Oscillating laser welding of AZ31B magnesium alloy to DP590 dual-phase steel

Oscillating laser welding of AZ31B magnesium (Mg) alloy to DP590 dual-phase steel was performed in an overlap Mg-on-steel configuration with Sn foil added to lap joint, numerical simulation of laser energy distribution, temperature and flow fields inside molten pool was analyzed, and the effect of oscillating laser beam on microstructure and mechanical properties of joints were also investigated. A sound Mg/steel dissimilar joint is obtained under the beam rotation of oscillating laser assisted by Sn foil. Some defects, such as spatter and collapse, can be avoided in welding joints. In the case of circular oscillation mode, the shear force of joint reaches the maximum value of 1487 N when oscillation amplitude is 1.5 mm and oscillation frequency is 100 Hz, which is improved by 121.94 % compared with the non-oscillation mode. As laser beam oscillates, the uniformity of laser energy distribution is improved, the energy peak decreases. As a result, the laser action range increases and the joint width increases. In addition, the dendrites on both sides of molten pool are broken due to the increased flow and the enhanced vortex and convective effects induced by the rotation of keyhole. Hence, the performance of Mg/steel joint is improved.