Study On The Microstructure And Mechanical Properties Of Rare Earth Magnesium Alloys

Rare earth magnesium alloys with good casting performance,high temperature performance and mechanical properties,have a broad application prospect in the fields of automobile industry,aerospace,electronic products and national defense.Research of different rare earth elements,deformation and annealing process,understand the influence of rare earth elements,deformation and annealing process on the recrystallization behavior of magnesium alloys and the effect on texture,explore alloy microstructure evolution in annealing process,it is of great significance to improve the ability of plastic deformation of magnesium alloy and improve its comprehensive performance.In this thesis,we obtained pure Mg,Mg-Ce,Mg-Y and Mg-Gd bar through the vacuum smelting technology and hot extrusion.Microstructure and mechanical properties of extruded and annealing magnesium alloys were characterized by using OM,SEM,EBSD and X-ray.Results revealed the influence of rare earth elements and extrusion speed on microstructure,texture,and mechanical properties of extruded and annealing alloy.Furthermore,taking Mg-Y alloy as the research object,the evolution of different morphology grains of Mg-Y alloy and their influence on the microstructure of Mg-Y was discussed.From these investigations,the following conclusions can be drawn:(1)Mg-Ce alloy is similar to pure magnesium in microstructure,which is coarse equiaxed grain,and the average grain size is similar-Mg-Y alloy occurs incomplete dynamic recrystallization during extrusion process,and the extrusion microstructure is composed of fine equiaxed grains with dynamic recrystallization and long deformed grains without dynamic recrystallization.Mg-Gd alloy occurs complete dynamic recrystallization during extrusion process,and the average grain size was reduced greatly compared with that of pure magnesium.Compared with the texture of extruded pure magnesium,the texture intensity of Mg-Gd alloy is reduced obviously.The tensile mechanical properties data show that the tensile strength can be improved by adding Ce,tensile strength and elongation were improved by adding Y element,and tensile strength did not change much,but elongation was improved significantly by adding Gd.(2)Compared with the annealing pure magnesium,the annealing Mg-Ce alloy shows little change in average grain size and grain size distribution.The microstructure of the annealing Mg-Y alloy is mainly composed of non-recrystallized elongated grains which is formed during the extrusion deformation and fine recrystallized grains.The proportion of deformed grains decreases apparently in comparison with the as-extruded Mg-Y alloy.Annealing Mg-Gd alloy consist of fine uniform equiaxed grains.The texture intensity of annealing Mg-Y and Mg-Gd alloys reduced obviously compared with that of pure magnesium.The tensile mechanical properties data show that the tensile strength of annealing Mg-Ce alloy is improved,but the elongation is reduced,the tensile strength and elongation of annealing Mg-Y alloy are increased,the tensile strength of annealing Mg-Gd alloy is not changed much,but the elongation is improved obviously.(3)Microstructure evolution of high and low speed extruded Mg-Y alloy shows the same evolvement rule during annealing process.With the increase of annealing time,SRX occurs in grain boundaries and internal shear zones of deformed grains,and SRX grains divide the deformed grains into multiple regions.<01,10>direction of deformed grain is parallel to the extrusion direction,and the c-axis of the deformed grain rotates around the extrusion direction,but always perpendicular to the extrusion direction.Recrystallized grains are always widely distributed and oriented.The higher extrusion speed,the faster SRX during annealing process.