Effect Of Particle Micro-forging Process And Annealing On Microstructure And Properties Of AZ31 Magnesium Alloy Sheet

Magnesium alloy sheet has broad application prospects in 3C products,automobiles and other fields.However,magnesium alloy sheet prepared by traditional processes such as rolling and extrusion has strong basal texture,strong anisotropy and poor formability at room temperature,which greatly limits the development of magnesium alloy sheet.In this paper,the surface of AZ31 magnesium alloy rolled plate was micro forged with steel shot particles by cold spraying equipment,and annealed to explore the evolution law of microstructure and properties of magnesium alloy plate in the process of particle micro forging and annealing.By optimizing the process parameters,the basal texture and anisotropy of magnesium alloy were weakened,and magnesium alloy plates with better strength and toughness were prepared.The main research contents and results are as follows:The cold spraying equipment is used to carry out particle micro forging of AZ31 magnesium alloy rolled plate with different gas pressures(0.5MPa,1MPa,1.5MPa)and different gas temperatures(25℃,250℃,400℃).Through the analysis of the microstructure and mechanical properties of the plate,it is found that in the process of particle micro forging,the surface of magnesium alloy plate will extend around the crater formed by steel shot impact,produce plastic deformation,introduce residual stress and work hardening,and produced a large number of twins;with the increase of gas pressure and gas temperature,the speed of steel shot particles will increase,which makes the plastic deformation of magnesium alloy plate more intense,the introduced residual stress increases,the degree of work hardening becomes more serious,the hardness and tensile strength increase,and the elongation decreases gradually.Under the conditions of gas pressure 1MPa and gas temperature 250℃,the surface morphology of magnesium alloy plate processed by particle micro forging is the most flat,without bending,and has better comprehensive mechanical properties.The tensile strength is 262.02 MPa,the elongation is 9.2%,and the hardness is 110.2HV.The magnesium alloy sheet processed by particle micro forging under the conditions of gas pressure of 1MPa and gas temperature of 250℃ was annealed at different holding times(15min,30 min and 60min)and temperatures(200℃,250℃ and 300℃)respectively.Through the analysis of the microstructure and mechanical properties of the sheet,it was found that with the increase of holding time,the recrystallization was more sufficient,the storage energy was more released,and the proportion of small angle grain boundary decreased gradually,{0001} basal texture tends to be scattered;the dislocation density decreases,the grain grows gradually,and the microstructure uniformity decreases,resulting in the decrease of tensile strength and hardness;the release of stress and the reduction of the number of grain boundaries make the elongation increase first,but the continuous extension of holding time will reduce the uniformity of grain and reduce the elongation.With the increase of annealing temperature,the recrystallization rate increases,the storage energy is released faster,and the proportion of small angle grain boundary decreases;the tensile strength and hardness of the plate decrease gradually,and the elongation increases first and then decreases.After annealing at 250℃ and holding time of 30 min,the plane anisotropy coefficient △r of granular micro forged magnesium alloy plate is0.06,which is lower than that of the original rolled plate by 0.14,the anisotropy is weakened and the comprehensive mechanical properties are the best.The tensile strength is 232.42 MPa,the elongation is 25.1% and the hardness is 77.9HV.At room temperature,the cylindrical drawing experiments of magnesium alloy rolled annealed sheet and particle micro forging annealed magnesium alloy sheet were carried out respectively.The results show that the rolled annealed sheet is broken,and the shape of the sheet after particle micro forging annealed is good without fracture,indicating that the room temperature drawing formability of magnesium alloy sheet is improved after particle micro forging and annealing.