Tailoring Weldability for Microstructures in Laser-Welded Near-α Titanium Alloy: Insights on Mechanical Properties

Abstract

With the development of lightweight aerospace structures, the use of the high-quality and efficient laser welding of near-α titanium alloys has received widespread attention and favor thanks to its superior comprehensive performance. The welding experiment of 3 mm thick TA15 titanium alloy was carried out by YAG laser welding, and the material weldability, microstructure, microhardness, and mechanical properties of welded joints were systematically studied. The results indicated that laser welding of TA15 titanium alloy can produce well-formed welded joints without defects such as cracks and porosity. The welded metal used was a typical basket-weave microstructure composed of a large number of α′ martensitic phases and a small number of high-temperature residual β phases, and the heat-affected zone was a staggered arrangement of undissolved α phase and needle-like α′ martensite. The microhardness of the welded joint showed a hump distribution, and the hardness of WM fluctuated between 410 and 450 HV since the martensitic transformation occurred during the solidification of the weld under thermal cycling, and the β phase changed to the needle-like α′ phase. The tensile test indicated that the fracture position was located in the base metal area, and the fracture morphology showed the equiaxial dimple morphology of different sizes in a ductile fracture mode. The welded metal had the lowest impact performance (average value of 5.3 J) because the weld area was predominantly coarse α′ martensite. This experiment conducted systematic, in-depth, and extensive research on welding processes, hardness, tensile, impact, and fracture mechanisms. Based on the special product applications in the aerospace field, it was more targeted and conducive to promoting the application of the welding process in this material.