Enhancing Al-Si-Cu friction-surfaced coatings via fast rotational rolling process

This study explores the enhancement of Al–Si–Cu coatings via a post-deposition fast rotational rolling (FRR) process applied with one, two, and three passes. Friction surfacing initially refined the Si particles, reducing their average size to 5.1 ± 0.4 µm in the unrolled coating. Subsequent FRR passes further fragmented the Si particles, yielding mean sizes of 4.2 ± 0.3 µm, 3.7 ± 0.5 µm, and 2.5 ± 0.6 µm after the first, second, and third passes, respectively. Microstructural analyses revealed progressive grain refinement with increasing pass number, with surface grain sizes decreasing from 4.2 ± 0.6 µm in the unrolled coating to 2.9 ± 0.2 µm after three passes. Electron microscopy showed that Cu-rich precipitates partially dissolved during the first rolling pass due to deformation-induced heating and reprecipitated with successive passes. Mechanical testing confirmed the benefits of these microstructural changes, with nano-hardness and micro-hardness peaking at 8.6 GPa and 118.5 HV after two passes, followed by a slight reduction after the third pass. Wear measurements reflected similar trends, with the lowest wear rate of 6.3 µg/m recorded after two passes.