AZ91镁合金的SIMA法半固态组织特征

Microstructural characteristics of semisolid AZ91 magnesium alloy based on SIMA process

研究了挤压态AZ91镁合金的SIMA法半固态组织演变。结果表明: 挤压合金为以α Mg再结晶等轴晶为主相, 与极少量细粒状成串分布于α Mg基体上的Mg17Al12颗粒组成的两相组织, 基体中存在大量的大角度亚晶及高密度的位错缠结。在二次加热过程中, 原子扩散通道多, 晶界液化及颗粒球化所需的加热温度低, 等温时间短。565℃等温5 min,即可获得固相率为57%, 颗粒平均直径为58μm、形状圆整、分布均匀的半固态组织。等温5 min后, 半固态颗粒发生长大, 其长大机制为Ostwald熟化。

The microstructural evolution of semisolid AZ91 magnesium alloy by SIMA process was investigated. The microstructure of as-extruded Mg alloy is mainly composed of α-Mg recrystallized grains and a small quantity of (Mg_(17)Al_(12)) particles distributed in Mg matrix as a cluster. There are a great deal of large angle subcrystals and high density dislocations in α-Mg grains. Due to many of atom diffusion channels during secondary heating, the heating temperature required for liquidizing of grain boundaries and spheroidizing of grain surfaces is low and the holding time becomes short. Holding 5min at 565℃, the homogeneous semisolid microstructure with solid fraction of 57% and mean grain size of about 58μm is obtained. After holding 5min, the semisolid grains become coarse and the coarsening mechanism is Ostwald ripening.