SIMA法制备AZ91半固态坯料枝晶衍变规律的研究

Microstructural Evolution during Semisolid State of AZ91 by Strain Induced Melt Activation Process

研究了应变诱发熔化激活法(SIMA)制备AZ91半固态坯料枝晶演变规律.挤压后,AZ91组织结构为白亮拉长的初生α相和分布在其间的黑色共晶相.由于变形不充分,在试棒中心垂直于挤压方向仍有较大的初生α相存在.575℃等温重熔过程中,首先发生再结晶,伴随液相向再结晶产生的晶界渗透,导致枝晶破碎.随着等温保温时间的增加,组织转变为细小的球状α相,均匀分布在液相中.等温保温10m in时,α相由于组织的球化和粗化过程而变得更为圆整粗大.

Thixotropic microstructure formation of AZ91 by Strain Induced Melt Activation Process（SIMA） was investigated in this study. After extrusion, the AZ91 shows a typical extruded structure comprising of brightly elongated area with dark area inbetween. There is a few big primary α-phase existing in the centre of transverse cross section due to the insufficient extrusion deformation. In partial remelting and isothermal holding at 575℃ , recrystallization occurs first in the strain hardened alloy. The initial liquid phase penetrates grain boundaries induced by recrystallization, causing fragmentation. With the increase of isothermal holding, the microstructure of extruded material evolve to fine and globular α-phase particles suspended in the liquid phase. After 10 minutes isothermal holding, α-phase particles become more globular and bigger due to spherodization and the coarsening of the microstructure.