Effect Of Plastic Deformation On Microstructure And Mechanical Properties Of Mg-14Li-1Zn Alloys

Mg-Li alloy is the lightest metallic engineering material.It has many advantages such as high specific strength,specific stiffness,good plastic deformation and high energy particle penetration resistance.However,the low strength and poor corrosion resistance limit the application range of Mg-Li alloy.In order to prepare a high-strength and high-toughness ultralight Mg-Li alloy.This thesis focuses on the low mechanical properties of Mg-Li alloy.Zn element was added into Mg-Li alloy to prepare Mg-14Li-1Zn alloy by argon shielded melting,and then Mg-14Li-1Zn alloy was rolled and extruded to change the microstructure and improve the mechanical properites.The microstructure and mechanical properties of the alloys were characterized by metallographic microscope(OM),scanning electron microscope(SEM),energy-dispersive spectrometer(EDS),X-ray diffraction(XRD),and transmission electron microscope(TEM),Nano indentation test and tensile test and other testing methods.As-cast Mg-14Li-1Zn alloy is based on ? phase,a large number of spherical ? phases are precipitated along the grain boundary which leads to intergranular fracture of Mg-14Li-1Zn alloy during tensile test.The mechanical properties of the as-cast Mg-14Li-1Zn alloy are poor.The ? phase is difficult to be removed by heat treatment.It is found that the ? phase with bcc structure is different from the ? phase with hcp structure in magnesium alloys.The hardness of ? phase is 1.2GPa,higher than that of ? matrix(0.75GPa).The Mg-14Li-1Zn alloy exhibits fibrous microstructure after cold rolling with different amount of deformation,and the mechanical properties of the alloy are improved obviously.Dynamic recrystallization occurs at room temperature when the total rolling reduction is larger than 70%.Obvious equiaxed grains can be observed in some regions.The grain size is 2-10?m,and the tensile strength reaches the maximum value of 212 MPa.Vickers hardness is 60.12 HV.With the further increase of deformation,the tensile strength of the alloy decreases slightly to 210 MPa due to the occurrence of dynamic recovery recrystallization.But the plasticity of the alloy is greatly improved,the elongation is greatly increased to 19.8%.In order to solve the problem of poor formability of cold-rolled Mg-14Li-1Zn alloy slab,the hot rolling and extrusion process were adopted.It was found that,as for the slab prepared by 50% reduction at 300°C,after 80% reduction of cold rolling,the sheet has the best comprehensive mechanical properties with tensile strength of 238 MPa,Vickers hardness of 67.70 HV and elongation of 14.2%.Therefore,reasonable blank making process can effectively improve the microstructure and mechanical properties of Mg-14Li-1Zn alloy.