Effect of Incomplete Penetration Defects on Mechanical and Fatigue Properties of Friction-Stir-Welded 6802-T6 Joint PDF

j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 5 : 4 0 2 1 e4 0 3 1 Available online at www.sciencedirect.com journal homepage: www.else...

j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 5 : 4 0 2 1 e4 0 3 1 Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/jmrt Original Article Effect of incomplete penetration defects on mechanical and fatigue properties of friction-stir- welded 6802-T6 joint Xianglai Xu a, Qingyong Liu b, Sun Qi c, Hongliang Hou d, Jing Wang a, Xueping Ren a,* a School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing, 100083, China b Chinalco Materials Application Research Institute Co. Ltd., Beijing, 100083, China c School of Materials Science and Engineering, Dalian University of Technology, Dalian, 116024, China d AVIC Manufacturing Technology Institute, Beijing, 100024, China article info abstract Article history: In this study, 6802-T6 alloy plates were welded using tools with different pin lengths. Received 28 June 2021 Different depths of incomplete penetration defects, including kissing bond (K) defect and Accepted 6 October 2021 remain joint surface (R) defect, were obtained. Mechanical fracture and kernel average Available online 12 October 2021 misorientation (KAM) maps indicated that joint root tearing caused K defect during the friction stir welding (FSW) process. The critical value for incomplete penetration geometry Keywords: appeared to be a depth of 0.4 mm. Within this interval, the ultimate tensile strength of the 6802-T6 alloy joint (thickness of 3 mm) was more than 224 MPa, and the fatigue strength exceeded Incomplete penetration 70 MPa at 107 cycles. Friction stir welding © 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). aluminium body products is still in its infancy, and the form 1. Introduction design and quality specifications of the joints are not yet complete. Joints typically have incomplete penetration de- Friction stir welding (FSW) is a new type of solid-phase fects, including K defects and R defects, in the root. welding that has been widely used in the aerospace, ship- Sato [3,4] found that oxide particles appear inside R defects, building, automobile manufacturing, and military industries. which formation is primarily caused by the weak stirring Particularly, in automobile manufacturing, FSW is widely ability of the tool. The oxides are not sufficiently dispersed, used in place of traditional welding technology for rivet con- which results in weak welding. Many scholars have studied nections and to weld aluminium alloys. The advantages of the influence of K defects on the mechanical and fatigue FSW are high-quality and highly efficient linking of properties of joints. Qi et al. investigated the tendency of aluminium products, improved efficiency, and reduced pro- root defect depth to increase with travel speed, which causes cessing costs [1,2]. However, the application of FSW to the joint strength to decrease. However, minor root defects * Corresponding author. E-mail address: [email protected] (X. Ren). https://doi.org/10.1016/j.jmrt.2021.10.028 2238-7854/© 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/). 4022 j o u r n a l o f m a t e r i a l s r e s e a r c h a n d t e c h n o l o g y 2 0 2 1 ; 1 5 : 4 0 2 1 e4 0 3 1 eliminate incomplete penetration defects but also prevent Table 1 e Chemical composition of 6802-T6 alloy (wt.%). thinning of the joint. However, they have stricter re- Si Fe Cu Mn Mg Cr Al quirements in terms of welding control when compared with 1.00 0.24 0.027 0.68 0.72