Fretting wear behaviour of ceramic coating prepared by micro-arc oxidation on Al-Si alloy

Ceramic coating was prepared on Al-Si alloy by micro-arc oxidation (MAO) method. The fretting wear tests of the micro-arc oxidation coating and its substrate alloy have been carried out under normal load of 50 N and displacement amplitudes varied from 2 to 40 μm. Dynamic analyses in combination with microscopic examinations have been performed in detail through laser confocual scanning microscopy (LCSM) and scanning electric microscopy (SEM). The experimental results showed that the MAO coating could shift the mixed fretting regime and slip regime of the substrate alloy to the smaller displacement in Running Condition Fretting Map. Due to the coarse and porous surface structure, the friction coefficient of the MAO coating was higher than that of the substrate alloy in initial stage. With the increase of the number of cycles, the coarse and porous surface was ground to a smooth surface in mixed fretting regime and slip regime, and the friction coefficients in steady stage were reduced to a lower level than that of the substrate alloy. The damage of the coating in partial slip regime was very slight, and it could remain the porous structure even after 10⁴ cycles. The observations indicated that the delamination was the main wear mechanism for the coating in mixed fretting regime. The damage mechanism of the coating in slip regime was identified as the combination of delamination and abrasive wear. Therefore, the MAO coating exhibited widely potential applications for alleviating fretting wear.