变形量对AZ91镁合金SIMA半固态组织形成的影响

Effects of Extrusion Ratio on Semisolid Microstructure Formation of AZ91 Alloy

研究了形变量、形变组织对AZ91镁合金半固态组织形成的影响。结果表明,形变镁合金由分布于变形条纹间的细小αMg再结晶等轴晶及极少量Mg17Al12颗粒组成。随变形量的增加,晶界增多,晶粒更加细小,晶内位错密度增大,形变合金的畸变储备能增大。在半固态加热及等温过程中,首先在高畸变晶界发生共晶体液化。大形变合金晶界畸变能高,发生液化时间早,而且与小形变合金相比,其半固态晶粒更加细小,形态圆整,组织更为均匀。565 ℃等温5 min后,发生半固态晶粒的逐渐长大。随等温时间延长,挤压比对晶粒尺寸的影响减弱。

The extrusion ratio, microstructure and their effects on semisolid microstructure formation of deformed AZ91 Mg alloy are investigated. The results show that the microstructure of deformed alloy consists mainly of α-Mg recrystallized grains and small amounts of Mg17Al12 partials distributed in Mg matrix as a cluster. With the rise of extrusion ratio, the grain boundaries increase, the grain is refined and the dislocation density within grains increases remarkably. It indicates the alloy is in the state of high distortion energy storage. In the heating and holding for semisolid state process, the eutectic distributed in grain boundaries remelts firstly. The alloy with larger extrusion ratio is easy to remelt so that the fine, granular semisolid microstructure can be obtained. If holding time at 565°C is more than 5 minutes, the semisolid grains will become coarsening, and with the prolonging of holding time, the effects of extrusion ratio on grain size are not remarkable.