Effect of tool pin geometry and multi-pass intermittent friction stir processing on the surface properties of aerospace grade aluminium 7075 alloy

Multiple pass intermittent friction stir processing was conducted on the surface of an aerospace grade AA7075 alloy using pentagonal and hexagonal profiled pins and its microstructural evolution and mechanical properties were investigated. Results showed a defect-free cross-section with better material mixing for the specimens processed using pentagonal pin. Application of 6 intermittent friction stir processing passes reduced average grain size to 2.32 μm as a result of dynamic recrystallization. Texture index improved after 6 intermittent friction stir processing passes with a higher volume of deformation textures. Microhardness and tensile strength of the alloy increased to 125.5 HV, and 476 ± 10 MPa after 6 intermittent friction stir processing passes due to precipitation strengthening, grain refinement, and dislocation density. Fracture surface investigation revealed an intergranular mode of failure.