添加0.5%富铈混合稀土AZ91D镁合金半固态组织的形成

半固态浆料的固相颗粒尺寸、形态和分布主要取决于熔化过程中液相的形成与演化过程。采用添加0.5%富铈混合稀土来改善AZ91D镁合金的铸态组织,研究在半固态等温热处理中的组织演变以及非枝晶组织制备与控制的机理。结果表明:稀土合金化处理可促进初生相在等温热处理过程中由枝晶向粒状晶的转变,可获得更加细小、均匀的球状固相颗粒,并且其粗化速度较慢。半固态等温热处理过程中,整个系统处于熔化和结晶的动态平衡,铸态组织中枝晶根部高溶质浓度区或系统的温度、浓度起伏是固相颗粒内液相形成的内在和外在条件。

Effect of rare earth 0.5% addition on semi-solid microstructural evolution of AZ91D alloy

The size,shape and distribution of solid phase particle in semi-solid slurry lie mainly on the formation and evolution of liquid phase during remelting of the alloy.As-cast microstructure of AZ91D alloy was improved with rare earth(RE) 0.5% addition.The microstructural evolution was studied during semi-solid isothermal treatment,and the mechanism of fabrication and controlling of non-dendritic microstructure was discussed.The results indicate that the transformation from the primary phase to spheroid particle is accelerated,and the fine and symmetrical spheroid grains are gained by rare earth(RE) alloying during semi-solid isothermal treatment of magnesium alloy AZ91D.It is proposed that the microstructure in specimen is in dynamic equilibrium state of melting and crystallizing during semi-solid isothermal treatment.The high solute concentration area at dendrite root of the as-cast alloy,or the temperature/ composition fluctuations is the internal or external conditions of liquid formation in solid particle.