Grain Refinement And Texture Evolution Of AZ31 Magnesium Alloy Processed By Repetitive Continuous Welding Extrusion

Magnesium alloys have many advantages,such as high specific strength and stiffness,high dimensional stability,good damping and shock absorption performance,and have wide application prospects in the field of lightweight.However,because of the densely arranged hexagonal structure,the current plastic processing methods have their limitations.In this paper,an innovative processing method,continuous welding extrusion,is proposed.Taking AZ31 magnesium alloy as the research object,the continuous welding extrusion forming of AZ31 magnesium alloy is simulated and analyzed by using Qform finite element simulation software.Subsequently,by means of tensile test,electron backscatter diffraction(EBSD),scanning electron microscopy(SEM)and micro-structure analysis,the evolution of microstructure and properties of AZ31 magnesium alloy after repeated continuous extrusion and repeated continuous welding extrusion was investigated.In order to improve the comprehensive properties of AZ31 magnesium alloy synergistically,and promote the commercial application of AZ31 magnesium alloy.The main results are as follows:(1)The numerical simulation of AZ31 magnesium alloy rod continuous welding and extrusion was carried out,and the temperature field distribution,equivalent stress distribution,equivalent strain distribution,radial velocity distribution and time-load curve were obtained.The simulation results show that the highest temperature of metal flow occurs in the welding chamber during continuous welding and extrusion of AZ31 magnesium alloy rod.In the plastic deformation region of the die cavity,the distribution of equivalent stress and strain is not uniform.The maximum equivalent stress occurs in the welding chamber.The maximum equivalent strain also occurs in the welding chamber and extends downward,forming a strong linear equivalent strain area in the die cavity.In the process of continuous welding extrusion,the extrusion force decreases slightly after reaching a higher value in the initial stage,and then increases gradually to a peak value as the continuous welding extrusion process proceeds,and the continuous welding extrusion reaches a steady state stage,where the extrusion force fluctuates up and down.(2)After single pass continuous extrusion,the average grain size decreases from76.6 ?m to 55.9 ?m,and then increases with the increase of extrusion passes.In addition,compared with conventional extruded magnesium alloys,the pole density ofmagnesium alloys by continuous extrusion in each pass is more dispersed and the strength is reduced.(3)The mechanical properties of AZ31 magnesium alloy increased after single pass continuous extrusion.After that,with the increase of extrusion passes,the mechanical properties of magnesium alloy decrease gradually.After single pass continuous extrusion,the mechanical properties of the alloy increase,mainly because the effect of fine grain strengthening exceeds the effect of texture softening.(4)The average grain size of AZ31 magnesium alloy decreased significantly from20.3 ?m to 4.4 ?m after two passes continuous welding and extrusion.The texture of base plane changed from parallel to ED direction after conventional extrusion to 0 ~30with ED direction.Meanwhile,the texture strength increased slightly.(5)The mechanical properties of AZ31 magnesium alloy have been improved after two-pass continuous welding and extrusion.The main reason is that the effect of fine grain strengthening exceeds that of texture softening.At the same time,the rotation of {0001} base plane reduces the difficulty of starting the sliding system on the base plane and further improves the elongation of the material.The increase of yield strength and elongation results in the increase of tensile strength.