Effect Of Ca,Sr And Y On Microstructure And Properties Of Mg-Si-Zn Alloy

Because Mg₂Si can be easily formed by reaction of Si with Mg in magnesium alloys,Mg₂Si phase with high temperature strength becomes an important method of improving the high-temperature performance.But the primary and eutectic Mg₂Si under the condition of traditional casting are very coarse,which enables its application to be restricted in engineering,therefore the study on modification of the primary and eutectic Mg₂Si becomes an emphasis for research on the magnesium alloy with Si.By adding of Mg-Ca,Mg-Sr,Mg-Y master alloys to the Mg-4Si-4Zn alloy and using the elements of Ca,Sr,Y to modify the magnesium alloy,the modification of Mg-4Si-4Zn alloy has been performed,the changing rules of the solidified microstructure and phase in the magnesium alloy under the conditions of different modified elements and its content in the alloy and modified mode?single and composite modification?investigated,the modification effect and its mechanism of primary and eutectic Mg₂Si in the microstructure analysized.The research results show that there is a big difference between the optimal modification effect of different modification elements and content under single modification.After Y modification of Mg-4Si-4Zn alloy,the morphology of primary Mg₂Si is transformed from large dendrite to short-rod,the morphology of eutectic Mg₂Si from the complex multi-stroke Chinese character structure to the simple incoherent point bar.During the solidification of Mg-4Si-4Zn alloy,the solidification condition of primary and eutectic Mg₂Si can be changed by the elements of Ca and Sr,to modify them.The primary Mg₂Si can be transformed from large dendrite to small regular square block and the morphology of eutectic Mg₂Si from complex Chinese pattern to short point bar.The mechanical properties of the modified alloy increase with the increase of modification effect.The modification of the three elements are developed according to the order of hypo modification,modification and hyper modification.Under Ca-Y complex modification,compared with single Ca modification,the morphology of primary Mg2Si can be transformed from regular square to complex morphology with ravine holes.After Sr-Y composite modification,the morphology of primary Mg2Si is transformed from regular square to hexagon with regular holes,compared with single Sr modification.The results show that the mechanical properties of microstructure with the primary Mg₂Si with holes is greater than the regular square morphology of primary Mg₂Si.The relationship between the modification effect and content of Y under the complex modification is same as that of single Y modification.At the same time,the sizes of primary and eutectic Mg₂Si do not change and the morphology of eutectic Mg₂Si also not change.