Scuffing resistances of Al–Si alloys: effects of etching condition, surface roughness and particle morphology

Scuffing resistances of two eutectic Al–Si alloys with different second phase particle morphologies, were investigated using a block-on-ring wear machine under dry sliding conditions. The sample surfaces were modified by mechanical polishing and chemical etching to create different surface topographies. It was shown that at constant load (5 N) and speed (0.5 m s−1), the sliding distance to scuffing initially increased with etching time as the particles prevented the direct contact between the counterface and aluminum matrix. The onset of scuffing became less sensitive to surface conditions at longer etching times due to the weakening of particle/matrix interfaces. Polishing the surfaces to an optimum roughness (Ra=0.4 μm) prior to etching improved the resistance to scuffing. In the alloy containing second phase particles with small aspect ratios (more equiaxed particles), the onset of scuffing was delayed. Scratch tests showed that two types of fractures occurred in the hard phases during the sliding process: fracture from the root of the particles, and fracture of the edges of the particles. Both contributed to wear and scuffing, but the former process was more detrimental for scuffing of the alloy surfaces.