Effect of Shielding Gas and Laser Wavelength in Laser Welding of Magnesium Alloy Sheet

Abstract

Utilization of magnesium alloy has increased in recent years as structural metals, such as automotive industry and mobile information tools. Hence welding techniques are required to be developed for these applications. Lasers are known to be an excellent tool for them. This paper presents the laser weldability of wrought type of AZ31 magnesium alloy with high power continuous wave (cw) Nd: YAG and CO₂ lasers. The effects of center and back shielding conditions were examined. In the case of CO₂ laser welding without back shielding, backside of the bead formed groove resulted from the reaction of the laser-induced plasma and low surface tension of the magnesium. In the case of Nd: YAG laser without back shielding, a welded bead was significantly better than that with CO₂ laser. Because the metal vapor did not change to plasma plume due to the short wave length, it played the role of shielding the backside of the bead. From the tensile tests of the butt joints fabricated with CO₂ and Nd: YAG laser, tensile strength of the joints which were made with Nd: YAG laser in both case with and without back shielding was sufficiently high.