A new spot joining technology relying on a consumable joining bit has been developed and evaluated on dual phase (DP) 980 steel and a dissimilar combination of aluminium alloy 5754-O and DP 980. This new process, called friction bit joining (FBJ), uses a consumable bit to create a solid state joint in sheet materials by the action of cutting and frictional bonding. FBJ lap shear fracture loads were 14?7 kN for 1?4 mm DP 980 compared to 16?6 kN for RSW, for the same spot diameters. FBJ of a dissimilar combination of aluminium alloy 5754-O and DP 980 produced joints with average lap shear fracture load of 6?3 kN. This strength is greater than lap shear fracture load obtained by self-piercing riveting (SPR) in HSLA 350 bonded to AA 5754-O.

Spot joining of dissimilar metal alloys is difficult because of differences in melting temperature as well as differences in composition. If a fusion welding process like resistance spot welding is employed, then alloys mix in the fusion zone and can create brittle intermetallic compounds during solidification. When self-piercing riveting (SPR) is used, the alloys to be joined must be ductile enough to be formed around the rivet. In this paper, a new approach to joining dissimilar metal alloys has been studied, where a consumable bit has been used to create a spot joint between dissimilar alloys. The resulting joint has both metallurgical and mechanical bonding characteristics and can be made between very soft and very hard alloys, like dual phase (DP) 590 and DP 980 and light metals like AA 5754. Lap shear strengths of joints made by friction bit joining (FBJ) are similar to or better than comparable joints made by self-piercing riveting.

The authors study a new solid-state spot joining process, friction bit joining (FBJ), which relies on the use of a consumable joining bit. It has been reported that FBJ is feasible for the joining of steel/steel and aluminum/steel, but the metallurgical characteristics of the joint for enhancement of the properties and reliability remain unclear. Therefore, this study produced friction bit joints in DP980 steel and then examined the microstructures in the joint precisely. In this article, the microstructure distribution associated with hardness in the friction-bit-joined DP980 steel and the microstructural evolution during FBJ are reported.

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