Laser Welding of Magnesium Alloy

Abstract

The AZ31 magnesium alloy sheet of a 10mm thickness was welded by a CO2 laser welding. The OM, SEM and XRD were used to analyze macroscopic morphology, microstructure, element distribution and phases of the seam. It was found that the topside of the weld sunk, but a good appearance was obtained on the opposite. The fine equiaxed grain was found in the weld which is composed of Mg but no Al-Mg low melting phase. The mean tensile strengths can reach 212MPa values, but a lot of pores existed in the fracture. Magnesium alloy has been widely applied in various fields because of its own advantages[1], such as low density, high specific strength, good recyclability, non-polluting, resource-rich, etc. With the large number of applications of magnesium alloys, it has remarkable industrial significance that the various processing technologies of magnesium alloy were investigated and developed. As is known to all, welding is an important mean of forming structure, thus research on weldability of magnesium alloy material has important theoretical and practical significance. Because magnesium alloy is easily oxidized, it’s prone to burn during welding. Besides, welding crack and coarse grains are likely to appear in the weld due to the higher coefficient of linear expansion and thermal conductivity. These problems will be more serious with the increase of thickness of sheet, so it is difficult to obtain a desirable welded joint. In recent years, research on magnesium alloy welding is mainly involved in TIG welding, electron beam welding, laser welding, friction welding, laser-TIG welding[2-5], etc. Laser welding of the thin plates use the heat transfer characteristics of laser, then the base materials are melted and joined. However, laser welding of the thick plates are use of the deep penetration characteristics of laser, and the high depth-to-width ratio weld in which a lot of pores existed due to evaporation of the metal will be obtained. So far, there are fewer studies on laser welding of the thick plates. In this article, the CO2 laser penetration welding of the AZ31 magnesium alloy sheet with a thickness of 10mm was investigated.