Improvement of Mg/steel dissimilar laser welded joint properties produced by beam oscillation

Abstract

Oscillating laser welding technology was utilized to enhance the joint properties of AZ31B magnesium (Mg) alloy to DP590 dual-phase steel based on the joint structures with adding Ni powder to the prefabricated V-groove. The influence of beam oscillation on laser energy distribution and grain size in molten pool and improvement of joint performance were revealed. At the optimal welding parameters, the tensile-shear property of joint reaches the maximum value of 2.2 kN, which is improved by 69.23% compared with the no-oscillation mode. With the oscillation of laser beam, the heat input into the fusion zone changes, and the uniformity of laser energy distribution is improved. Some defects such as pits, cracks are suppressed, and the width of molten pool is increased. At the same time, the dendrites growing along the edge of molten pool are broken and refined due to the enhanced molten pool stirring effect induced by the rotation of keyhole. Compared with the circular oscillation mode, in the case of line oscillation mode, there is less overlap of the oscillating tracks, which avoids multiple remelting and further refines the grain, hence, the mechanical performance of Mg/steel joint is further improved by beam oscillation.