Si对喷射成形AZ91镁合金微观组织的影响

Effect of Si on microstructure of spray formed AZ91 Mg alloy

在保护气氛中采用喷射成形技术制备AZ91和AZ91+2.0%Si镁合金,采用OM、SEM、XRD及TEM等技术分别对合金的微观组织进行观察和分析。结果表明:与相同成分的铸造镁合金相比,喷射成形技术显著细化合金组织;喷射成形沉积态AZ91镁合金具有均匀、细小的等轴晶组织,平均晶粒尺寸约为17μm,离异共晶β-Mg17Al12相在晶界的偏析被有效改善;对于喷射成形AZ91+2.0%Si镁合金,喷射成形过程中高的冷却速度抑制了Mg2Si相的长大,细小的Mg2Si相呈现为近球形或多边形态,与基体结合良好且弥散分布,并可以作为α-Mg异质形核核心,使合金组织得到充分细化。

AZ91 and AZ91＋2.0%Si Mg alloys were prepared by spray forming technology in protecting atmosphere. The microstructures were studied by optical microscopy （OM）, scanning electron microscopy （SEM）, X-ray diffractometry （XRD） and transmission electron microscopy （TEM）. The results show that the microstructures of spray formed magnesium alloys are fine-grained compared with as-cast ones with the same compositions. The microstructure of as-sprayed AZ91 Mg alloy is uniform, fine and equi-axed. The average size of particles is about 17μm, and the nonuniform precipitation of divorced eutectic β-Mg17Al12 is effectively improved. In the microstructure of as-sprayed AZ91＋2.0%Si, the high cooling speed during spray forming process restrains the growth of Mg2Si. Mg2Si existing in the fine grains, presents polygonal or near round shape, which uniformly distributes and can be the heterogeneous core of α-Mg, so the spray formed AZ91 Mg alloy is sufficiently refined by Si added.