Mg-2Zn-0.5Y镁合金半固态等温处理过程中的微观组织演变

Microstructure evolution of semisolid Mg-2Zn-0.5Y alloy during isothermal heat treatment

摘要:

本文研究了挤压Mg-2Zn-0.5Y合金在半固态等温处理过程中的微观组织演变规律。结果表明：挤压态的Mg-2Zn-0.5Y合金包含α-Mg，I相和W相三种物相，并且平均晶粒尺寸为7μm。在温度为793K的半固态等温热处理过程中，晶粒不断长大，直到保温时间达到4min时才出现液相。随着等温处理温度和时间的增加，α-Mg固相颗粒不断长大，并且逐步被液相分离；同时，出现在晶界的液相与颗粒内部的液滴都在不断地增多。研究还发现，当固相率较高的时候，晶粒间的合并机制与固相颗粒再熔化机制同时起主导作用；然而当固相率较低的时候，Ostwald熟化机制是主要的粗化机制，同时也可以观察到晶粒间的合并。

Abstract:

In this paper, microstructure evolution of extruded Mg-2Zn-0.5Y alloy in semisolid isothermal heat treatment process was investigated. The results show that in the alloy there are α-Mg, I-Phase and W-phase, and the average grain size of α-Mg is 7 μm. During isothermal heat treatment at 793K, the grain continued growing and no liquid phase appeared until isothermal holding time arrived at 4min. With isothermal temperature raising and holding time increasing, solid α-Mg grains in the alloy were gradually growing and separated by liquid phases. Meanwhile, the liquid phase locating both at the grain boundaries and in the grain interior significantly increased. It is also found that at higher solid fractions, particle coarsening mechanism and solid particle remelting mechanism both play major roles. While at lower solid fractions, Ostwald ripening is the major mechanism and coalescence of adjacent particles could still be observed.