The Reasearch On Microstructure And Mechnical Properties Of Mg-Zn-Sn-Al-X Wrought Magnesium Alloys

Wrought magnesium alloys exhibit higher strength than cast magnesium alloys.Being the weight reduction structural materials,wrought magnesium alloys have wide applications in the automotive,electronic and aeronautical industries.Researches on microstructure and properties of wrought magnesium alloys can not only lay the theoretical foundations for the development of novel wrought magnesium alloy but also offer the reliable theoretical basis for their safe design and reasonable usage.The Mg-Zn-Sn alloy system is a novel wrought magnesium alloy series,which has attracted more attention in recent years.In this paper,microstructure and properties of the hot-rolled and the as-aged Mg-Zn-Sn-Al-X magnesium alloys are investigated by optical microscope?OM?,micro-hardness,tensile testing,X-ray diffract analysis?XRD?,scanning electron microscope?SEM?,transmission electron microscope?TEM?and etc.It is aimed to offer the detailed experimental data and the theoretical basis for the development of low-cost high-performance wrought magnesium alloys.The research results are given below:?1?Effects of the Zn/Sn mass ratio?0.5,1 and 2?on microstructure and mechanical properties of the as-rolled Mg-xZn-ySn-2Al-0.2Ca?x+y=9wt%?alloys are systematically studied.With the increase of the Zn/Sn mass ratio,the average grain size and the volume fraction of twins in the direct rolling and the solution rolling samples exhibits a tendency of increasing firstly and then decreasing.The strength and the elongation of the direct rolling,the solution rolling and the solution rolling plus ageing sample exhibit the similar tendency with the increasing the Zn/Sn mass ratio.The Mg-4.5Zn-4.5Sn-2Al-0.2Ca alloy exhibits the best combined mechanical properties.?2?Effects of the Ca addition?0.2%,0.4%and 0.6%?on microstructure and mechanical properties of the as-rolled Mg-4.5Zn-4.5Sn-2Al alloys are systematically studied.The 0.2%Ca addition plays important roles in refining twins and DRX grains,increasing the volume fraction of twins and promoting precipitations.The RT ultimate tensile strength and the yield tensile strength of the as-rolled alloy with 0.2%Ca are increased to 379MPa and 266MPa respectively,while its elongation is decreased to7.1%.The minor Ca addition can increase the activation energy of the precipitates,delay the aging process,refine the ageing precipitations and inhibit the segregation of Mg₂Sn particles.The RT ultimate tensile strength,the yield tensile strength and elongation of the as-rolled alloy with 0.2%Ca are increased to 406MPa,284MPa and8.9%respectively;its ultimate tensile strength at 200?is increased to 170MPa,but its elongation is decreased to 42.9%.?3?Effects of the 0.1%Ti addition and the combined 0.1%Ti and 0.02%B addition on microstructure and mechanical properties of the as-rolled Mg-4.5Zn-4.5Sn-2Al alloys are studied.The Ti addition and the combined Ti and B addition reduce the rolling formability of alloys,refine the DRX grains,reduce the volume fraction of twins and the microstructural homogeneity of the as-rolled alloy.However,both have no obvious improvement on the tensile strength,but lead to the reduction in elongation.Moreover,the Ti addition and the combined Ti and B addition accelerate the aging process by reducing the activation energy of precipitates,but bring about no obvious precipitation strengthening.?4?Effects of the combined 0.1%Ti and 0.2%Ca addition on microstructure and mechanical properties of the as-rolled Mg-4.5Zn-4.5Sn-2Al alloys are studied.The combined 0.1%Ti and 0.2%Ca addition further refine DRX grains,reduce the volume fraction of twins.The RT ultimate tensile strength,the yield tensile strength and elongation of the as-rolled alloy with the combined 0.1%Ti and 0.2%Ca addition are increased to 338MPa,237MPa and 11.9%respectively.The combined 0.1%Ti and 0.2%Ca addition can delay the aging process by improving the activation energy of precipitates.The RT ultimate tensile strength,the yield tensile strength and elongation of the as-aged alloy with the combined 0.1%Ti and 0.2%Ca addition are increased to358MPa,251MPa and 9.5%respectively.