Study On Ingredient Design And Microstructure, Mechanical Properties Of High Strength Mg-Al-Sr Alloy

The study of Magnesium alloys has been taken more and more attention, especially strengthen and elongate of Magnesium alloys.The present work has investigated the effect of different content of Al and Sr, heat treatment on the microstructure and mechanical properties at room temperatures, by experimental methods such as optical microscopy (OM), scanning electron microcopy (SEM) with energy dispersive X-ray analyses (EDAX), microhardness tester and electronic tensile tester.The results showed that: AM series Magnesium alloys are composed ofα-Mg solid solution, Mg₁₆Al₁₂ phase and Al₈Mn₅ phase by casting in steel mould. The number of Mg₁₇Al₁₂ phase increases with the increasing of Al content. Some of Mg₁₇Al₁₂ phase grow up into discontinuous networks. The ultimate tensile strength increases and then decreases. The elongation ratio unceasingly reduces. But the microhardness of alloy increases with increasing of Al content. When Sr element has been added, the alloy is composed ofα-Mg solid solution, Mg₁₇Al₁₂ phase, Al₄Sr phase and Al₈Mn₅ phase. When Sr content is invariable, the number of Mg₁₇Al₁₂ phase increases with the increasing of Al content. But Al₄Sr phase does not change with the increasing of Al content. The ultimate tensile strength increases and then decreases. The elongation ratio unceasingly reduces. But the microhardness of alloy increases with increasing of Al content. When Al content is invariable, the number of Al₄Sr phase increases with the increasing of Al content. But Mg₁₇Al₁₂ phase does not change with the increasing of Sr content. With increasing of Sr content, the ultimate tensile strength increases, and the elongation ratio keeps stably, but the microhardness of alloy increases and then decreases. All the grains of alloys are fined by casting in the copper mould. AM series Magnesium alloys are composed ofα-Mg solid solution and Al₈Mn₅ phase, however AM90 alloy has a few amount of Mg₁₇Al₁₂ phase. With increasing of Al content, the ultimate tensile strength and the microhardness of alloy increase, but the elongation ratio decreases. When Sr element has been added, the alloy is composed ofα-Mg solid solution, Al₄Sr phase and Al₈Mn₅ phase. When Sr content is invariable, the ultimate tensile strength and the microhardness increase, but the elongation ratio decreases straight with increasing of Al content. When Al content is invariable, the ultimate tensile strength increases and then decreases, and the elongation ratio do not change, but the microhardness of alloy increases and then decreases with increasing of Sr content. Mg-x%Al-0.5%Sr is investigated by heat treatment both casting in steel and copper mould. It is found that segregation of alloy is disappeared. But the microhardness decreases in different kind of level. Only the microhardness of Mg-9%Al-0.5%Sr which has been treated with aging is little bigger than that of as cast.