4. Welding and Joining

As mentioned in Chap. 2, the Project has been conducting materials development of ultra-high strength steel sheets of medium- and high-carbon steel, aluminum alloys, magnesium alloys, titanium alloys, CFRTP and other materials that will contribute to reduction of the car body weight. At the same time, it has been also developing welding and joining methods for ultra-high strength steel sheets and 3 combinations of dissimilar materials: steel to aluminum alloy, aluminum alloy to CFRTP, and steel to CFRTP. In this chapter, 6 types of joining processes, which are welding, brazing, friction joining, interface-melt joining, adhesive bonding and mechanical fastening, are described for multi-material structure car body consisting of the newly-developed materials and existing materials. The joint strengths of the feasible joining processes developed are mainly focused together with the target values for joining of ultra-high strength steels and dissimilar materials respectively.