AZ31B镁合金应变诱发半固态组织观察

Microstructure of Semi-solid AZ31B Magnesium Alloy Through Strain-induced Meltactivation Method

采用AZ31B镁合金挤出材，在573K进行28％-30％预变形加工，然后在863—893K经过不同保温时间进行等温球化处理，观察了试样不同区域的组织，考察了温度及保温时间对组织的影响，得到了具有圆整固相颗粒的半固态组织．实验结果表明：适当提高球化处理温度，有利于加速球化过程，以获得细小圆整半固态组织；延长保温时间固相分数降低，但幅度不大，并发生颗粒不规则化；在同一个试样上，由于部位不同，变形程度不同，所得半固态材料的固相率不同．讨论了半固态组织的形成机理，分析认为预变形后，半固态组织形成过程包括再结晶、晶粒长大阶段，受溶质、空位扩散控制的半固态组织形成阶段，受液-固界面张力作用的固相颗粒圆整化阶段．开始形成半固态组织阶段，扩散占主导地位，在进一步球化过程中，界面张力占主导地位．

A semi-solid microstructure of AZ31 B magnesium alloy containing spherical solid particles was studied. This material was subjected to a series of spheroidizing treatments for various holding times at 863 - 893K after being compressed by 28% - 30% in length at 573K. The effects of heating temperature and holding time on microstructures were studied. It was found that increasing the heating temperature could accelerate the spheroidizing process, resulting in small spherical semi-solid microstructures. With a longer holding time, the solid content slightly changed and the solid particles became irregular. Solid content is different in different section in the same specimen. The semi-solid microstructure forming mechanism has been discussed in this paper. It is considered that the semisolid microstructure forming process included three stages： the re-crystallization and the growth of grain stage ; the semisolid microstructure forming stage controlled by the diffusion of solute and vacancy ; the conglobating of solid particle stage controlled by the liquid-solid boundary tension. The diffusion played an important role in the original stage and the boundary tension reacted on the later spheroid process.