Dissimilar Joining of Low-Carbon Steel to 6061-T6 Aluminum Alloy by Novel Method of Pinless Friction Stir Spot Welding-Brazing

다국어 초록 (Multilingual Abstract)

In this research, AA6061-T6 aluminum alloy sheets were successfully lap-joined to St14 low-carbon steel sheets through thefriction stir spot welding-brazing method with a pinless tool in the presence of a zinc interlayer. The effects of rotating speedand dwell time on the metallurgical structure and mechanical properties were investigated. It was observed that placing thepinless tool on the steel side melts the zinc interlayer and aluminum base metal and leads to forming different microstructureson both sides of the joint. The achievements demonstrated that the joints had a sound shape, and the maximum tensile-shearfailure load (TSFL) obtained for all the joints was more than 4.2 kN. The specimen produced at the rotating speed of 1200 rpmand dwell time of 15 s represented a maximum TSFL and fracture energy of 7.4 kN and 35 J, respectively. Moreover, increasingthe intermetallic layer thickness to almost 25 μm improved the TSFL. However, any further thickness growth caused anintense drop in the TSFL. The intermetallic layer, composed of brittle FeAl3and Fe2Al5phases, was formed near the Al-Znalloy interface with a great amount of Al, and this culminated in an expansion of the joint surface. Furthermore, fracturesurface analysis indicated the occurrence of a fracture at the interface. Some porosities with an average diameter of 50 to255 μm were observed for the sample having the maximum heat input at the fracture surface of the aluminum side, whichwas probably due to the zinc volatilization causing a decrease in the mechanical properties.