Friction stir welding (FSW) technique was preliminary developed to join various low strength and high strength alloys by considering different inputs and known to surpass the flaws which occur in conventional welding processes. The present study is focused on the FSWed interlock lap joint of AA7475-T7 using three-level three factor (33) full factorial design methodology to study the correlation among process parameters with the lap shear strength and hardness. To compare the strength and hardness of interlock lap joint, a typical lap joint has been made with an optimized input parameter obtained from the FSW interlock lap joint. Microstructure analysis, hardness and tensile strength of FSWed interlock lap joints and typical lap joints were done to analyze the robustness of the welds made. Results proved that the strength of FSWed interlock lap joints is high compared to typical lap weld with a ultimate tensile strength of 172.88 N and hardness of 200 HV when the process parameter level is at tool rotation speed of 1400 r/min, welding speed 30 mm/s plunge speed rate 0.06 mm/s. At the tool rotation speed of 1400 r/min dynamic recrystallization of the material occurs which thereby leads to the formation of fine grains in the SZ of the weld metal. © IMechE 2021.