ECAP And Strengthen-Plasticization Behavior Of Super-Light LA141 Mg-li Alloy

In recent years,the rapidly growing automotive and aerospace industries have demanded new and lightweight materials,and Mg-Li alloy have been favored as the least dense metal structural materials.In particular,the ultra-light LA141 Mg-Li alloy is a BCCβphase at room temperature,which makes it have good plastic deformation ability.However,the strength of the alloy is low,resulting in limited application.Therefore,it is of great significance for the development and application of LA141Mg-Li alloy to explore an effective deformation process and heat treatment process parameters,so that the plasticity is at least unchanged or improved while the strength is improved.In this study,the LA141 Mg-Li alloy was subjected to large plastic deformation by equal channel angular pressing(ECAP)and equal channel angular pressing-rolling composite technology(ECAP+RL),and annealed at different temperatures to study different deformation processes and The effects of annealing temperature on the phase composition,grain size,fracture morphology and mechanical properties of the test alloy were analyzed,and the room temperature grain refinement mechanism and its strengthening mechanism were analyzed.The main findings are as follows:(1)The grain size of the original LA141 Mg-Li alloy is about 65um.The grain size is remarkably refined with the increase of the ECAP deformation pass.The grain size after 2 and 3 passes is about 12.5um and 10um respectively.After E rolling,the ECAP sample structure is stretched into strips,and the grains appear oriented.As the amount of reduction increases,the long strips are gradually refined to become fibrous.(2)The optimum annealing process parameters for ECAP samples after 2 passes and 20%after rolling were 210℃×1h.The 2pass ECAP sample was finely equiaxed with a grain size of about 5~10um after annealing at 210°C×1h;the ECAP sample after 20%rolling was annealed at 210℃×1h,and the grain size was about Is an equiaxed crystal of 10~15um;(3)After the original LA141 magnesium-lithium alloy sample was extruded 2times in ECAP,the yield strength(R_e),tensile strength(R_m)and elongation(A)of the sample were 170MPa,195MPa,and 24.2%,compared with the original state.The increase of 44.1%,38.3%,and 120%.ECAP specimens after rolling 20%were annealed at 210℃×1h,the R_e,R_m and A of the sample were 157MPa,197MPa,and28%,respectively,which were 33%,39.7%,and 155%higher than the original state.(4)The R_e,R_m and A of the ECAP samples after rolling 20%were 172MPa,190MPa,and 17.3%,respectively,which were 47.5%,34.8%,and 57.3%higher than the original state.ECAP specimens after rolling 20%were annealed at 210℃×1h,the R_e,R_m and A of the samples were 145MPa,210MPa and 23.8%,which were 23%,48.9%and 116.4%higher than the original state,respectively;(5)The SEM observation of the tensile fracture morphology of the alloy at room temperature shows that there are a large number of dimples in the fracture of the alloy under each process,which indicates that the fracture mechanism of the alloy is ductile fracture.However,the sample of ECAP extrusion is twice at 210℃×1h.After annealing,the shape and distribution of the fracture surface of the sample are uniform,the depth is deep and the shape tends to be equiaxed,indicating that the stress state of the sample when fracture is uniform strain.