热挤压形变对AZ31B镁合金TIG焊缝组织及断口形貌的影响

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

以AZ31B镁合金板用同质成分焊丝填充进行TIG对接焊,采用专门设计制作的陶瓷电加热装置在高温拉伸试验机上对接头进行热挤压形变初步试验.结果表明,焊接接头经350℃热挤压形变,可使原焊缝铸态枝晶组织转变为细球状组织,枝晶偏析得到明显改善;同时还可促使原组织中沿α-Mg基体晶界网状分布的β-Mg17Al12相转化成晶内呈弥散分布的二次析出相;通过细化焊缝晶粒、消除脆性β-Mg17Al12相对晶界的弱化作用,在晶内产生弥散强化效应,可使接头的抗拉强度达到母材金属的90%左右,塑性也在一定程度上得到改善.

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.