Study On Anti-wear Properties And Crack Damage Mechanism Of Rare-earth Magnesium Alloys Treated By Extrusion And Aging

In order to improve the poor mechanical properties and friction and wear resistance of magnesium alloys,On the basis of adding rare earth elements to pure magnesium to prepare new rare earth magnesium alloy materials,this topic takes pure magnesium,extruded rare earth magnesium alloy,extrusion aging treatment of rare earth magnesium alloy as the research object.The microstructure morphology,mechanical properties,anti-wear properties and surface crack damage mechanism of three kinds of materials were compared to evaluate the effects of two preparation processes on the structure,mechanical properties and anti-wear properties of rare earth magnesium alloys.The research is carried out by combining experiment and finite element simulation.New rare earth magnesium alloys were prepared by casting,extrusion and aging by adding Gd,Y,Zn and Zr to pure magnesium.It was found by X-ray diffractometer analysis and ultra-deep optical microscopy that the doping of rare-earth elements led to the generation of a large number of rare-earth alloy phases,and the grain refinement effect was more obvious after aging treatment.The modulus of elasticity of 43.9 GPa,55.2 GPa,55.8 GPa and hardness of 0.67 GPa,1.64 GPa,1.83GPa for the three materials were obtained by nanoindentation tests.The average friction coefficients of the three materials were 0.465,0.29 and 0.284,respectively,and the maximum wear depths were about 30μm,18μm and 16μm,respectively,and the wear rates were about 2.64×10^-3 mm³·N^-1·m^-1,1.6×10^-3 mm³·N^-1·m^-1 and 1.16×10^-3 mm³·N^-1·m^-1,respectively,obtained from the friction wear test.SEM images of the surfaces of the three materials after friction showed that the surface cracks were reduced and the crack lengths were significantly lower after hot extrusion and aging treatment.The yield strengths of 0.033 GPa,0.126 GPa and 0.151 GPa and the plastic strengthening moduli of 1.165 GPa,15.346 GPa and 18.035 GPa for the three materials were calculated by finite element simulation and combined with the method of volume analysis.Through the finite element method to analyze the material crack damage found that there is a large three-way stress on the surface of pure magnesium,resulting in crack sprouting and cracking in the Y and Z directions,forming a crack surface;a large X and Y stress at the tip of the crack;doping rare earth elements and after hot extrusion and aging treatment,the three-way stress gradient is significantly reduced.The following research findings were obtained from the study:adding rare earth elements and hot extrusion and aging process can significantly refine grain size,and the combination of solid solution strengthening and second phase strengthening synergistic effect leads to the mechanical properties and anti-wear properties of rare earth magnesium alloy materials are significantly improved.Compared with the hot extrusion process,the effect of aging treatment on the anti-wear performance of rare earth magnesium alloy materials is not obvious.In the friction process,the pure magnesium material fracture resistance is the worst,the material surface cracks sprout,and in the X,Y direction stress synergistic effect of the crack expansion phenomenon,the formation of composite crack.Doping with rare earth elements and hot extrusion treatment can effectively inhibit the crack extension behavior.After aging treatment,the material did not occur crack extension phenomenon,and the fracture resistance of rare earth magnesium alloy material was significantly enhanced.The research results of the project provide a more comprehensive theoretical support for the development and preparation process of new high-performance rare earth magnesium alloy materials,mechanical and anti-wear properties,and crack damage mechanism research.