Microstructural evolution during partial remelting of AM60B magnesium alloy refined by MgCO_3  

作　　者：陈体军 马颖 王瑞全 李元东 郝远 

机构地区：[1]Key Laboratory of Gansu Advanced Nonferrous Metal Materials,Lanzhou University of Technology

出　　处：《Transactions of Nonferrous Metals Society of China》2010年第9期1615-1621,共7页中国有色金属学报（英文版）

基　　金：Project(G2007CB613706) supported by the National Basic Research Program of China

摘　　要：AM60B magnesium alloy was refined by MgCO3 and its microstmcturat evolution was investigated during partial remelting. The results indicate that MgCO3 is an effective grain refiner for AM60B alloy and can decrease the grain size from 329 pm of the unrefined alloy to 69 μm. A semisolid microstructure with small and spheroidal primary particles can be obtained after being partially remelted. The microstructure evolution can be divided into four steps： the initial rapid coarsening, structure separation, spheroidization and final coarsening. Correspondingly, these four steps result from the phase transformations of β→α, α＋β→L and α→L, α→L and two reverse reactions of α→L and L→α, respectively. One spheroidal primary particle in the semisolid microstmcture usually originates one dendrite in the as-cast microstructure. The variation of primary particle size with holding time does not obey the LSW law, Dt^3-Do^3=Kt, after the semisolid system is in its solid-liquid equilibrium state. Longer heating duration makes the primary particles more globular, but it makes their size larger at the same time.AM60B magnesium alloy was refined by MgCO3 and its microstructural evolution was investigated during partial remelting.The results indicate that MgCO3 is an effective grain refiner for AM60B alloy and can decrease the grain size from 329 μm of the unrefined alloy to 69 μm.A semisolid microstructure with small and spheroidal primary particles can be obtained after being partially remelted.The microstructure evolution can be divided into four steps:the initial rapid coarsening, structure separation, spheroidization and final coarsening.Correspondingly, these four steps result from the phase transformations of β→α, α+β→L and α→L, α→L and two reverse reactions of α→L and L→α, respectively.One spheroidal primary particle in the semisolid microstructure usually originates one dendrite in the as-cast microstructure.The variation of primary particle size with holding time does not obey the LSW law, Dt3?D03=Kt, after the semisolid system is in its solid-liquid equilibrium state.Longer heating duration makes the primary particles more globular, but it makes their size larger at the same time.

关 键 词：AM60B alloy THIXOFORMING microstructure evolution phase transformation partial remelting 

分 类 号：TG292[金属学及工艺—铸造]