레이저에 의한 강과 알루미늄 합금의 이종 금속 간 용접에 관한 연구

Abstract

Sung-Min, JOO Advisor: Prof. Han-Sur, BANG, Ph.D

Development of dissimilar weldments represents one of the major challenge and remarkable interests in modern manufacturing processes due to great demands for high quality and high performance. So this thesis work has been focused on lap joints of thin sheet materials and on the investigation of the feasibility of laser welding of dissimilar metallic materials by welding steel to aluminum. Materials used are commercial cold rolled steel sheets (SPCC of 1mm thickness) and aluminum alloys (A1100 and A5052 of both 1mm and 2mm thickness) sheets. One of the major problems in the dissimilar welding is the amount of intermetallic compound layer generated in the fusion zone. The problem not only depends on the relative conductivity of heat and the melting point of the two constituent materials but also in the heat source. Generally, it is known that by using conventional heat source, welding of dissimilar metallic materials is almost impossible due to difficulties to control the amount of heat input, and thus wide fusion zone and intermetallic compounds are generated. To overcome this problem, in this paper, laser beam is used as a welding heat source and this welding offers many advantages over conventional welding processes namely, due to the small spot diameter of laser beams, and high energy densities are reached locally, which finally results in a significant improvement of joining speed and a reduction of the melt pool diameter, and thus small heat input and less intermetallic compounds occurred. Welding conditions have been fixed according to the variation of heat input, keeping all other parameters constant. The Fe (SPCC) sheet with higher melting temperature is positioned on the top of the Al sheet with an overlap of 20mm. Also, multiple laser bead weldings have been made and the bead-to-bead distance is changed to investigate its influence on joint strength. FEM analysis has also been carried out for this model and the mechanical behaviors during dissimilar welding is clarified. When the heat input is controlled appropriately, sound dissimilar weldments are achieved. The result shows the potential of using a laser beam as the leading laser technology for welding of dissimilar materials. Therefore, further investigations have to be carried out in order to utilize all the possible advantages in industrial applications.