Effect of process parameters on the microstructure of resistance spot welding joint of TC4 titanium alloy wear-resistant plate
Titanium alloy wear-resistant plate has a series of advantages such as high stiffness, strength, good corrosion resistance, heat resistance, etc., and has been widely used in aerospace, petrochemical, shipbuilding and other fields. However, due to the high melting point, large heat capacity and poor thermal conductivity of titanium alloy wear-resistant plate, the weld microstructure and grain are easy to coarsene and grow, resulting in reduced plasticity and fracture toughness, which is difficult to ensure the welding quality, limiting its application. The resistance spot welding is not limited by the protective atmosphere, purity and effect, and can overcome the weaknesses that can not be overcome by welding methods such as fusion welding and diffusion welding. In this paper, the microstructure, microhardness and mechanical properties of titanium alloy wear-resistant plate spot welding joint are studied to establish the good performance of the joint spot welding specifications.
The test material was TC4 titanium alloy wear-resistant plate, and the equipment was resistance spot welding machine DN-25. In this work, welding time, specimen thickness and welding current are considered as three influencing factors. After the sample is sanded to remove the oxide layer and cleaned with acetone, spot welding is carried out according to the above three influencing factors. Metallographic samples were prepared after welding.
The microstructure of the resistance spot welding zone of TC4 titanium alloy wear-resistant plate is large needle-like α '. The microstructure of the heat-affected zone near the weld is fine acicular α 'phase, and the growth direction is relatively scattered, forming a net basket structure composed of fine acicular martensite interwoven. The microstructure of the heat-affected zone of the far weld is α+β+ acicular α ', and the newly generated α 'is mutually zonal and cross-layered with the residual α+β. The base material is composed of equiaxed α grains and lamellar α+β biphase structure. With the increase of the distance from the weld center, the microhardness value of the solder joint increases first, reaches the maximum value near the fusion line, and then gradually decreases. The hardness value reaches the lowest value in the heat-affected zone of the far weld, increases again at the base metal, and finally reaches a stable state. For the titanium alloy wear-resistant plate specimen formed by resistance spot welding, as far as the shear resistance index is concerned, when the thickness of TC4 titanium alloy wear-resistant plate is 1mm, the welding current is 6kA, and the welding time is 0.16s, the shear force reaches the maximum.
