Effect of Sleeve Plunge Depth on Microstructure and Mechanical Properties of Refill Friction Stir Spot Welding of 2198 A
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JMEPEG DOI: 10.1007/s11665-017-2929-7
Effect of Sleeve Plunge Depth on Microstructure and Mechanical Properties of Refill Friction Stir Spot Welding of 2198 Aluminum Alloy Yumei Yue, Yao Shi, Shude Ji, Yue Wang, and Zhengwei Li (Submitted January 17, 2017; in revised form May 17, 2017) Refill friction stir spot welding (RFSSW) is a new spot welding technology, by which spot joint without keyhole can be obtained. In this work, RFSSW was used to join 2-mm-thick 2198-T8 aluminum alloy sheets and effects of the sleeve plunge depth on microstructure and lap shear properties of the joints were mainly discussed. Results showed that when using small plunge depths of 2.4 and 2.6 mm, joints showed good formation and no defects were observed. Incomplete refilling defect was observed with increasing plunge depth due to material loss during welding. Size of the grains at sleeve-affected zone (SAZ) is smaller than that at the pin-affected zone, and the size becomes bigger with increasing the plunge depth. More secondary phase particles can be observed at SAZ with increasing the sleeve plunge depth. The lap shear failure load firstly increased and then decreased with increasing the sleeve plunge depth. The maximum failure load of 9819 N was attained with plug fracture mode when using 2.6 mm. Fracture morphologies show ductile fracture mode. Keywords
defects, lap shear failure load, microstructure, refilling friction stir spot welding, sleeve plunge depth
1. Introduction Refill friction stir spot welding (RFSSW) is a new variant of friction stir spot welding (FSSW) process (Ref 1). The most outstanding advantage of RFSSW process is that it can join materials without leaving keyholes, which always appear at traditional FSSW joint center and can induce serious stress concentration when FSSW joint bears external forces (Ref 2). Similar to traditional FSSW joint, RFSSW joints also own advantages of smaller distortion, less defect, longer fatigue lives and lower costs since the RFSSW is also a solid-state welding method (Ref 3). Since its invention, the RFSSW process is considered as a promising way to replace traditional spot joining technologies such as riveting and resistance spot welding method (Ref 4, 5). During traditional FSSW process, the plastic material which is squeezed out by the rotating tool stays at the joint edge, forming flash. After tool retreating, no extra procedures are adopted. The flash cannot be refilled into joint, and therefore, a keyhole is left in joint center at the end of welding process (Ref 6). However, during RFSSW process, the tool system is more complicated than that of the traditional FSSW process. It consists of a pin, a sleeve and a clamping ring. The three components were controlled by three independent actuators Yumei Yue, Yao Shi, Shude Ji, and Yue Wang, Faculty of Aerospace Engineering, Shenyang Aerospace University, Shenyang 110136, PeopleÕs Republic of China; and Zhengwei Li, State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China. Contact e-mails:
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