Effect of magnesium content on keyhole-induced porosity formation and distribution in aluminum alloys laser welding

With the aid of transparent glass, the keyhole behavior and porosity formation are directly observed in laser welding of different aluminum alloys. A three-dimensional model is developed to investigate the recoil pressure change. The influences of Mg element on porosity formation and distribution are discussed based on both numerical and experimental results. During laser welding of aluminum alloys, the molten metal in the front keyhole wall is thick. However, with the increasing Mg content, the weld depth increases in the welding direction, and longer time is required to reach the quasi-steady state; besides, the keyhole is more stable, and less keyhole-induced porosity is formed. Based on pressure balance acting on the keyhole wall, the high recoil pressure contributes to the stability of the keyhole, resulting in the suppression of porosity. Higher density of porosity is formed at the middle and bottom of the weld due to the easier collapse of keyhole in the respective regions in laser welding of aluminum alloys with higher Mg content.