Effect of laser-Ti foil coupling on microstructure and mechanical property of steel/aluminum fusion welding joints

Abstract

The experiment of steel/aluminum laser welding was carried out, numerical simulation of temperature and flow fields inside molten pool was analyzed, and the effect of laser-Ti foil coupling on microstructure and mechanical property of steel/aluminum fusion welding joints was also investigated. With the increase of laser power, the increased penetration width and depth are obtained. The shear force of joint climbs up at first, then declines, and reaches the maximum value when laser power is 1.4 kW, which is improved by 43% compared with that of 1.2 kW. Meanwhile, fracture mode changes from brittle fracture to a mixture of brittle and ductile fractures. In the case of the increased laser power, the improved joint properties are dominated by the metallurgical regulation of Ti foil, which benefits from the accelerated flow of molten pool leading to the Ti element aggregation at the interface and the formation of some new phases. However, when laser power is relatively low, the flow velocity of liquid inside molten pool goes down, and the metallurgical regulation effect of Ti foil is inconspicuous. The property of steel/aluminum joint can be improved by enlarging the steel/aluminum combination area and facilitating Ti foil to generate new phases, but excessive heat input will cause burning loss and induce thermal crack defects, which deteriorates the joint properties.