Effect of hot extrusion deformation on microstructure and fracture morphology of AZ31B magnesium alloy TIG weld seam

Butt joining of AZ31B magnesium alloy was carried out by tungsten inert gas(TIG) welding process with itself as the filler wire,and a ceramic electric heater was devised for hot extrusion deformation of the resultant joint combining with the high temperature tensile testing machine.The results showed that the casting dendrite in the weld transformed to fine spherical phases after hot extrusion deformation at 350℃,and the dendritic segregation was effectively suppressed.Meanwhile,the original netlike β-Mg₁₇Al₁₂ phases distributing along α-Mg grain boundary transformed to secondary precipitates dispersively distributed within grains.The tensile strength of the joint can reach 90% of the base metal by refining weld metal grain,reducing the weakening of β-Mg₁₇Al₁₂ phases on grain boundaries and producing intragranular dispersion strengthening effect,and the joint ductility can also be improved.