Interlayer growth and fracture at joint interface of pure aluminium/pure nickel friction welding joint

It was clarified how friction welding condition and interlayers composing with intermetallic compound phases affect the joint properties of pure aluminium (Al)/pure nickel (Ni) dissimilar friction welding joint in as-welded and heat treated conditions. The experimental results indicated that all as-welded joints fractured in Al substrate, not joint interface, in spite of friction pressure and friction time. After post-weld heat treatment, the joint tensile strength drastically dropped when the interlayer width increased more than approximately (0.5-2) μm. The maximum number of four interlayers composing with Al ₃Ni, Al ₃Ni ₂, AlNi and AlNi ₃ occurred at joint interface. Al ₃Ni ₂ interlayer grew fastest when the heating temperature exceeded more than 673 K, and its calculated free energy was lowest in those of four interlayers. The fracture occurred at the interface between Al substrate and interlayers regardless of heating temperature. While the surfaces remained typical ductile fractured pattern for the joint heated up to 598 K, they revealed brittle like facet of the joint heated more than 673 K. Detail calculated residual stresses at the periphery of the joint interface of Al substrate were (93-127) MPa in tension.