이종재 Al-CFRP의 Pinless툴을 이용한 마찰교반점용접 특성에 관한 연구

Abstract

Today, regulations on automobile emissions and fuel efficiency are increasingly being strengthened to cope with problems such as air pollution and global warming all over the world. Therefore, the automobile industry must satisfy the regulations. Vehicle weight reduction is attracting attention as the most effective way to reduce carbon dioxide emissions by improving fuel efficiency. Recently, the automobile industry has been using ultra-high strength steel plates, hot stamping and hydroforming to reduce the weight of vehicles, but it is difficult to meet the tightening emission regulations. Therefore, it is focused on strengthening the strength of the car body and reducing the weight of the vehicle by replacing it with a lightweight material. Aluminum has an excellent specific strength compared with steel and is excellent in corrosion resistance and recyclability. When replacing BIW (Body In White) entirely with aluminum, up to 45% weight reduction is possible. In addition, carbon fiber reinforced plastic (CFRP), which is attracting attention as a next-generation lightweight material, has 60% weight and 5 times higher strength that that of aluminium.

CFRP is under many restrictions apply to the actual automobile parts because of the disadvantages such as low elongation and breaking strength. In order to solve these problems, Multi-Material Mix Technology that mixes various materials is emerging. By using different properties between materials, it is possible not only to reduce the weight but also to select and arrange materials having suitable mechanical properties to obtain optimized performance and reduced manufacturing cost. However, it is difficult to realize high-strength and high-durability joints by using the conventional bonding technique because the material properties between materials are different from each other. Therefore, it is important to secure appropriate bonding technology in the development of dissimilar materials parts.

In this study, we applied the friction spot joining(FSJ) process as a bonding method for Al/CFRP. For this purpose, the reliability of the joints is secured by evaluating the bonding characteristics and the mechanical and metallurgical characteristics according to the parameters of each process.

In order to investigate the characteristics of Al/CFRP using friction spot joining, plunge depth, the rotation speed, and the dwell time were selected as parameters. The material used in the research is aluminum alloy Al5052 1mm (t), which is lightweight material used in vehicles. As CFRP material, 'LANXESS' 'Tepex dynalite' uses 3k carbon fiber and polyamide 66 thermoplastic resin and thickness is 1.5mm (t). Lap Joints friction stir welding was performed by superimposing the aluminum plate on the upper plate and the CFRP on the lower plate by 80mm (L) X 30mm (W). In addition, a pinless tool was used to apply heat and pressure to the specimen when Al5052 / H32 and CFRP were bonded. Surface roughness was given to the material before all experiments were carried out. During the test, the temperature of the joint surface was measured and tensile – shear test was performed after the experiment. In this study, thermal distribution characteristics of Al/CFRP joints were investigated using numerical analysis program and compared with the experiment.

As a result, maximum tensile – shear strength of 3.65kN was obtained at plunge depth of 0.4mm, rotation speed of 500rpm and dwell time of 15sec. In addition, the reliability of the joint was confirmed by comparing the numerical analysis with the experiment.