中文摘要：

考察了直流电流密度、等温温度及等温时间对AZ91D镁合金半固态组织的影响，对电流影响组织演变的机理进行了探讨．实验结果表明：当等温温度和等温时间一定时，随着电流密度的增加，初生相变得圆整，初生相的尺寸有所减小．但电流密度过高时，初生相尺寸有所增加．直流电流可以加速半固态等温处理的组织演化过程，明显改善枝晶球化效果．直流电流增加扩散激活能，增大溶质原子的扩散系数，促进溶质原子的扩散，从而加速半固态等温过程的组织演化；直流电流作用下的电迁移效应、Joule热效应和Peltier效应都将促进枝晶的熔断和球化．

英文摘要：

The influences of direct current density, heating temperature, and holding time on the microstructure evolution of magnesium alloy AZ91D during semi-solid isothermal heat treatment were studied, and the related mechanism was also discussed. When heating temperature and holding time are constant, with the increment of current density the primary phase becomes small and smooth. But if current density is too high, the primary grains become coarser. Direct current can accelerate the course of semi-solid isothermal heat treatment and improve globular effect of dendrites obviously. It is proposed that the activation energy is increased by direct current, so the diffusivity of solute atoms is increased, which accelerates the microstructure evolution. The effect of electromigration, Joule heat and Peltier heat caused by direct current will promote remelting and globuling of dendrites.