Effect of Sheet Configuration on Microstructure and Mechanical Behaviors of Dissimilar Al–Mg–Si/Al–Zn–Mg Aluminum Alloys Friction Stir Welding Joints

Friction stir welding (FSW) was used to weld dissimilar Al–Mg–Si/Al–Zn–Mg aluminum alloys in this work. Influences of sheet configuration on microstructure and mechanical properties of the joints were mainly discussed. Results showed that rather different joint cross sections were obtained when using different sheet configurations. Coarser β' phases can be observed at the heat affected zone (HAZ) of the Al–Mg–Si alloy side, which was the main factor affecting the tensile properties and the fatigue properties. Tensile strengths of the dissimilar Al–Mg–Si/Al–Zn–Mg joints using both configurations were higher than that of the Al–Mg–Si FSW joint. When the Al–Zn–Mg alloy was located at the advancing side (AS), the joints owned better fatigue properties due to the bridging effect of the big secondary phase particles.