Progress on the control of intermetallic compounds in aluminum/steel friction stir welding

The reliable joining of aluminum/steel dissimilar metals is an important way to realize lightweight and energy-saving design in the automobile industry. Solid-state welding for dissimilar aluminum/steel was more applicable due to their great differences in thermal physical and chemical properties. Friction stir welding (FSW) has great advantages and potentials in joining aluminum/steel dissimilar metals because of its low heat input, short holding time at elevated temperature and low welding distortion. One of the core technologies for high-quality aluminum/steel dissimilar FSW joints could be attributed to the control of intermetallic compounds. Based on the solid-state joining mechanism of aluminum/steel during FSW, the current progress on the regulation of interfacial intermetallic compounds was reviewed from the aspects of welding parameters (including welding speed, rotational velocity, tool offset, tilting angle and plunging depth), tool structures (pin profile, thread and taper angle) and interlayer design (Al and Zn, etc.). Based on the enhancement of joint bearing capacity, new techniques about the FSW of aluminum/steel were summarized, such as keyhole refilling, self-riveting and external assisted FSW. Furthermore, the development trends on FSW of aluminum/steel were prospected.