Microstructure And Mechanical Properties Of Centrifugal Cast ZW61and AZ91Magnesium Alloy

In this paper, a new Mg-6wt.%Zn-1wt.%Y-0.5wt.%Zr （ZW61） alloy was preparedby centrifugal casting and metal mould casting respectively. The as-cast microstructureand mechanical properties of the alloys were investigated comparatively. The resultsshow that the microstructure of centrifugal casting magnesium alloy is significantlyrefined, and its mechanical properties are improved. Then the microstructure and phasecomposition of ZW61alloy were investigated through SEM，XRD and EDX. It wasfound that the matrix phase of both the alloys is α-Mg phase, and the second phase ofZW61alloy are composed of I-phase （Mg₃Zn₆Y） and W-phase （Mg₃Zn₃Y₂）. Theelement distribution of the centrifugal casting is more uniform than the metal mouldcasting alloy. According to the ImageJ software analysis, the area fraction of thesecond phase in the centrifugal casting alloy is lower than that in the metal mouldcasting alloy. In centrifugal casting process, the eutectic transformation of L→α-Mg+W and eutectoid transformation of W→α-Mg+I were suppressed, which results inthe reduced content of I-phase and W-phase, and form a solidification microstructurewith the saturated primary phase consisting mainly of α-Mg phase. The centrifugalcasting alloy possesses more plastic features than the metal mould casting alloy andthe elongation ratio is improved.Mg-9wt.%Al-1wt.%Zn-0.35wt.%Mn（AZ91） alloy was prepared by centrifugalcasting, metal mould casting and sand casting respectively. The microstructure andmechanical properties of the alloys were compared. The results show that themicrostructure of centrifugal casting magnesium alloy is significantly refined, and itsmechanical properties are obviously better than the other two kinds of castings. Thenthe microstructure and phase composition of AZ91alloy were investigated throughSEM，XRD and EDX. It was found that the solidification microstructure has the samephase composition, with the matrix phase of α-Mg phase, and the second phase ofβ-Mg₁₇Al₁₂phase and AlMn phase. The element distribution of the centrifugal castingis more uniform than both the metal mould casting alloy and the sand casting alloy.The three kinds of castings possess obvious plastic features after heat treatment, and the elongation ratio is higher than the as-cast castings.