二次加热过程中半固态AZ31镁合金的显微组织演变

利用波浪形倾斜板振动技术制备AZ31镁合金半固态坯料,获得较为理想的球形或近球形晶粒组织。结果表明:随二次加热温度的升高和保温时间的延长,半固态组织中的液相体积分数增大,固相逐渐长大并球化;AZ31镁合金580℃和610℃时二次加热组织均不适合半固态触变成形;适合触变成形的二次加热最优工艺为590℃保温40～60 min、或者600℃保温30 min;此条件下获得的平均晶粒直径为58～61μm,固相率为87%(体积分数)左右。晶格扩散机制对二次加热原子扩散起主导作用,是造成合金固相颗粒尺寸变化的根本原因;固液界面张力是造成颗粒形状球形或近球形变化的重要原因。

Microstructure evolution of semisolid AZ31 magnesium alloy during reheating process

AZ31 magnesium semisolid billets were prepared by a self-designed wavelike vibration sloping plate device,and an ideal globular or near-globular microstructure can be obtained by wavelike vibration sloping plate technique.The results show that,with the increase of reheating temperature and the prolongation of holding time,the liquid fraction in semisolid microstructure increases,and the solid phase grows gradually and spheroidises.The reheating microstructures at 580 ℃ and 610 ℃ are not suitable for thixoforming.The optimum reheating process parameters suitable for thixoforming are 590 ℃ for 40-60min or 600 ℃ for 30 min,under which the average grain diameter is 58-61 μm and solid fraction is about 87%.The lattice diffusion resulting in the variation of grain size is the dominant atomic diffusion mechanism of reheating.The solid-liquid interfacial tension results in the variation of globular or near-globular shape.