目的 针对宽幅AZ31镁合金轧板在多道次热轧过程中因道次间重复补温引发的晶粒细化-粗化交替现象及混晶组织形成问题,揭示混晶组织在退火过程中的动态演变规律,阐明其对微观组织与力学性能的调控机制,为实现终轧板材组织性能的精准调控提供理论基础。方法 基于含多尺度晶粒、剪切带及孪晶的混晶组织试样,系统研究其在不同退火温度（170~300 ℃）和保温时间（0.5~3 h）下的演变行为,以及对轧板力学性能的影响规律。结果 当退火温度超过200 ℃时,混晶组织得到显著改善,材料组织均匀性提高。晶粒尺寸随退火时间的延长呈现先减小后增大的特征性演变趋势,且退火温度升高会强化这一趋势。在170~300 ℃温度范围内,退火温度主导拉伸强度,而保温时间主要影响塑性。最大伸长率出现在250 ℃-2 h条件下,达24.5%,这归因于充分的再结晶形核和孪晶显著减少的共同作用。在相同退火温度下,硬度多在1 h保温处理后达到峰值,这种非线性演变源于晶粒等轴化转变与孪晶演化行为的竞争机制。结论 通过合理选择退火温度和时间,可改善组织均匀性并平衡强度与塑性,为宽幅AZ31镁合金轧板的退火工艺优化提供重要参考。
Abstract
The work aims to elucidate the dynamic evolution mechanisms of mixed-grain structures in AZ31 magnesium alloy sheets during annealing, to address the issue of alternating grain refinement and coarsening along with mixed-grain formation caused by repeated inter-pass reheating in conventional multi-pass hot rolling, clarify the influence of annealing on microstructure and mechanical properties, and provide a theoretical foundation for precise control of the final rolled sheet's performance. Based on mixed-grain samples containing multi-scale grains, shear bands, and twins, their microstructural evolution under varying annealing temperature (170-300 ℃) and holding periods (0.5-3 h) were systematically investigated. The corresponding effects on mechanical properties were analyzed. When the annealing temperature exceeded 200 ℃, the mixed-grain structure was significantly improved, enhancing microstructural homogeneity. The grain size demonstrated a characteristic evolution pattern of initial refinement followed by coarsening with prolonged annealing time, a trend that became more pronounced at elevated temperature. Within the 170-300 ℃ range, annealing temperature dominated tensile strength, while the holding period primarily affected ductility. The maximum elongation (24.5%) occurred at 250 ℃-2 h, attributed to sufficient recrystallization nucleation and pronounced twin reduction. At fixed temperature, hardness typically peaked after 1 h. This nonlinear behavior stemmed from competing mechanisms between grain equiaxed transformation and twin evolution. Rational selection of annealing temperature and time can enhance microstructural uniformity and balance strength-ductility trade-offs, offering critical guidance for optimizing annealing processes in wide AZ31 magnesium alloy sheets.
关键词
镁合金 /
轧制 /
混晶组织 /
退火工艺 /
再结晶 /
力学性能
Key words
magnesium alloy /
rolling /
mixed-grain structure /
annealing process /
recrystallization /
mechanical properties
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基金
山西省高等学校科技创新项目（2022L608）; 忻州市重点研发计划项目（20240106）; 国家自然科学基金（52105388, 52504420）
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