Correlation of heterogeneous interface microstructure and mechanical performance of inertia friction welded 6061 Al alloy joint

The non-uniformity of microstructure and property at the interface of the inertia friction welded 6061Al alloy with a grain size of 5 μm was addressed in the present study. The grain became finer from the centre interface region (∼1.1 μm) to the outer interface region (0.8–0.9 μm) due to the enhanced material plastic flow. The textures at different characteristic interfacial regions evolved from different routes: {111}<110> and {001}<110> textures were generated at the centre interface with base metal texture disappeared under the shear effect of friction pressure. Apart from {100}<001> and {210}<001> base metal textures, new textures of {310}<130> and (315)<130> appeared at the outer 1/2R and edge interface regions arising from the rotation of grains. With the enhancements of temperature and material plastic flow, the fraction of precipitates increased from the centre to edge interface, all being higher than that in BM, while the dislocation density showed an opposite trend. The well-predicted microhardness model showed although the Hall–Petch strength mechanism was enhanced from 620 MPa to 650 MPa from centre to edge due to refined grains, the lesser contributions from solid solution and dislocation (390 MPa reduced to 270 MPa) were responsible for the continuously decreased hardness. Microtensile tests also revealed a decreasing trend of local bonding strength from the centre (270 MPa) to the edge interface (230 MPa) with different sizes of dimples observed.