Abstract:The effects of welding current on the macro-morphology, microstructure and mechanical properties of tungsten inert gas (TIG) welded AZ31 magnesium alloy joints with TiO₂ coating were investigated. The results showed that the increase of welding current led to the increase in the depth/width ratio and deteriorated the surface appearance of the welded seams with TiO₂ coating. The grain size of α-Mg and the amount of granular β-Mg₁₇Al₁₂ particles in the welded seams also increased. The welded joints with TiO₂ coating exhibited a deeper weld penetration and larger grain size compared with the welded joint without TiO₂ coating. When the welding current was less than 130 A, the ultimate tensile strength of the welded joints with TiO₂ coating increased with the increase in welding current and then decreased when the welding current was greater than 130 A. The average microhardness of the heat-affected zone and fusion zone decreased gradually with the increase of welding current.

Key words: AZ31 magnesium alloy; A-TIG welding; welding current; TiO₂ coating