Friction stir spot welding (FSSW) process of 5XXX aluminum alloy has been characterized by comparing histories of Z-axis force and acoustic emission (AE) amplitude during the process. The experiment result shows that both of Z-axis force and AE amplitude vary significantly during the FSSW process. The experiment result also suggests that the change of the AE signal is more pronounced than that of the Z-axis force for the interface between the top and bottom plates and the contact of the tool shoulder. It is suggested that the AE signal can be used as a useful parameter to monitor the FSSW process in addition to the commonly used monitoring parameters for FSSW.
For aluminum alloys, the problems of distortion and hot cracking are inherent with conventional fusion welding processes (Gean, Westgate, Kucza and Ehrstrom, 1999; Khan, Kuntz, Su, Gerlich, North and Zhou, 2007). Friction stir spot welding (FSSW) is a solid-state joining process (Sakano, Murakami, Yamashita, Hyoe, Fujimoto, Inuzuka, Nagao and Kashiki, 2001; Iwashita, 2003), which is derived from friction stir welding (FSW), and has demonstrated a significant effectiveness in joining various difficult-to-weld alloys including aluminum alloys. Therefore, it is natural that FSSW has received an increasing interest from automotive industries which are under significant demands of lightweight components (Hancock, 2004; Dawes and Thomas, 1996). FSSW can be effectively used in the assembly of various automotive components (Lathabai, Painter, Cantin and Tyagi, 2006), such as chassis, crush horns, body enclosures, hoods, and gas tanks. Also, in comparison with other conventional welding processes, FSSW seems to be a safer and more economical joining method. Common advantages of FSSW over conventional welding processes in the joining of aluminum alloys may include excellent mechanical properties, less contamination, less distortion, and low residual stress.
