电磁搅拌过程中镁合金半固态浆料初生相颗粒的团簇行为

Agglomerating behavior of primary solid particles in magnesium alloy semisolid slurry during electromagnetic stirring

利用旋转电磁场搅拌制备AZ91D镁合金半固态浆料，在570-600℃间不同温度下浇注金属型试样，观察和分析不同固相率铸件的微观组织。结果表明：较低固相率伍≤25％）铸件由d-Mg等轴晶和β-Mg17A112相组成基体组织，初生固相颗粒以松散的聚团形式分散其中；而在相对较高固相率（36％≤fs≤45％）铸件中，浇注温度降低，初生相颗粒数目的剧增和浆料黏度的增大使得初生相颗粒在电磁搅拌形成的黏性剪切作用下相互间发生摩擦和挤压塑性变形，从而在高温条件下焊合形成紧密的团簇结构，且聚团中初生相颗粒间的晶界表现为低能量的直线型晶界。

AZ91D magnesium alloy semisolid slurry was prepared using rotating electromagnetic stirring, and the molded samples were obtained at different pouring temperatures from 570 ℃ to 600 ℃, then the microstructures were characterized in detail and linked to the corresponding solid volume fraction. The results indicate that the incompact structure agglomerating a few primary solid particles, which disperses in the matrix consisting of a-Mg equiaxed dendrite and network distributed Mg17A112 precipitates, is observed within structures of low solid fraction （fs） no more than 25%. Meanwhile, for the samples with a higher solid fraction, i.e. 36%≤fs≤45%, due to the reduction in the casting pouring temperature, increasing both the number of primary solid phase and the viscosity of slurry, brings the interaction among the primary particles within vigorously stirring melt, and thus causing slide, friction and plastic deformation between or among the neighboring solid particles. So the primary particles are welded together to form clusters at high temperature and exhibit low energy line-type crystal boundaries.