Influence of secondary welding on microstructure and mechanical properties of friction stir welded joints of AA6061 and AZ31B alloys

Abstract

Butt joints made of 6061-T6 Al and AZ31B Mg dissimilar materials were fabricated using friction stir welding (FSW). Three welding techniques were used in the experimental process: method 1-Mg on the advancing side (AS), method 2-(Al on the AS), and method 3-(Mg was placed on the AS for the first welding experiment, and then the plate was rotated horizontally by 180° so that Al was placed on the AS for the second welding). Focus on the comparative analysis of the second welding and primary welding on the microstructure and mechanical properties of the joint. The results show that the joints with the secondary welding method have the characteristics of onion rings in the stirred zone (SZ), where there is a serious mixture of Al and Mg, and the degree of mechanical bonding is significantly increased. At the same time, the enhanced mechanical effect of secondary welding on the weld led to a change in the microhardness of the SZ. In the tensile tests, the strength of the secondary welded joint was increased to 120 MPa compared to the primary welded joint strength of 89 and 95 MPa due to the increase in the degree of mechanical bonding of the secondary welded joints and the increase in the level of mixing of plastic materials in the SZ. In addition, the type of fracture of the joint in all three welding methods is a brittle fracture.