이종소재 Al/CFRP 마찰교반접합시 툴 핀 유무에 따른 접합성 평가

Abstract

ABSTRACT

Evaluation of Weldability dissimilar materials Al/CFRP using Friction Stir Welding upon pin existence

Seyoung Lee Advisor : Prof. Bang, Hee-Seon, Ph.D. Department of Welding and Joining Science Engineering, Graduate School of Chosun University

Recently, fuel-efficient, light-weight vehicles emerged as an important issue in the automotive industry as measures of climate change. Especially, in terms of saving energy, the development of technology for welding and bonding of aluminum alloy is intensively invested for energy saving of the car and environmental protection. As international regulation on fuel efficiency continue to be strengthened, weigh reduction of automobile is inevitable. When the weight of the vehicle is reduced by 10%, the fuel consumtion reduced by 3%. acceleration performance increased by 8% and the brake stopping distance is reduced by 5%. Compared with the increase in engine efficiency, light-weight is possible to get higher efficiency at a relatively low cost. This make researches for manufacturing a light vehicle body are actively conducted. On the other hand, although electric vehicles have been continuously studied for the development of future autobobiles, the weight of vehicles has been increasing due to the electric motors and additional batteries. Therefore, high strength steel and some light weigth materials facing a limit of weight reduction. In order to solve this problem, a new joining method is needed to reduce the weight of the car bodies by using aluminum alloys, magnesium alloys, CFRP and other materials such as nonferrous metals and plastics. Proportion of aluminum alloys using as car body is increasing, which were used in make bumpers, hoods and engine blocks. The car body weight can be reduced to 40% by increasing the aluminum ratio applied to the car body. Future automobile development trend is much lighter than ordinary materials and also required non-rigid material. For that, CFRP is suitable as lightweight material. CFRP is 1/4 weight of iron, 10 times stronger, 7 times bigger elastic and has excellent durability, abrasion resistance, heat resistance, impact resistance, and corrosion resistance. But CFRP has low elongation and fracture strength make application of CFRP in automotive industry difficult. In this case, friction stir welding(FSW), one of the solid-state welding methods was invented at TWI(The Welding Institute), Cambridge, involves the joining of metals without fusion materials or filler materials; in other flank, it joins materials by using friction heat. Therefore, in this study intends to apply friction stir welding as a bonding technique for dissimilar material(Al alloy – CFRP). In this experiment, FSW is applied as joining 1.0 mm thickness aluminum alloy(Al5052) to 1.5 mm thickness of CFRP(PA6), which are applied to the automotive industry to evaluate joint characteristics and joining properies according to joining conditions such as tool shape, tool rotational speed, travel speed, plunge depth and surface roughness on the aluminum plate. The mechanical properties and the metallurgical properties of the joints were investigated and analyzed

The results show that the tensile-shear strength with aluminum plate roughness of 3.0 Ra shows the highest strength was 2.0 kN. During the observation by SEM-EDS, joint interface comparison according to the presence of surface roughness, in case of specimens without roughness, it was observed that there was a gap in the joint interface. But in the case of specimens with surface roughness, the bonding was observed better joint condition compare to smooth surface specimen.