Mechanical behavior and fracture of easily-decomposable dissimilar-materials-joint fabricated by friction stir forming

In this paper, the authors discuss dissimilar materials joining structures fabricated by friction-stir forming (FSF) and easily decomposable. Dissimilar-materials-joining has been successfully studied as a key for new producing light-weight parts; however, it can be a barrier to recycling in the future. The authors suggested the concept of easily separable joining of dissimilar materials employing friction-stir forming (FSF). A joined plate having a keyhole was prepared and put into a mold having a hook cavity. An aluminum alloy plate was put on and friction stirring was conducted on its back surface. Due to the massive heat and compression force generated by the friction stirring, a hook-like joint was successfully generated, and the substrate and joined member are sheared to disconnect them by hitting with a plastic hammer; however no room was observed between the hook and joined material after forming. Opposite hooks generated by the above approach join dissimilar materials tightly, but the materials can be separated smoothly after cutting them between the hooks. In the experiment, a pair of a 0.8mm-thick JIS SPCC steel sheets and a 3mm-thick JIS A5083P-O aluminum alloy plate was joined. The authors evaluated the joints by tensile and shear tests and discuss their mechanical behavior and failure. The tensile strength of the joint was 652N (average). In the tensile tests, the deformation of the keyhole of 0.8mm-thick SPCC steel sheet caused the failure of the joint. The shear strength was affected by the shear direction, i.e. 1010N at 0deg, 705N at 45deg, and 1320N at 90deg (average) for the connecting line between hooks. It was thought that the hook-like joints had enough strength for the cross-sectional area of their stems (i.e. 4.16mm2).