| Magnesium alloy sheet has broad application prospects in aerospace,rail transit,electronic products and other fields.However,the poor formability at room temperature and strong anisotropy of the magnesium alloy sheet under the conventional process which have limited its wider application in industry.In this paper,through the systematic process of electromagnetic stirring casting-extrusion forming tube-compression-shear unfolding the sheet,explore the short process production process of high-performance magnesium alloy sheet,the process parameters are optimized through the study of the structure,performance evolution and deformation mechanism during sheet forming.The tensile strength,elongation and hardness of the AZ31 magnesium alloy sheet prepared by the above method are 200 MPa and 16.8%,respectively.Firstly,by analyzing the difference between the initial ingot under different conditions(natural solidification,electromagnetic stirring,electromagnetic stirring-quenching),it is found that the second phase in the structure after electromagnetic stirring-quenching was dissolved in the matrix,and there are twins and small angle grain boundary in the grain.The mechanical properties of the alloy are improved due to the obstruction of the twins grain boundaries and the low angle grain boundaries.The tensile strength and elongation of AZ31 prepared by electromagnetic stirring after quench are 200 MPa and 16.8%.It is found that the mechanical properties of the tube extruded(25.3×400°C)by the electromagnetic stirring-quenching ingot are better than natural solidification,but the texture difference after extrusion is not obvious.The main reason for the difference in mechanical properties is due to the difference in initial grain size,and the dynamic recrystallization delay effect makes the mechanical properties of the electromagnetic stirring-quenching tube after extrusion better than the natural solidification after extrusion.Secondly,the electromagnetic stirring-quenching ingots are subjected to isothermal extrusion with an extrusion temperature of(300°C?350°C?400°C)and an extrusion ratio of(8.2?10.6?25.3)to forming magnesium alloy tube,respectively.Through the analysis of the mechanical properties of the extruded tube and the observation of the structure.The results show that: with the increase of extrusion temperature,the grain size and the structure uniformity increases,the tensile strength and hardness decrease,but due to the decrease of the number of grain boundaries the elongation increases.The recrystallization mode is transformed from continuous dynamic recrystallization(CDRX)to discontinuous dynamic recrystallization(DDRX)with the increase of extrusion temperature.The texture exhibits the texture component of grain plane orientation?ED direction and c axis?TD;with the extrusion ratio increases,the grains of AZ31 magnesium alloy tube become fine,and the degree of dynamic recrystallization increases,the grain size of AZ31 magnesium alloy tube becomes smaller,and the recrystallization growth is restrained with the increase of extrusion ratio,but the increase of deformation degree makes the texture concentrate and strength increase,and the increase of grain refinement and structure uniformity leads to the increase of strength and toughness of magnesium alloy.When the extrusion parameter is 25.3×400°C,the best comprehensive mechanical properties are obtained.The tensile strength,elongation after fracture and hardness of magnesium alloy tube are 270 MPa,23% and 65 HV respectively.Finally,Shear bands and twins can be introduced into the sheet by compression-shear,which will deflect the grain orientation and reduce the texture strength,resulting in weakened anisotropy of the sheet.however,the strain-hardening caused by the introduction of the shear bands reduces the elongation.Through research on different annealing parameters it is found that after complete annealing at 400°C×4h,the tensile strength,elongation and hardness of AZ31 magnesium alloy sheet were 255 MPa,30% and 60.3HV,respectively. |
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