Analysis on the Fracture of Al-Cu Dissimilar Materials Friction Stir Welding Lap Joint
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JMEPEG DOI: 10.1007/s11665-017-3029-4
Analysis on the Fracture of Al-Cu Dissimilar Materials Friction Stir Welding Lap Joint Hongyu Sun, Qi Zhou, Jun Zhu, and Yong Peng (Submitted May 22, 2017; in revised form August 30, 2017) Friction stir welding (FWS) is regarded as a more plausible alternative to other welding methods for Al-Cu dissimilar joining. However, the structure of an FSW joint is different from others. In this study, lap joints of 6061 aluminum alloy and commercially pure copper were produced by FSW, and the effects of rotation rate on macromorphology, microstructure and mechanical properties were investigated. In addition, a fracture J integral model was used to analyze the effect of microstructure on the mechanical properties. The results revealed that the macrodefect-free joints were obtained at a feed rate of 150 mm/min and 1100 rpm and that the failure load of the joint reached as high as 4.57 kN and only reached 2.91 kN for the 900 rpm, where tunnel defects were identified. Particle-rich zones composed of Cu particles dispersed in an Al matrix, and ‘‘Flow tracks’’ were observed by the EDS. The J integral results showed that the microdefects on the advancing side cause serious stress concentration compared with the microdefects located on the AlCu interface, resulting in the fracture of the joints. Keywords
Al-Cu lap joint, Fracture J integral, Friction stir welding, Mechanical property, Microstructure
1. Introduction The dissimilar joining of aluminum to copper is increasingly being used in the electrical industry. It is characterized by the ability to maximize the use of different material advantages for industrial production (Ref 1-4). However, due to the different chemical, mechanical and thermal properties of aluminum and copper, there are challenges when joining these materials (Ref 5, 6). In the past, welding methods, including braze welding (BW), electron beam welding (EBW) and fusion welding (FW), have been adopted to join Al and Cu (Ref 7-9). However, limitations exist with these methods to various extents. For example, the joint strength of BW is low, EBW is restricted by the size and shape of the workpiece, and FW produces intermetallics as part of the welding process. Friction stir welding (FSW) is a solid-state welding technique that has unique advantages, such as low distortion, energy efficiency and versatility, when joining dissimilar materials (Ref 10). In the past decade, much attention has been given to the FSW of dissimilar materials. Through the present, dissimilar materials connection, such as Al-Mg (Ref 11), Al-Steel (Ref 12), Al-Ti (Ref 13), Fe-Mg (Ref 14), has been achieved by FSW. In addition, many researchers have been interested in using FSW to join Al-Cu. Jingqiao Zhang et al (Ref 15) conducted underwater FSW experiment and found that the amount of intermetallics can be restrained in this scenario. Kuang et al. (Ref 16) used zinc sheet as a middle layer to decrease the Hongyu Sun, Qi Zhou, and Yong Peng, School Materials Science and Engineering, Nanjing University of
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