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Study on the Weld‑Bonding Process Optimization and Mechanical Performance of Aluminum Alloy Joints Mingfeng Li1,2 · Yanjun Wang1 · Zhen Niu3 · Shanglu Yang1,4 Received: 31 March 2020 / Accepted: 29 June 2020 © China Society of Automotive Engineers (China SAE) 2020

Abstract The 5754 aluminum alloy has been widely used in the automotive industry to reduce the weight of vehicles. The weld-bonding (WB) process comprising resistance spot welding and adhesive bonding processes effectively improves the mechanical properties of joints. However, it is still a great challenge in the WB process to obtain high-quality and defect-free nuggets of aluminum alloys. In this study, the parameters of the WB process are optimized and the mechanism of generation of defects during WB is analyzed. The results show that the welding parameters have a significant effect on the nugget sizes, among which the welding current plays the most important role. The residual adhesive can easily cause defects during welding, e.g., expulsion and porosity in the nugget. This can be effectively avoided by optimizing the welding parameters. In addition, the gas in the joints is effectively reduced by adding an appropriate preheating pulse prior to welding, thus lowering the damage degree of the adhesive layer. As a result, welded joints with better weld nugget quality and more stable mechanical properties are obtained. Keywords  Aluminum alloy · Weld bonding · Process optimization · Mechanical performance Abbreviations ANOVA Analysis of variance BIW Body-in-white E/W Electrodes/workpieces RSW Resistance spot welding S/N Signal-to-noise ratio WB Weld bonding

1 Introduction Lightweight vehicles can effectively improve fuel efficiency, conserve energy, and reduce emissions. The use of a lightweight alloy is one of the most effective ways to reduce the * Shanglu Yang [email protected] 1



Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China

2



University of Chinese Academy of Sciences, Beijing 100049, China

3

Beijing Benz Automotive Co., Ltd, Beijing 100049, China

4

Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China



weight of vehicles [1–4]. Aluminum alloys are some of the most favored materials for body-in-white (BIW) production owing to their advantages, such as low density, high specific strength, good processability, and recyclability [5, 6]; these alloys mainly include non-heat-treatable 5 series aluminum alloys (Al–Mg) and heat-treatable 6 series aluminum alloys (Al–Mg–Si) [7], in which the former are commonly used for body structures and internal panels, e.g., 5754 [8], and the latter are used for inner and outer panels, bumpers, etc. [9]. Presently, many processes have been used to join automotive material parts [1, 4, 6, 10], e.g., resistance spot welding (RSW), laser welding, friction stir welding, self-piercing riveting, flow drill screws, and friction stir blind riveting. Of these, RSW is the most im