Effect Of Upsetting And Extrusion Deformation On The Microstructure And Mechanical Properties Of Mg-RE Alloy

With the increasing development of China’s aerospace industry and national defense industry,large key load-bearing parts for major equipment in aerospace and national defense are in urgent need of high-performance,low-energy consumption methods and materials,and integral forming has been favored by researchers as one of the "low-carbon","green" and economic processing methods.The size of the casting bar required for integral forming is relatively large,but due to the limited diameter of the casting,small-diameter castings have a more uniform organization due to their smaller composition segregation,resulting in products with better performance.Therefore,a large high-diameter ratio is needed to ensure the integral forming of the main load-bearing parts through large plastic deformation of the open billet.For this reason,this paper proposes a large height-to-diameter ratio upsetting and extrusion process,which can achieve a single large plastic deformation,a single time to obtain a large strain,to get a better strengthening effect,and to achieve short process billet making.In this paper,Mg-9Gd-4Y-2Zn-Zr(wt.%)alloy was investigated by optical microscopy(OM),scanning electron microscopy(SEM),electron backscatter diffraction(EBSD),tensile testing machine and other research methods.The effects of deformation temperature and pressdown amount(Working distance of convex die during upsetting)on the microstructure and mechanical properties of the alloy after one time of large height-to-diameter ratio upsetting and extrusion process were investigated,and the tissue evolution process and toughness mechanism of large-diameter-ratio upsetting were studied.This provides a theoretical basis for further research on large height-to-diameter ratio cyclic upsetting and extrusion.The results show that the grain size becomes smaller,the dynamic recrystallization rate increases and the granular β-phase increases as the deformation temperature and the amount of press-down increase.After one large diameter ratio header extrusion,the weave of the alloy did not appear the typical extrusion weave,but with the increase of deformation temperature and depression amount,the tendency of the weave tending to the typical extrusion weave was more obvious,and the weave strength also gradually increased.The ultimate tensile strength(UTS)and elongation(EL)both increase with increasing temperature and with the increasing amount of depression.The tensile yield strength(TYS)increased with the increase in temperature.460°C tensile yield strength increased with the increase of depression amount.420°C and440°C tensile yield strength and depression amount did not evolve linearly,tensile yield strength decreased and then increased with the increase of depression amount.60% depression amount(The working distance of the convex die during upsetting is 60% of the initial bar length110mm)had the worst tensile yield strength,and 70% depression amount(The working distance of the convex die during upsetting is 70% of the initial bar length 110mm)had the highest tensile yield strength.The best mechanical properties of the alloy were obtained at460°C deformation temperature and 70% depression corresponding to one pass of large high diameter ratio header deformation with the ultimate tensile strength of 368.84 MPa,yield strength increase of 151.11 MPa and elongation of 17.96%.The weave reinforcement plays a dominant role in the large height-to-diameter ratio upsetting and extrusion process deformation.Solid solution strengthening has no effect on the differences in the strength of the alloy under different deformation parameters,second phase strengthening and fine grain strengthening have a smaller effect on the differences in the strength of the alloy,while weave strengthening plays a larger role in the differences in the strength of the alloy under different deformation parameters.