The Research On Semi-solid Microstructure And Properties Of Mg-6Zn-xTi Alloy

Magnesium alloy has the advantages of low density,high specific strength,good casting performance and reproducibility.And now magnesium alloy is widely used in the automotive,aerospace,electronic communications and other fields.The effect of Ti additional（wt%）on the microstructure and mechanical properties of alloys were studied by optical microscope（OM）,scanning electron microscope（SEM）,X-ray diffraction（XRD）and mechanical property test.The semi-solid microstructure of the alloys was prepared by the method of semi-solid isothermal-treatment,non-dendritic microstructure evolution process and the effects of Ti content to the non-dendritic semi-solid microstructure are studied of Mg-6Zn alloys.And the mechanism is discussed soon.The testing shows that Mg-6Zn binary alloy hasα-Mg and MgZn₂ phases.Andα-Mg,MgZn₂,TiZn₁₆6 and TiZn₃ phases can be found in the Mg-6Zn-0.3Ti alloy.For the Mg-6Zn-0.5Ti alloy,there are justα-Mg,MgZn₂ and TiZn₁₆6 phases.With the increase of Ti addition,the alloy-containing 0.8Ti hasα-Mg,MgZn,TiZn₁₆6 and Mg₇Zn₃ phases.With the addition of Ti,the UTS and EL are both influenced highly and change by the form of increasing firstly and then decreasing.The Mg-6Zn-0.5Ti alloy has the highest UTS（212 MPa）and EL（11.2%）.With the addition of Ti,the hardness is influenced highly and change by the form of increasing firstly and then decreasing.The Mg-6Zn-0.5Ti alloy shows the best hardness（62.94HV）.There are cleavage fracture and quasi-cleavage fracture of Mg-6Zn-xTi alloys.Considering the comprehensive mechanical properties,The Mg-6Zn-0.5Ti alloy is chosen to undergo homogenizing,solution and aging treatment.Heat treatment process to obtain the optimal solutionized at 340℃+12h,aging at 160℃+10h、20h、30h、40h、50h.The tensile strength has reached 308MPa,hardness of 77.69HV.And the fracture analysis shows that the Mg-6Zn-0.5Ti alloy mainly solvability cleavage fracture.The content of Ti has a positive affect to the non-dendritic microstructure in the isothermal treatment process.The best semi-solid process of Mg-6Zn alloy is of preserve heat at 580℃for 30min and the particle size,shape factor and solid fraction are 71μm、1.6 and64.5%,respectively.When the content of Ti is 0.3%,30min at 590℃,the particle size,shape factor and solid fraction are 60μm、1.2 and 64.0%,respectively.When the content of Ti is0.5%,40min at 620℃,the particle size,shape factor and solid fraction are 59μm、1.2 and65.0%,respectively.When the content of Ti is 0.8%,40min at 610℃,the particle size,shape factor and solid fraction are 70μm、1.4 and 69.0%,respectively.