Treatment of Al-Cu-Mg alloy was performed by friction stir spot processing (FSSP). Parametric analysis on the microstructure modification by employing tool rotation speed (ω) and pin dwell-time (t) was performed on several samples processed in air and underwater. It was demonstrated that ω.t could better elucidate the stir zone refinement. Microscopy inspections pointed to the formation of a wide variety in the morphological and size evolution of second-phase particles in the air-treated samples as opposed to uniformly refined spherical particles in the underwater specimens.
