AZ31镁合金板材低温双向反复弯曲变形及退火过程的组织演化

STRUCTURE EVOLUTION OF AZ31 Mg ALLOY SHEET DURING BIDIRECTIONAL CYCLIC BENDING AT LOW TEMPERATURE AND SUBSEQUENT ANNEALING

对AZ311镁合金热轧板材在423 K进行了双向反复弯曲变形及523 K退火处理,利用OM及SEM/EBSD技术研究了该工艺过程中的组织和织构演化规律.结果表明,孪生为其主要的变形机制,随着变形道次的增加,靠近表面的晶粒中不断地累积孪生变形,并最终被高密度的孪晶分割细化;而中部组织变化不大,仅有少量孪晶产生;样品趋向于形成两边孪晶密度大、中间孪晶密度小梯度变化的双面对称组织.6道次变形的样品在523 K退火1000 s后,表层晶粒发生了完全静态再结晶,平均晶粒尺寸由46μm细化至10μm左右,在板材两边各形成了约为1/4板厚的细晶层,且该区域的组织较为稳定.此外,其室温延伸率也由19.01%提高到了24%左右,但抗拉强度变化不大,这是由于板材两边的晶粒细化和织构弱化共同作用所致.

In this work,microstructure and texture evolution in the sheets of Mg alloy AZ31 was studied by means of bidirectional cyclic in-plane bending at 423 K followed by annealing at 523 K.The deformed and subsequent annealed microstructures were investigated by OM and SEM/EBSD examinations.The results showed that twinning is the dominant deformation mechanism. With the increase of deformation pass,more and more twins were produced in the grains near the surfaces of the sheets and finally these grains were serially divided up by twinning intersections. But only a few twins were formed in the grains of the middle of the sheets due to relatively lower strain. Finally,a gradient structure with high-density twins in the regions near the surfaces and,in contrast, lower density ones in the center of the sheets were induced.After 6 pass bending at 423 K followed by a subsequent annealing at 523 K,the average grain size near the surfaces was reduced to about 10μm from the original size of 46μm due to operation of static recrystallization at twin intersections and compression twins.Particularly,the relative intensity of the strong texture developed in the sheets was severely weakened by repeated bending,and this led to an increase of fracture elongation from 19.01% to about 24%with little change of tensile strength.