Microstructure And Mechanical Properties Of Wrought LAZ832-0.5Y Alloy

Magnesium-lithium alloys,also known as ultralight alloy,possess the lowest density as structural metallic material so far.The addition of lithium can also make huge contribution to the plasticity of magnesium alloy,which will hence get a great improvement in machining deformation ability.Compared with ordinary magnesium alloy,magnesiumlithium alloys possess lower density,higher specific strength and stiffness,and greater machining deformation ability,which show a great prospect of application in fields such as aerospace,military and electronic industry.However,the absolute strength of magnesium-lithium alloys is relatively low,which restricts the further application of magnesium-lithium alloys.Further research on the strengthening of ultralight Mg-Li alloy is of great significance in application in aerospace field.This study was undertaken to evaluate the effect of deformation on the microstructure and mechanical properties of Mg-8Li-3Al-2Zn-0.5Y(wt%)alloy.The Mg-8Li-3Al-2Zn-0.5Y alloy was prepared by casting and then deformed by extrusion and rolling with several processing parameters,in order to optimize the deformation processing.The results indicate that the as-cast Mg-8Li-3Al-2Zn-0.5Y is composed of ?-Mg phase,?-Li phase and precipitated intermetallic compounds with two different shapes,particle-like with smaller size and irregular-like with larger size.Microstructure analysis results implied that the smaller particles are some mixture of AlLi and MgLi2 Al,and the irregular-like phase is Al2 Y.Dynamic recrystallization(DRX)happened during extrusion process,and ?-Li phase got significantly refined.Dispersive intermetallic phases were broken into small particles and distribute evenly in the matrix.As extrusion ratio increases from 1(as-cast)to 25,?-Mg phase becomes sharper but distributes most uniformly in the specimen with the ratio of 16.As extrusion temperature increases from 100? to 300?,?-Mg phase gets spherical and the precipitated phases decrease obviously.After rolling process,the as-rolled Mg-8Li-3Al-2Zn-0.5Y alloys present anisotropic structure in 3 dimensions.The ?-Mg phase got elongated in both rolling direction(RD)and transverse direction(TD),with a larger extent of deformation in the rolling direction.As-cast Mg-8Li-3Al-2Zn-0.5Y alloy presents superior mechanical properties,with UTS of 200 MPa and elongation of 13.9%.After extrusion process,the strength and elongation of the alloy are both significantly improved,due to grain refinement and precipitation dispersion.As the extrusion ratio increases from 4 to 25,the tensile properties first improve and then decline.The alloy with the extrusion ratio of 16 exhibits the highest yield strength,ultimate tensile strength and elongation of 214 MPa,243 MPa and 41%.As the extrusion temperature increases from 100? to 300?,the strength of the alloy gets improved from 238 MPa to 250 MPa and the elongation declines from 28% to 16%.After rolling processing and as the rolling strain accumulated,the strength of the alloy was notably improved in 2 directions,the highest of which reached 250 MPa,while the elongation ratio declined,due to strain hardening and precipitate dispersion.The tensile properties of the as-rolled alloys in the RD,no matter the YS,UTS or the elongation ratio,are higher than those of TD due to the significant anisotropy in the HCP ?-Mg phase.After aging treatment from 100? to 200?,the hardness of both as-extruded and asrolled alloys obviously declined in a short time and after that gradually stayed stable.The final hardness of both as-extrude and as-rolled alloys decreases with the accumulation of time and the increase of aging temperature.