Microstructure Design And Strengthening-toughening Mechanism Of Multiscale-structured Alloys

Mg has excellent mechanical properties such as light weight,high specific strength and specific stiffness,but its absolute strength is low and its plasticity is poor,so it is significant to improve the strength and plasticity of magnesium alloy by different methods.Rare earth elements Gd and Y were added to mg to improve the basic properties of the material,and then the microstructure was controlled by Surface Mechanical Attrition Treatment(SMAT)combined with heat treatment process.Mg-8Gd-3Y alloy and Mg-8Gd-7Y alloy were prepared in order to find a more potential alloy for strengthening and toughening.The results show that after solution treatment,the dendrite segregation was eliminated completely,and the second phase of Mg₅(Gd,Y)precipitated.After tensile test at room temperature,it was found that the yield strength and tensile strength of Mg-8Gd-7Y alloy in solution and hot rolled state were higher than those of Mg-8Gd-3Y alloy,but the elongation after fracture was relatively lower than that of Mg-8Gd-3Y alloy.Mg-8Gd-3Y alloy after hot deformation was selected as the research object.After SMAT,from the grinding surface to the inside of the structure,it is divided into severe deformation area,medium deformation area and matrix area,and the thickness of them were 300?m,300?600?m,and 600?m respectively.The aging hardening behavior of different layers after SMAT was studied.It was found that SMAT can greatly shorten the time to reach the hardness peak,and the hardness value of the material was distributed from the grinding surface to the matrix.The yield strength and tensile strength of SMAT Mg-8Gd-3Y alloy reached 220MPa and 264MPa respectively,but the elongation decreased from 4.4%to 1.4%after hot rolling.After high temperature annealing(500?×15min),dynamic recrystallization occurred in the microstructure of SMAT Mg-8Gd-3Y alloy,and equiaxed recrystallization grains appeared,with the grain size distributed along the depth direction.After aging treatment for 0?16h,it was found that the three layers reached the hardness peak at 8h.After annealing after aging,elongation was increased from 1.6%to 10.4%,and the tensile strength finally reached 244MPa.Figure 51,Table 6,Reference 88.