Effect Of Sn Additions On Microstructure And Mechanical Properties Of Mg-Zn-Al Alloy

Magnesium alloys with excellent performance have received increasing attention in the past decades for their potential applications in the transportation,communication and aerospace industry.Therefore,the development of magnesium alloys with high performance play a key role in the industrialization magnesium alloys.However,the strength of magnesium alloys is still relatively low which limits their application and becomes the urgent problem to be solved.Precipitation hardening is one of the most effective methods to improve the strength of Mg alloys.Therefore,the research on precipitates is important to design new Mg alloy and improve the strength of Mg alloy.In this thesis,the effect of Sn additions on the microstructure and mechanical properties of Mg-8Zn-4Al-0.5Mn(wt.%)alloys is studies.The microstructure was characterized using SEM and TEM,and the hardness and mechanical properties were tested by Vivtorinox hardness tester and tensile machine.Combined with the microstructural characterization results,the relationship between the microstructure and mechanical properties was discussed.It is found that Sn additions can improve the as-quenched hardness value of Mg-8Zn-4Al-0.5Mn alloy,which is mainly attributed to fine grain size and Mg2Sn particles with several hundred nanometer formed during solid-solution treatment,caused by the additions of Sn.But the hardness increment from the as-quenched condition to the peak-aged condition is almost identical.The hardness value of peak-aged Mg-8Zn-4Al-0.5Mn-3Sn alloy during isothermal ageing at 200? is 93HV.The precipitates in peak-aged Mg-8Zn-4Al-0.5Mn and Mg-8Zn-4Al-0.5Mn-3Sn alloys are mainly rhombic and lath ? phase(Mg21(Zn,Al)17),and the orientation relationship between the ? phase and the magnesium matrix is such that(102)?//(1010)?[010]?//[2110]?Sn additions can improve the strength of Mg-8Zn-4Al-0.5Mn extrusion alloy.With 3wt.%Sn addition,the tensile yield strength of Mg-8Zn-4Al-0.5Mn increase from 145 MPa to 200 MPa,and the ultimate tensile strength increase from 213 MPa to 230MPa.The increased number density of chain-like intermetallic particles and fine grains are responsible for the strength enhancement.