Abstract: Mg/Al dissimilar alloys are successfully joined by gas tungsten arc welding using ER5183、ER5356 welding wire. Microstructure characteristics of the Mg/Al welded joint are analyzed by means of optical microscope and scanning electron microscope, the distribution of elements is studied by means of electron probe micro-analyzer and energy dispersive spectroscopy, microhardness of two joints are compared and analyzed by micro-sclerometer. No continuous intermetallic compound layer is observed in the joint. Joints with sound surface and free of defects are achieved. Grains of the weld seam using ER5183 wire are finer than that using ER5356 wire. There are much fewer Mg-Al brittle intermetallic compounds in the seam using ER5183 wire. The fusion zone in magnesium side is composed of α-Mg+γ-Al12Mg17 eutectic structure and boundary γ-A112Mg17 precipitations. The weld seam near magnesium is mainly composed of α-Mg+γ-A112Mg17 structure. Contents of Mg and Al elements keep stable in the fusion zone in magnesium side. Content of Mg in the weld seam keeps decreasing while content of Al increasing from the magnesium side to the center of the seam, and both reach to a stable value in the weld seam near aluminum. If the content of Mg in the wire is controlled in a proper value, intermetallic compounds would disperse in the weld seam and weldability of Mg AZ31/Al 7005 dissimilar metals could be improved.

Key words: dissimilar metals, distribution elements, magnesium-aluminum wire, micro-hardness, microstructure