Characteristics of Joint of Friction-Stir-Welded Aluminum Alloy to Cold-Rolled Steel

Friction-stir-welding (FSW) was performed between high strength aluminum alloy A6061-T6 and cold-rolled steel SPCC-D. The FSWed material was aged again at 453 K for 18 ks to recover hardness of A6061 side in the joint. For the joints of the FSWed material and its aged material, the macroscopic features, microstructures, hardness distributions and element distributions were examined in detail. Especially, the microstructures were investigated through electron back-scattered diffraction (EBSD) for the FSWed material. The result showed that no remarkable defect was formed by FSW and the joint was under good condition. The microstructure of A6061 side in the joint became very fine as well as that of SPCC side near the joint. Such fine microstructures contributed to accelerate diffusion of aluminum and ferrous each other through the interface and to maintain the strength of the joint. Furthermore, no brittle compound layer was detected around the interface. As a result, the static strength of the FSWed material was relatively high. Although the hardness of A6061 side in the joint was decreased by FSW, it was recovered by aging and the static strength of the aged FSWed material reached to that of uniform A6061 material.