo rearrangement and annihilation, leading to a significant decrease in yield strength ^[23] . For example, after annealing at 300°C for 3 minutes, the yield strength decreases by more than 10%. However, deep cold rolled samples maintain higher yield strength after different annealing regimes compared to samples rolled at room temperature, which can be attributed to the higher dislocation density in deep cold rolled samples, even though some dislocations are annihilated, they still maintain a higher dislocation density and dislocation strengthening contribution. On the other hand, the Al ₃ (Sc, Zr) precipitates have a pinning effect on dislocations, which increases the energy barrier for dislocation annihilation in the Al-Mg-Mn-Sc alloy, allowing more dislocations to be retained after annealing ^{[22, 24]} , thus reducing the loss in yield strength. This is particularly evident in deep cold rolled samples.

深冷轧制Al-Mg-Mn-Sc合金具有很高的微观组织热稳定性，深冷轧制得到的纤维状细晶组织在退火过程中得以保留，因此退火后细晶强化机制仍对屈服强度具有较高贡献。另一方面，由于Al₃(Sc, Zr)弥散相对位错的钉扎效应，Al-Mg-Mn-Sc合金在300℃退火后仍有较高密度的位错，继续升高温度，位错将进一步减少。此外，室温轧制样品中不仅位错密度下降，还发生了弥散相粗化。粗化的Al₃(Sc, Zr)相对位错和晶界的钉扎作用下降，进一步导致位错密度减小。根据公式（4）和（5）可知，弥散相半径增大，弥散强化作用减小。因此，位错密度的下降和Al₃(Sc, Zr)相的粗化会导致位错强化和弥散相强化的贡献都会降低^[8]，这也是室温轧制Al-Mg-Mn-Sc合金的屈服强度始终低于深冷轧制样品的原因之一。即使在450℃退火1小时，深冷轧制Al-Mg-Mn-Sc合金的屈服强度仍达到259 MPa，比室温轧制样品高30 MPa。因此深冷轧制对合金屈服强度的热稳定性具有重要贡献。
Deep cryogenic rolling of Al-Mg-Mn-Sc alloys exhibits high microstructural thermal stability. The fibrous fine-grained microstructure obtained through deep cryogenic rolling is retained during annealing, thus maintaining a significant contribution of grain refinement strengthening mechanisms to the yield strength. On the other hand, due to the pinning effect of Al ₃ (Sc, Zr) precipitates on dislocations, the Al-Mg-Mn-Sc alloy still has a high density of dislocations even after annealing at 300°C. Further increasing the temperature leads to a reduction in dislocation density. Additionally, at room temperature, not only does the dislocation density decrease, but also the coarsening of the precipitates occurs. The coarsening of Al ₃ (Sc, Zr) precipitates reduces their pinning effect on dislocations and grain boundaries, further leading to a decrease in dislocation density. According to formulas (4) and (5), an increase in the radius of precipitates results in a decrease in precipitation strengthening. Therefore, the decrease in dislocation density and the coarsening of Al ₃ (Sc, Zr) precipitates will reduce the contributions of dislocation strengthening and precipitation strengthening, respectively. This is one of the reasons why the yield strength of room temperature rolled Al-Mg-Mn-Sc alloys is lower than that of deep cryogenically rolled samples. Even after annealing at 450°C for one hour, the yield strength of deep cryogenically rolled Al-Mg-Mn-Sc alloys reaches 259 MPa, which is 30 MPa higher than that of room temperature rolled samples. Therefore, deep cryogenic rolling plays an important role in enhancing the thermal stability of the alloy's yield strength.

在车身设计的选材过程中，通常既需要考虑材料的屈服强度，也关注材料的极限抗拉强度。例如，车身中的承力梁、柱等结构部件，通常要求材料在服役过程中不能发生塑性变形，因此屈服强度是主要考虑因素。除此之外，车身中的其他覆盖件需要一些塑性变形能力来吸收和耗散碰撞能量，将撞击能量逐渐消耗，从而减缓冲击力的传递，进而降低车身内部的加速度峰值，减少车内乘员受到的瞬时冲击力，保护乘员不受直接伤害。从安全设计的角度，这些部位选材时主要考虑在极端负载下所能承受的最大应力，因此更需要关注材料的抗拉强度。5xxx铝合金主要用于前舱盖、后备厢盖、车身侧板、顶板等覆盖件以及地板系统和储能系统外壳，因此对车身用5xxx铝合金而言，更侧重于关注材料的抗拉强度。
In the material selection process for vehicle body design, both the yield strength and the ultimate tensile strength of materials are typically considered. For example, load-bearing beams and columns in the body structure usually require that the material does not undergo plastic deformation during service, making the yield strength the primary consideration. Additionally, other body panels require some degree of plastic deformation to absorb and dissipate collision energy, gradually consuming the impact energy to mitigate the transmission of impact forces, thereby reducing the peak acceleration inside the vehicle and minimizing the instantaneous impact force on occupants, thus protecting them from direct injury. From a safety design perspective, these areas are primarily selected based on the maximum stress they can withstand under extreme loads, so the tensile strength is more critical. 5xxx aluminum alloys are mainly used for hood, trunk lid, side panels, roof panels, floor systems, and storage system housings. Therefore, for 5xxx aluminum alloys used in the vehicle body, more emphasis is placed on the tensile strength of the material.

本研究中Al-Mg-Mn-Sc合金属于中镁铝合金，众所周知，5xxx铝合金的强度随着Mg含量的增加而提高。图11展示了类似研究中所报道的成分相似的5xxx铝合金的力学性能。AA5083-H111板材的极限抗拉强度为331 MPa，屈服强度为239 MPa，断裂延伸率为16.4%^[25]。Krishna等^[12]研究了深冷轧制和室温轧制50%压下率的AA5083板材的力学性能，室温轧制和深冷轧制板材的抗拉强度分别为409 MPa和423 MPa，而它们的断裂延伸率分别为6%和7%。当在合金中添加Zn和Ag元素时，时效热处理可以增强合金的强度^[26]，热机械处理（TMT）使Al-4Mg-2Zn-0.3Ag合金的抗拉强度和断裂延伸率分别提高到425 MPa和14%。在Al-4.2Mg合金中添加Sc元素后，Al-Mg合金的力学性能显著提高^[27]。Fang等^[28]研究了轧制和退火工艺对Al-Mg-Mn-Sc-Zr合金力学性能的影响，在300℃下退火1小时达到最佳的力学性能，此时合金的抗拉强度和屈服强度分别达到398 MPa和278 MPa，而断裂延伸率小于10%。Ren等^[29]利用选区激光熔覆（SLM）技术制备了Al-Mg-Mn-Sc-Zr合金，其抗拉强度为320 MPa，断裂延伸率约18%。Ma等^[30]同样使用SLM工艺制备了含有0.7 wt.% Sc的Al-Mg-Mn-Sc-Zr合金，获得了抗拉强度362 MPa，断裂延伸率11.2%的拉伸力学性能，合金还经过了300℃和325℃的热处理，处理后合金的抗拉强度分别显著提高到479 MPa和511 MPa，而断裂延伸率下降至6.6%和7.3%。Yin等^[31]报告称，热轧（HR）处理的Al-5Mg-0.2Sc-0.1Zr板材的抗拉强度为398 MPa，断裂延伸率为18%。Zhu等^[32]利用室温轧制的Al-Mg-Mn-Sc-Zr板材作为搅拌摩擦焊（FSW）的原材料，板材的抗拉强度为419 MPa，断裂延伸率为12.2%。Li等^[33]利用激光粉末床熔化（LPBF）技术制备了Al-Mg-Mn-Sc-Zr合金，并报告称在300℃下时效热处理4小时后，合金的抗拉强度达到502 MPa，断裂延伸率约为7%。
This study focuses on an Al-Mg-Mn-Sc alloy with medium magnesium content, and it is well-known that the strength of 5xxx aluminum alloys increases with higher Mg content. Figure 11 shows the mechanical properties of a 5xxx aluminum alloy with similar composition as reported in other studies. The ultimate tensile strength of AA5083-H111 sheet is 331 MPa, with a yield strength of 239 MPa and a fracture elongation of 16.4%. Krishna et al. ^[12] investigated the mechanical properties of AA5083 sheets subjected to deep cold rolling and room temperature rolling at 50% reduction, with tensile strengths of 409 MPa and 423 MPa, and fracture elongations of 6% and 7%, respectively. When Zn and Ag elements are added to the alloy, aging heat treatment can enhance the strength of the alloy ^[26] , while thermomechanical processing (TMT) increases the tensile strength and fracture elongation of the Al-4Mg-2Zn-0.3Ag alloy to 425 MPa and 14%, respectively. The addition of Sc to the Al-4.2Mg alloy significantly improves the mechanical properties of Al-Mg alloys ^[27] . Fang et al. ^[28] studied the effects of rolling and annealing processes on the mechanical properties of Al-Mg-Mn-Sc-Zr alloys, achieving optimal mechanical properties after 1 hour of annealing at 300°C, with a tensile strength of 398 MPa and a yield strength of 278 MPa, and a fracture elongation of less than 10%. Ren et al. ^[29] prepared Al-Mg-Mn-Sc-Zr alloys using selective laser melting (SLM) technology, with a tensile strength of 320 MPa and a fracture elongation of about 18%. Ma et al. ^[30] used the SLM process to prepare Al-Mg-Mn-Sc-Zr alloys containing 0.7 wt.% Sc, achieving tensile strengths of 362 MPa and 479 MPa and 511 MPa, and fracture elongations of 11.2%, 6.6%, and 7.3% after heat treatments at 300°C and 325°C, respectively. Yin et al. ^[31] reported that the tensile strength of HR-treated Al-5Mg-0.2Sc-0.1Zr sheets was 398 MPa, with a fracture elongation of 18%. Zhu et al. ^[32] used Al-Mg-Mn-Sc-Zr sheets processed at room temperature as raw materials for friction stir welding (FSW), with a tensile strength of 419 MPa and a fracture elongation of 12.2%. Li et al. ^[33] prepared Al-Mg-Mn-Sc-Zr alloys using laser powder bed fusion (LPBF) technology, and reported a tensile strength of 502 MPa and a fracture elongation of about 7% after 4 hours of aging heat treatment at 300°C.

图11 本研究工作与类似5xxx合金的性能对比^{[8, 12, 25-30, 32-36]}
Figure 11 Comparison of the Performance of This Study Work with Similar 5xxx Alloys ^{[8, 12, 25-30, 32-36]}

增加Mg含量至6 wt.%，5xxx铝合金力学性能可以小幅度增加。Tang等^[34] 研究了利用变极性等离子弧焊接技术（VPPA）制备的Al-Mg-Mn-Sc合金的力学性能，焊接母材的极限抗拉强度为429 MPa，屈服强度为288 MPa，断裂延伸率为13.5%。焊接点的抗拉强度和断裂延伸率分别为327 MPa和9.2%。在另一项研究中，室温轧制Al-Mg-Mn-Sc合金经过300℃退火1小时后抗拉强度为422 MPa，断裂延伸率为15.4%^[8]。Tong等^[35]对Al-Mg-Mn-Sc-Zr合金进行320℃退火1小时处理，合金的抗拉强度和断裂延伸率分别为370 MPa和18%。经过200℃退火1小时处理后，室温轧制后退火的Al-Mg-Mn-Zr-Sc合金的抗拉强度为463 MPa，断裂延伸率为11.4%。此外，Er元素合金化的5xxx铝合金的抗拉强度和断裂延伸率分别为444 MPa和11.2%^[36]。如图11所示，本研究中深冷轧制后退火的Al-Mg-Mn-Sc-Zr合金的抗拉强度达到428 MPa，断裂延伸率为18.4%。断裂延伸率的增加是由于退火降低了位错密度并为加工硬化提供了足够的空间^[37]。本研究中深冷轧制后退火Al-Mg-Mn-Sc合金的极限抗拉强度和断裂延伸率的乘积超过了7500 MPa∙%，为高性能Al-Mg-Mn-Sc合金的工业化生产提供了实用的参考。
Increasing the Mg content to 6 wt.% slightly enhances the mechanical properties of 5xxx aluminum alloys. Tang et al. ^[34] studied the mechanical properties of Al-Mg-Mn-Sc alloys fabricated using variable polarity plasma arc welding (VPPA) technology, with the base material's ultimate tensile strength reaching 429 MPa, yield strength 288 MPa, and fracture elongation 13.5%. The tensile strength and fracture elongation at the weld point were 327 MPa and 9.2%, respectively. In another study, room temperature rolled Al-Mg-Mn-Sc alloys exhibited a tensile strength of 422 MPa and a fracture elongation of 15.4% after 1 hour of annealing at 300°C ^[8] . Tong et al. ^[35] annealed Al-Mg-Mn-Sc-Zr alloys at 320°C for 1 hour, resulting in a tensile strength of 370 MPa and a fracture elongation of 18%. After 1 hour of annealing at 200°C, the tensile strength of room temperature rolled and annealed Al-Mg-Mn-Zr-Sc alloys was 463 MPa, and the fracture elongation was 11.4%. Additionally, the tensile strength and fracture elongation of 5xxx aluminum alloys alloyed with Er elements were 444 MPa and 11.2%, respectively ^[36] . As shown in Figure 11, the tensile strength of the Al-Mg-Mn-Sc-Zr alloy after deep cold rolling and annealing in this study reached 428 MPa, with a fracture elongation of 18.4%. The increase in fracture elongation is attributed to annealing, which reduces dislocation density and provides sufficient space for work hardening ^[37] . The product of the ultimate tensile strength and fracture elongation of the deep cold rolled and annealed Al-Mg-Mn-Sc alloy in this study exceeded 7500 MPa·%, providing a practical reference for the industrial production of high-performance Al-Mg-Mn-Sc alloys.

5 结论
5 Conclusion

（1）深冷轧制具有更强的积累位错的能力。Al₃(Sc, Zr)相对位错的钉扎作用导致位错运动被束缚，深冷环境抑制位错湮灭，二者协同作用导致异号位错相消和湮灭较为困难，促进高密度位错在深冷轧制Al-Mg-Mn-Sc合金中大量积累。
(1) Deep cryogenic rolling has a stronger ability to accumulate dislocations. The pinning effect of Al ₃ (Sc, Zr) on relative dislocations restrains dislocation motion, and the deep cryogenic environment suppresses dislocation annihilation. The synergistic effect of these factors makes it difficult for opposite-sign dislocations to annihilate and be eliminated, promoting the accumulation of high-density dislocations in deep cryogenic rolled Al-Mg-Mn-Sc alloys.

（2）深冷轧制均匀变形可促使Al₃(Sc, Zr)相均匀分布，进而抑制了退火过程中Sc、Zr元素短程扩散及其导致的Al₃(Sc, Zr)相粗化。Al₃(Sc, Zr)相阻碍高温下的晶界迁移和位错攀移，保留深冷轧制样品中的细晶组织和高密度位错，这是退火过程中深冷轧制Al-Mg-Mn-Sc合金保持微观组织热稳定性和更高力学性能的关键。
(2) Deep cold rolling-induced uniform deformation promotes the uniform distribution of Al ₃ (Sc, Zr) phases, thereby suppressing short-range diffusion of Sc and Zr elements during annealing and the subsequent coarse-graining of Al ₃ (Sc, Zr) phases. Al ₃ (Sc, Zr) phases hinder grain boundary migration and dislocation climb at high temperatures, preserving fine grain structure and high dislocation density in deep cold rolled samples. This is crucial for maintaining microstructural thermal stability and higher mechanical properties in the annealed Al-Mg-Mn-Sc alloy.

（3）深冷轧制Al-Mg-Mn-Sc合金在300℃退火1小时后抗拉强度为428 MPa，与退火前样品相比，下降幅度小于7%，而断裂延伸率提高了2倍以上（18.4%），断裂延伸率和抗拉强度的乘积超过了7500 MPa∙%，高于类似研究中Al-Mg-Mn-Sc合金的力学性能。退火过程中，深冷轧制样品始终保持比室温轧制样品更高的强度。
(3) The tensile strength of the deep-cold rolled Al-Mg-Mn-Sc alloy annealed at 300°C for 1 hour is 428 MPa, decreasing by less than 7% compared to the annealed sample before annealing, while the fracture elongation increases more than two times (18.4%). The product of the fracture elongation and tensile strength exceeds 7500 MPa%, which is higher than the mechanical properties of similar studies on Al-Mg-Mn-Sc alloys. During annealing, the deep-cold rolled samples maintain a higher strength than the room temperature rolled samples.

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