Preparation And Process Optimization Of Ultra-fine Grain Structure Of New Mg-Y-Nd-Zr Alloy

Magnesium alloys have low strength and have a limited slip system due to the HCP crystal structure,and have poor processing properties at normal temperatures.In this paper,a new type of Mg-Y-Nd-Zr alloy was developed for these problems in magnesium alloys,And the ECAP deformation of different passes was carried out at 400°C.The influence of ECAP deformation pass on the microstructure and mechanical properties of the alloy was studied systematically.The optimization of the previous ECAP process was also carried out.The as-rolled magnesium alloy was prepared.The influence of rolling temperature on the microstructure and properties of the alloy was studied systematically.Then the ECAP deformation of the alloy in different conditions and different passes was carried out,and the ultrafine grained structure was successfully prepared and systematically studied.The relationship between microstructure and texture evolution and mechanical properties of rolled alloys.The new Mg-Y-Nd-Zr alloy is mainly composed of Mg matrix phase and Mg₂Y phase.After ECAP deformation,the grain of Mg-Y-Nd-Zr alloy is obviously refined,and with the increase of extrusion pass,the structure becomes fine and uniform,and the grain refining effect is best after 4passes;some Mg₂Y phase precipitates after ECAP deformation;and with the increase of the extrusion pass,the proportion of the small-angle grain boundary decreases,and the large-angle grain boundary increases.At the same time,after the ECAP deformation,the strength and orientation of the new Mg-Y-Nd-Zr alloy texture are both With some changes,the texture strength is the weakest at 4 passes,and it changes from a slanted texture to a strong basal texture at 6 passes,and the Schmid factor tends to 0.The mechanical properties show that the grain refinement is greater than the softening and strengthening of the texture.With the increase of ECAP deformation pass,the mechanical properties of Mg-Y-Nd-Zr alloy alloy have been improved.The as-cast Mg-Y-Nd-Zr alloy could successfully perform multi-pass rolling at 400?,and the grain is remarkably refined,and the typical rolling base texture is formed in the alloy.The strength of the alloy is obviously improved,but the plasticity is significantly reduced.It is found that the ECAP deformation of the rolled Mg-Y-Nd-Zr alloy is studied.The as-cast Mg-Y-Nd-Zr alloy has the best ECAP deformation grain refinement at 340?,and the average grain size is reduced from 7.64?m to 1.94?m in the as-rolled state,and there is no cracking on the surface.The second phase of Mg-Y-Nd-Zr alloy is reduced,the texture strength is weakened,and the typical rolling texture is transformed into ECAP shear texture.The grain orientation also changes significantly,and the grain orientation changes.Compared with the as-rolled alloy,the elongation of the as-rolled alloy after ECAP deformation is significantly improved,but the strength is reduced.Finally,the microstructure changes,texture evolution and mechanical properties of the rolled Mg-Y-Nd-Zr alloys with different ECAP deformations are discussed.The results show that the grain of Mg-Y-Nd-Zr alloy is obviously refined after multi-pass ECAP deformation,and the ultrafine-grained magnesium alloy is obtained after four passes of deformation,and the second phase of rolled Mg-Y-Nd-Zr alloy gradually decreases with the increase of ECAP deformation pass,and is in a stable state.these stable second phases have a good coherent relationship with the matrix,which also serves to limit grain growth.After the low-pass ECAP deformation of the rolled Mg-Y-Nd-Zr alloy,the proportion of the small-angle grain boundary increases remarkably,and the large-angle grain boundary decreases.As the ECAP deformation pass increases,more small-angle grain boundaries in the alloy are transformed into high-angle grain boundaries,and recrystallization is more complete.Moreover,the grain orientation has also changed significantly,the texture strength is weakened,the Shmind factor is increased,and the“texture softening”effect occurs.At the same time,the work-hardening of the as-rolled alloy in the ECAP process is eliminated,so that the fine-grain strengthening effect is not obvious,the yield strength change is inconsistent with the Hall-Petch relationship,but the plasticity is significantly improved,and the strength of the as-rolled alloy after ECAP deformation is higher.The rolled alloy decreased,but it was significantly improved compared to the as-cast alloy,and the tensile strength increased to 238 MPa.