In this study, an investigation was conducted on friction stir spot-welded AA7075
aluminum alloy with mild steel. Fusion welding of these two materials presents
challenges because of differences in melting points and metallurgical
incompatibility. To overcome these challenges, friction stir spot welding was
employed for joining these materials. Trial runs were conducted based on a
central composite rotatable design matrix, which encompassed four factors at
five levels: tool rotational speed, plunge rate, dwell time, and tool diameter
ratio. Shear tests were conducted to evaluate the joint strength, and
subsequently, an empirical equation was developed via analysis of variance.
Notably, a joint fabricated under specific conditions demonstrated exceptional
strength, with the highest fracture load of 9.56 kN. These optimal parameters
included the tool rotational speed, plunge ratio, dwell time and diameter ratio
of 1000 rpm, 4 mm/min, 5 sec and 3.0. This achievement underscores the critical
role of meticulous parameter optimization in achieving superior weld quality and
mechanical properties in dissimilar material joints.