Effect of Welding Current on Microstructure and Properties of TIG Welded EW75 Magnesium Alloy

Abstract

Using the wire of the same material as base metal, EW75 magnesium alloy (Mg-7Gd-5Y-1Nd-0.5Zr wt. %) plate with the thickness of 6 mm was welded by TIG to investigate the welding property. Optical microscopy (OM), scanning electron microscopy (SEM) and universal tensile testing machine were used to analyze the appearance of the welding joint, organization performance and mechanical properties.The results revealed that the fusion zone (FZ) was composed of fine equiaxed grains. Precipitated phase distributed on the grain boundary as network structure. The grain size in heat affected zone (HAZ) was coarse because of overheating. The grain size of the FZ increased sharply when the welding current was more than 125A. With the increase of welding current, the grain size of the HAZ remained relatively stable. The hardness curve presented typical “W” shape, and the microhardness of the FZ was the highest, then was the base metal (BM), while the HAZ was the lowest. The welding joint showed uniform scale shape when the welding current was125A.The tensile strength of welding joint was 228 MPa, about 89.4% of the BM, the fracture location was in the FZ and the fracture surface was characterized by mixture fracture.