室温下对AZ31镁合金进行多向多道次变形, 制备亚微米和纳米级细晶镁合金. 通过OM, SEM/EBSD及TEM观察研究不同累积应变量的显微组织及取向演化. 发现低应变多向多道次压缩变形可避免镁合金室温变形下的迅速失稳断裂, 能够累积很大的真应变; 变形初期晶粒中产生大量{1012} c轴拉伸孪晶, 随后$c$轴压缩孪晶的密度逐渐增加且均匀分布于晶粒内, 孪晶分割细化原始晶粒的同时, 压缩孪晶诱发的动态再结晶开始沿孪晶密集与交叉处产生, 将组织进一步细化; 细晶区随着变形道次的增加逐渐增多, 15个道次后整个组织被均匀细化至80-150 nm; 且单道次变形量Δε在0.05-0.1之间取值越大, 晶粒细化效果越显著, 细晶分布越均匀.
Twining--induced grain refinement in magnesium alloy AZ31 has been studied by using multiple compression, i.e., changing the loading direction after each pass. The tests were carried out to 50 passes at room temperature with pass strain of 0.05 and 0.1 under a strain rate of 3×10-3 s-1. The structure evolution is characterized by the formations of c-axis extension twins and c-axis compression twins, and their intersections in various directions, followed by the appearance of fragmented structure. The gradual formation of very fine grains along the c-axis compression twins with increasing cumulative strain finally leads to a ultra-fine grained structure with an average grain size of about 80-150 nm. Low strain may promote the rapid formation of more amounts of mutually crossing twins due to orientation change from pass to pass. The ultra-fine grain evolution can be accelerated by increasing pass strain. The grain refinement mechanisms under cold multiple deformation were discussed in some details.
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