All-position plasma arc welding process for thick TC4 tube and mechanical properties of welded joints

A new plasma arc welding process for thick-walled TC4 titanium alloy tube was investigated. All-position high-quality welding joints of titanium alloy were achieved through parameters optimization. The microstructure, fracture morphology and microhardness of the welded joints at ordered locations were characterized by optical microscopy, scanning electron microscopy and micro Vickers hardness tester. The results reflected that the microstructure of the weld metal and the heat-affected zone of the characteristic joint were mainly composed of basket-shaped α' phase, needle-like α phase and coarse β phase. The tensile fractures of specimens was occurred at base metal, revealing well tensile properties. The fracture morphology of the impact specimens was ductile fracture. The hardness of weld metal and heat affected zones was higher than that of base metal, respectively.