• PDF / 3,366,761 Bytes
• 12 Pages / 593.972 x 792 pts Page_size
• 74 Downloads / 274 Views

DOWNLOAD

REPORT

---

JMEPEG (2017) 26:5085–5096 DOI: 10.1007/s11665-017-2928-8

Effect of Thread and Rotating Speed on Material Flow Behavior and Mechanical Properties of Friction Stir Lap Welding Joints Shude Ji, Zhengwei Li, Zhenlu Zhou, and Baosheng Wu (Submitted November 25, 2016; in revised form April 16, 2017; published online September 21, 2017) This study focused on the effects of thread on hook and cold lap formation, lap shear property and impact toughness of alclad 2024-T4 friction stir lap welding (FSLW) joints. Except the traditional threaded pin tool (TR-tool), three new tools with different thread locations and orientations were designed. Results showed that thread significantly affected hook, cold lap morphologies and lap shear properties. The tool with tipthreaded pin (T-tool) fabricated joint with flat hook and cold lap, which resulted in shear fracture mode. The tools with bottom-threaded pin (B-tool) eliminated the hook. The tool with reverse-threaded pin (Rtool) widened the stir zone width. When using configuration A, the joints fabricated by the three new tools showed higher failure loads than the joint fabricated by the TR-tool. The joint using the T-tool owned the optimum impact toughness. This study demonstrated the significance of thread during FSLW and provided a reference to optimize tool geometry. Keywords

fracture modes, friction stir lap welding, hook, lap shear failure load, thread

1. Introduction Friction stir welding (FSW) was invented in 1991 by TWI (Ref 1). A rotating tool, composing of a shoulder and a pin, is plunged into the abutting edge of two sheets to be joined. Heat input is firstly produced by the friction between tool and base material (BM). Then, the materials adjacent to tool are heated, softened and mixed. After traveling along the abutting line for a predetermined distance, tool is retracted and joint is formed (Ref 2). The most outstanding superiority of FSW is that materials can be joined at solid state. Hence, FSW is very suitable to join some high strength precipitation hardening materials such as 2XXX and 7XXX aluminum alloys. Since invention, FSW has gained increasing attentions from the researchers (Ref 3-5). Besides butt welding joint, another typical joint of FSW is friction stir lap welding (FSLW) joint. FSLW is achieved by plunging a tool into two overlapping sheets and then moving the tool forwards (Ref 6). Friction stir spot welding (FSSW) shares same principle with FSLW except for travel process. During FSLW or FSSW, a characteristic feature is ‘‘hook’’ (Ref 7, 8). Hook is formed due to the vertical bending of original lap interface. Hook diminishes the integrity of lap joint since crack easily propagates along hook when joint bears external loads (Ref 9, 10). Shude Ji, Zhenlu Zhou, and Baosheng Wu, Faculty of Aerospace Engineering, Shenyang Aerospace University, Shenyang 110136, China; and Zhengwei Li, State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001, China. Contact e-mails: [email protected] and [email protected].

Journal o