Study on the grain morphology and fracture performance of T-joints for Ti6Al4V alloy manufactured by dual laser beam bilateral synchronous welding

Abstract

Titanium alloys have become attractive candidates for structural materials in aviation industry, benefited from their reliable mechanical properties. In the present investigation, dual laser beam bilateral synchronous welding experiments of Ti6Al4V alloy under various welding speeds were performed using optic fiber laser. Experimental results indicate that the heat affect zone has become the weakest region of the joints theoretically. Inappropriate welding speed lead to a severe coarsening of the equiaxed grains below the lower fusion zone, which is the main reason why the tensile strength of the construction decreased significantly. Additionally, the ultimate tensile strength of the T-joint under the welding speed of 22 mm/s has reached 808 MPa, exceeding 90% of the strength of the base metal. According to the fractographs, the T-joints adopted higher welding speeds have failed in the form of microporous aggregation fracture. In contrast to the others, it can be concluded that the fracture mode of the T-joint under the lowest welding speed is a mixed fracture composed of cleavage fracture and ductile fracture.