Comparative investigation of tool pin profiles on the microstructure, tribological performance, and electrochemical behavior of AA6063–Cu composites

This study investigates the influence of tool pin geometry on the microstructural evolution, phase transformation, tribological performance, and corrosion behavior of friction stir processed AA6063–Cu metal matrix composites. Surface composites were fabricated using four tool pin profiles, namely cylindrical (CPP), triangular (TPP), square (SPP), and hexagonal (HPP), under identical processing conditions. The microstructures results revealed substantial grain refinement from the AA6063 base metal (74.7 ± 36.2 μm) to 8.6 ± 3.2 μm (CPP), 6.8 ± 2.4 μm (TPP), 5.3 ± 1.7 μm (SPP), and 4.8 ± 1.5 μm (HPP), accompanied by progressively improved Cu particle dispersion. The microstructural analyses also confirmed enhanced precipitate fragmentation, homogeneous Cu redistribution, and increased formation of strengthening Al 2 Cu phases, particularly for the HPP specimen. The tribological performance improved significantly, with the coefficient of friction decreasing from 0.96 ± 0.23 for the base alloy to 0.46 ± 0.06 for the HPP composite, while wear reduced from 3680 ± 356 μm to 2085 ± 185 μm, corresponding to an improvement of approximately 43%. Electrochemical measurements showed remarkable enhancement in corrosion resistance, where the corrosion current density decreased from 3.45 × 10 −4 μA/cm 2 for the base alloy to 1.80 × 10 −5 μA/cm 2 for the SPP specimen, accompanied by a positive shift in corrosion potential from 0.31 ± 0.08 V to 0.52 ± 0.22 V.