Experimental investigation on microstructure and mechanical properties of gravity-die-cast magnesium alloys

Abstract

The influence of various alloying elements (i.e., Sn, Al, Si, Mm, Sc) with different quantities on the microstructure and mechanical properties of gravity die cast magnesium alloys are investigated. Experimental evidences show that the secondary dendrite arm spacing is increasing with the increase in Sn content from 5% to 8% in Magnesium alloy. Misch Metal (Mm) addition in Mg-5%Sn causes grain refinement (∼30%) and the shape of interdendritic second phase particles changes from rod/irregular geometry to feathery shape. In Mg-8%Sn-3%Al-1%Si alloy, α-Mg, Mg2Sn, Mg17Al12 and Mg2Si phases are identified. Addition of Al-Sc master alloy refines the grain size (∼12%) of Mg-8%Sn alloy. Solution heat treatment at 520 °C for 48–72 h leads to complete dissolution of Mg2Sn intermetallic for Mg-Sn alloys. During ageing of Mg-Sn alloys at 200 °C, discontinuous precipitation of Mg2Sn occurs at grain boundaries and their triple junctions at the initial stage and later they become coarse in nature. Tensile properties (i.e., YS, UTS and %EL) are improved after 100 h of aging for all alloys used compared with the cast alloys of same composition. Cast Mg-8%Sn-3%Al-1%Si alloy exhibits superior tensile properties as compared to cast Mg-5%Sn, Mg-8%Sn,Mg-5%Sn-2%Mm,Mg-8%Sn-3%(Al-Sc) alloys.