Effect of Al Addition on Microstructure and Properties of Az91/Cao Alloy

The effects of further addition of Al element (AZ91-0.7CaO-1Al (wt.%), AZCA) on microstructure, corrosion resistance and mechanical property of AZ91-0.7CaO (AZC, wt.%) alloy were investigated with the comparison of commercial AZ91 (AZ91) alloy. The result showed that the addition of Al could further reduce the grain size to 31.41 μm on the basis of refinement from 109.38 μm to 50.35 μm by adding CaO particles in AZ91 alloy. The bulky β-Mg17Al12 was refined significantly after adding CaO particles and then a semi-continuous β-Mg17Al12 and more numerous supersaturation Al formed after further addition of Al. Meanwhile, the volume fraction of second phases decreased after adding CaO particles but then increased after further addition of Al. The supersaturation Al and semi-continuous β-Mg17Al12 can effectively promote the formation of protective films on AZCA alloy surface and reduce the annual corrosion rate to 8.3 mm/y in long-term salt spray corrosion. Although the higher second phase density somewhat affects the fatigue life of AZCA alloys, the microhardness, tensile and compressive strength was also further increased due to the fine-grain strengthening and second phase strengthening with the addition of Al