电磁搅拌工艺参数对半固态AZ91D 镁合金组织的影响

研究了电磁搅拌工艺参数对半固态AZ91D合金组织的影响规律。结果表明：电磁搅拌条件下半固态AZ91D合金组织的固相颗粒为蔷薇状或粒状α—Mg，随电磁搅拌功率的增大，蔷薇状形态逐渐消失，固相颗粒形态趋于粒状和圆整；在实验范围内，随电磁搅拌电源频率的增大，半固态AZ91D合金组织中固相颗粒形态越来越圆整。这主要是由于电磁搅拌条件下半固态AZ91D合金组织的形成机理是以枝晶臂熔断为主，而在高频率下的电磁搅拌过程中，在搅拌室产生的集肤效应使得表面和中心出现宏观温度差，从而加强了固相颗粒随流场运动时的温度起伏，最终加速了枝晶的熔断。

Effect of Electro-magnetic Stirring Process Parameters on the Microstructure of Semi-solid AZ91D Alloy

The effect of electro-magnetic stirring process parameters on the microstructures of semi-solid AZ91D alloy was studied. The results show that the shape of solid particles in the alloy was rosette-like or granular. With the stirring power increasing, the rosettelike particles disappear gradually, and solid particles get more and more spherical. A higher power makes the solid particles of the alloy more spherical, because the main evolution mechanism of microstructure of the alloy is the dentritic arm melting method. A higher frequency introduces a skin effect on the stirred semi-solid slurry, which makes a temperature difference between the edge and the center. The slurry under electro-magnetic stirring takes a secondary flow besides the horizontal rotating flow, which makes the slurry move from the edge to the center in cycles. This secondary flow results in a promotion of dendritic arm being melted away from the dendrite grains by the large temperature fluctuation.