Study on the wear resistance and corrosion behaviour of self-sealed MAO/ZrO2 coatings prepared on 7075 aluminium alloy

Self-sealed microarc oxidation (MAO) coatings were prepared on 7075 aluminium alloy by incorporating different concentrations of ZrO2 particles. The wear resistance and corrosion behaviour of MAO- and MAO/ZrO2-coated alloys were investigated. The results show that the tribological behaviour of the coatings was controlled by an abrasive mechanism. The coefficient of friction (COF) for the MAO/ZrO2-coated samples decreased to 0.82, indicating that the wear resistance was significantly improved due to the incorporation of hard ZrO2 particles and the enhanced compactness and surface roughness of the coatings. The sealed pores effectively prevented the permeation of the corrosion solution, thus increasing the electrochemical corrosion resistance. Pores and microcracks would be enlarged and preferentially fractured during slow strain rate testing (SSRT) and thus were the initial sites for corrosion pitting and SCC crack propagation. The interlocking mechanism between the pores (microcracks) and ZrO2 particles enhanced the strength of the pores (microcracks); therefore, the stress corrosion cracking (SCC) susceptibility of the MAO/ZrO2-coated samples was also reduced. Moreover, the MAO/ZrO2 coatings formed with the addition of 4 g/L ZrO2 particles had the best corrosion resistance, and the SCC susceptibility was reduced by 8.1% compared with that of the Al matrix.