轧制及退火处理对铸轧态AZ31镁合金组织的影响

Effect of rolling and heat treatment on microstructure of roll-cast AZ31 alloy

利用金相显微镜、SEM及TEM对铸轧态AZ31镁合金在不同轧制及退火状态下的显微组织进行了研究。结果表明：铸轧态AZ31合金在420℃进行轧制变形时，合金以动态再结晶为主，且随着轧制变形量的增加，等轴再结晶晶粒尺寸逐渐变小。变形量为40％时，析出相得到破碎，晶界也变得更加清晰，此外，局部区域还出现了等轴再结晶晶粒；当变形量增大到90％时，合金以细小的等轴再结晶晶粒为主，晶粒尺寸约为10μm，且TEM观察可知合金基体内分布有较多细小的析出相，部分粗大再结晶晶粒边界附近还分布有一些由于动态再结晶而形成的细小晶粒。铸轧态AZ31合金在420℃轧制变形90％后再进行不同温度的退火，可知随温度升高再结晶晶粒长大明显，到450℃退火时，晶粒长大到20～30μm，对此退火样进行300℃温轧，基体内出现大量的孪晶和亚晶组织。

The microstructure of roll-cast AZ31 alloy under rolling and annealing conditions were studied by means of optical microscope, SEM and TEM. The results show that as rolling at 420%, dynamic recrystallization occurs in the alloy, and with the increase of deformation amount, the size of recrystallized equiaxed grains formed in the roll-cast AZ31 alloy are gradually refined. When deformation amount is 40%, some precipitated phases are broken, its original grain boundary obviously becomes sharper, and fine equiaxed recrystallized grains are observed in some local areas. As deformation amount increasing to 90%, fine equiaxed recrystallized grain prevails in the microstructure with the grain size of 10μm. A large number of fine precipitated phases are observed in the alloy deformed 90% by TEM, and some fine grains generated by dynamic recrystallization distribute around the boundary of coarse recrystallized grains. After annealing at different temperatures, the size of the recrystallized grains increases with the increase of annealing temperature. As annealing temperature reaching 450%, the grain size is about 20 - 30μm. After rolling at 300%, lots of twins and subgrains can be found in the matrix of the alloy.