Comparison of microstructure, mechanical properties, and corrosion behavior of Gas Metal Arc (GMA) and Ultrasonic-wave-assisted GMA (U-GMA) welded joints of Al–Zn–Mg alloy

The microstructural characteristics, mechanical properties, and corrosion behavior were compared for Al–Zn–Mg alloy (thickness: 8 mm) joints obtained via Gas Metal Arc (GMA) and Ultrasonic-wave-assisted GMA (U-GMA) welding. The results reveal that, compared with the GMA welded joint obtained under the same heat input condition, the U-GMA welded joint consists of a larger weld zone (WZ) and narrower heat affected zone (HAZ). The WZ trends of the joints may be summarized as follows: The Fe-rich phases are smaller and considerably fewer in U-GMA welded joint, resulting in higher fracture toughness than that of the GMA welded joint. Ultimate tensile strength (UTS) and elongation determined from tensile testing of the joints are 342 MPa, 7.4 % for U-GMA welded joint and 305.9 MPa, 5.4 % for GMA welded joint. Electrochemical corrosion experiments in a 3.5 wt.% NaCl solution indicate that the corrosion resistance of the WZs in both joints is affected by the distribution of intergranular Fe-rich phases. Each specimen suffered from intergranular corrosion. However, the WZ of the U-GMA welded joint exhibits stronger corrosion resistance than the WZ of the GMA welded joint.