Observation On Hot Extrusion Deformation And Recrystallization Mechanism Of Mg-Zn-Gd Alloy

At present,due to its low density,good recycling performance,and excellent physical properties,magnesium alloys have received increasing attention not only in the aerospace and military applications but also in the automotive and 3C industries.Mg-Zn series alloys are commonly used magnesium alloys with good comprehensive properties.Adding Gd element can reduce stacking fault energy and promote dynamic recrystallization during thermal deformation.The occurrence of dynamic recrystallization during thermal deformation plays an important role in the coordinated deformation.To improve the plasticity of magnesium alloys and broaden the application fields,it is necessary to deeply study the recrystallization mechanism during the hot deformation process.During the hot extrusion process,due to the strong three-dimensional stress,a series of defects in the processed ingot structure can be eliminated,and the grains can be refined to improve the mechanical properties.On the one hand,dynamic recrystallization during thermal deformation plays an important role in coordinated deformation,on the other hand,it also affects the structure,mechanical properties,and texture of extruded products.Therefore,this article focuses on the hot extrusion deformation and recrystallization mechanism of Mg-1Zn-1Gd alloy.Firstly,the hot extrusion test of Mg-1Zn-1Gd alloy with an extrusion ratio of 20 and extrusion temperature of 420 ? was carried out,and the recrystallization behavior of Mg-1Zn-1Gd alloy during extrusion was studied and analyzed through DEFORM 3D simulation software,metallographic microscope,scanning electron microscope and electron backscatter technology.The research results show that due to the three-way stress in the extrusion process,the grains are significantly refined,and the uniformity is significantly improved.The average grain size decreased from 84.89 ?m in the as-cast state to 7.13 ?m.Through the analysis of different extrusion deformation zones,it is found that as the amount of deformation increases during the extrusion process,recrystallization gradually increases.In the hot extrusion process,continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX)coexist.Secondly,hot extrusion experiments were conducted with the same extrusion ratio(20),different extrusion temperatures(420°C,450°C,480°C).and with the same extrusion temperature,different extrusion ratios(20,30,40).Through the study of structure and properties,it was found that under the same extrusion ratio,when the extrusion temperature increased,the average grain size gradually increased from 7.13?m(420?)to61.93?m(480?).At lower extrusion temperatures,the proportion of recrystallization is greater than 45%,while at higher extrusion temperatures,the proportion of recrystallization is only 13%.As the extrusion temperature increases,the tensile strength first increases and then decreases,while the elongation first decreases and then increases.When the extrusion temperature is 420?,the grain refinement effect is obvious as the extrusion ratio increases.Finally,an electrochemical test was performed on the Mg-1Zn-1Gd alloy.Through the study of the microstructure,dynamic potential polarization curve and EIS curve,it was found that the more complete the recrystallization,the better the corrosion resistance.Therefore,the completely recrystallized structure reflects the best corrosion resistance.When the morphology of the structure is completely recrystallized,the corrosion resistance decreases as the extrusion ratio increases,and the extrusion temperature increases.