Tailoring bimodal grain structure to achieve simultaneous improvement of strength and ductility in magnesium alloys at cryogenic temperatures

作者：Jing Zuo, T. Nakata, Chao Xu, Mingquan Zhang, Enyu Guo, Kun-kun Deng, Kai-bo Nie, Xiaojun Wang, S. Kamado, Lin Geng · 发表于：Journal of Magnesium and Alloys · 年份：2025 · DOI：10.1016/j.jma.2025.09.015 · 被引用次数：7 · 研究领域：Magnesium Alloys: Properties and Applications、Aluminum Alloys Composites Properties、Aluminum Alloy Microstructure Properties

Magnesium (Mg) alloys typically suffer from cold brittleness at cryogenic temperatures (CT), where strength significantly increases and ductility decreases with decreasing temperature. This study investigates the improvement of the strength-ductility balance at CT in Mg-3.6Y (wt.%) alloys with a bimodal grain structure, consisting of fine dynamically recrystallized (DRXed) grains and elongated unDRXed grains. The results demonstrate that the sample with ∼50 % DRXed region fraction achieves a remarkable strength-ductility synergy at CT. Dislocation strengthening in the unDRXed regions and grain boundary strengthening in the DRXed regions increase the tensile yield strength (TYS) by 1.6 times at CT compared to room temperature (RT). Concurrently, activation of {10 1 ¯ 2} tensile twinning and non-basal slip systems in DRXed regions, including prismatic 〈 a 〉 and pyramidal I 〈 c + a 〉 slips, along with abnormal pyramidal slip within unDRXed grains, reduces fracture elongation by only 1 % relative to RT. Furthermore, the bimodal grain structure effectively alleviates strain localization through strain partitioning between DRXed and unDRXed grains, leading to the formation of interface-affected zones (IAZs) that promote the accumulation of geometrically necessary dislocations (GNDs) and enhance hetero-deformation-induced (HDI) hardening. At CT, the IAZs become wider and more pronounced, indicating enhanced GND accumulation that promotes stronger strain partitioning and more effecti...