Acoustic effect on the tensile properties and metallurgical structures of dissimilar friction stir welding joints of Al/Mg alloys

Abstract

Abstract The joint strength of friction stir welded Al/Mg alloys is a critical factor for the wide applications of dissimilar joints. In this study, dissimilar Al/Mg alloys joints were made by friction stir welding (FSW) and its variant, ultrasonic vibration enhanced FSW (UVeFSW), respectively. The tensile strength, fracture toughness and fracture location of the whole joints and three (upper, middle, lower) parts of the joints were compared by characterizing the macro-, mesoscopic- and micro-structures of the welds. The influence of ultrasonic vibration on the tensile properties of the joints was discussed. The results showed that the lower part of the welds was the weakest part due to the poor materials mixing/interlocking and a large amount of intermetallic compounds, while the upper part of the weld had the best strength. Good material mixing/mechanical interlocking in the welds was the basis for obtaining higher joint strength, and the thinner intermetallic compound layer was the key to the better toughness of the joint. The application of ultrasonic vibration can improve the tensile strength of each part of the welds, but the improvement rate of tensile strength is greater for the middle and lower parts of the welds.