Research On Texture And Microstructure Evolution Of Rotary Backward Extrusion Mg-13Gd-4Y-2Zn-0.5Zr Alloy

Mg-Gd-Y-Zn-Zr alloy has become one of the most promising alloy systems in high-strength heat-resistant magnesium alloy due to its excellent high-temperature mechanical properties.It is increasingly used in aviation,aerospace,weaponry and other fields.However,due to its low casting properties,plastic deformation is required to improve performance.The Mg-13Gd-4Y-2Zn-0.5Zr cup was formed by Gleeble-3500 thermal simulation torsion system.The effects of different forming parameters(deformation temperature,axial extrusion speed and circumferential equivalent strain rate)on the microstructure and mechanical properties of the alloy were investigated.Tissue observation and phase analysis using optical microscopy(OM),X-ray diffractometry(XRD)and scanning electron microscopy(SEM).Characterization of the texture and mechanical properties of the alloy by electron backscatter diffraction(EBSD)and microhardness tester.The research shows that:(1)The influence of forming temperature on the texture and mechanical properties of the rotary backward extruded Mg-13Gd-4Y-2Zn-0.5Zr cup is greater than the axial extrusion speed and the circumferential equivalent strain rate.At ??5%(95%confidence),the forming temperature has a significant effect on the forming force,Schmid factor,average grain size and hardness value;the axial extrusion speed has a significant influence on the forming force.(2)On the observation surface perpendicular to the extrusion direction,Mg-13Gd-4Y-2Zn-0.5Zr cup-shaped parts formed by rotary backward extrusion,the grains from the outside to the inside are gradually refined,the degree of dynamic recrystallization is gradually increased,the grain size is gradually reduced,the distribution of the LPSO phase is more uniform,the degree of kink is gradually increased,and the generation of DRX grains is extended from the grain boundary portion to Inside the grain,the hardness in the deformed area is more evenly distributed in the radial direction.During the rotary backward extrusion process,the Schmid factor of the base surface is below 0.5,and the stress value required for crystal slip is higher.(3)When the forming temperature is 450 0 C,the axial extrusion speed is 0.05 mm·s-1,and the circumferential equivalent strain rate is 0.01 s-1,and in the deformation region of the rotary backward extruded Mg-13Gd-4Y-2Zn-0.5Zr cup,the degree of kink of the LPSO phase and the degree of dynamic recrystallization deformation are balanced,the dynamic recrystallization area fraction reached the maximum value,and ultrafine crystal grains with a grain size of 0.4 ?m were obtained,and arranged into a DRX crystal chain in the direction of rotation.The crystal grains showed random orientation and the texture strength was weak,on the pole figure.The cylindrical texture close to the extrusion direction can be observed,the minimum texture strength is 2.958 MPa,and the hardness has a minimum value of 104.33 HV.