Study On Simulation Optimization And Microstructure And Properties Of New Extrusion Processes For High Strength And Toughness Mg-Gd-Y-Zn-Mn Aolly

In recent years,magnesium alloys have attracted widespread attention at home and abroad due to their advantages such as low density,high specific strength,and good damping performance.It is hoped to replace steel,aluminum alloys and other materials.Extrusion is one of the most common and most advantageous plastic deformation processes for magnesium alloys.Because the alloy is subjected to triaxial compressive stress during extrusion,it can improve the deformation ability of the alloy,so it is particularly suitable for magnesium alloys forming.Therefore,based on the conventional extrusion process,it is of great significance to explore new extrusion processes for forming complex magnesium alloy parts or to further improve the magnesium alloy microstructure and properties.This subject first used DEFORM finite element simulation software to numerically simulate the backward extrusion process of high-strength and toughness Mg-Gd-Y-Zn-Mn alloy variable cross-section profiles,and the effects of different extrusion process parameters(the extrusion temperature,the extrusion speed and the maximum wall thickness of the profile)on the deformation process of the alloy were analyzed.The best backward extrusion process parameters were obtained:the extrusion temperature is 470~oC,the extrusion speed is 0.1mm/s and the maximum wall thickness of the profile is 10mm,which can provide the theoretical guidance for the subsequent preparation of variable cross-section profiles.Then,through finite element numerical simulation,the differential temperature extrusion process of high-strength and toughness Mg-Gd-Y-Zn-Mn alloyφ25mm bar was studied,and the forming temperature field,the equivalent strain field,the equivalent stress field and the forming force of the alloy during deforming under different process parameters(the original temperature of the blank and the original temperature of the die were different)were analyzed.The optimal differential temperature extrusion process parameters were obtained,that is,the original temperature of the blank is 510~oC,the original temperature of the die is 390~oC,and the extrusion speed is 0.5mm/s,and the numerical simulation results of the conventional extrusion processes with extrusion temperatures of 420~oC and 510~oC were compared and analyzed.420~oC is currently the best conventional extrusion temperature for the alloy to obtain better mechanical properties.Finally,the optimized differential temperature extrusion test and the conventional extrusion tests at 420~oC and 510~oC of the alloy rods with a diameter ofφ25mm were performed.The results show that the surface quality of the alloy rods after differential temperature extrusion is still good when extruding at a faster speed,and the microstructure of the alloy after differential temperature extrusion is small and completely dynamic recrystallized grains,while the alloy after 420~oC conventional extrusion shows the bimodal-grained microstructure.lamellar LPSO phases are precipitated inside some dynamic recrystallized grains of all extruded alloys,while relatively few lamellar LPSO phases are precipitated in the alloy after differential temperature extrusion.Only rare earth texture exists in the alloys after differential temperature extrusion and 510~oC conventional extrusion,while the 420~oC conventionally extruded alloy shows only strong basal texture due to the deformed non-recrystallized grains.The alloy after differential temperature extrusion and peak aging exhibits better comprehensive mechanical properties.Its tensile strength,yield strength,and elongation are 492MPa,314MPa,and 10.5%,respectively.This is the result of the interaction of fine grains,block-shaped and lamellar LPSO phases andβ’phases.