A composite coating for corrosion protection of AM60B magnesium alloy

摘要

Oxide films have been produced on the AM60B magnesium alloy using micro-arc oxidation process in an environmentally friendly alkaline solution with and without addition of different oxides nanoparticles (TiO-2, ZrO-2 and AI2O3). The influence of these compounds on the corrosion resistance of the anodic oxides produced in oxides nanoparticles containing solutions in comparison with those produced in nanoparticles solution free has been assessed. Because of the oxides porosity inherent in the sparking process organofunctional silanes as top coats have been applied to seal pores and cracks and achieve more protective systems. The surface and cross-section morphology of the samples were analyzed by Scanning Electron Microscopy (SEM). The corrosion resistance of the samples was evaluated in 0.6M NaCI solution at room temperature using potentiodynamic polarization tests. The addition of nanoparticles to the anodizing solutions slightly affects the oxides corrosion resistance in comparison with anodic oxides produced in nanoparticles free solutions. Specimens anodized in ZrO-2 and AI2O3 containing solutions snowed better adhesion (data not reported in this paper) compared to samples anodized in TiO-2 containing solution and for this reason were chosen for silane deposition. Two different silanes were used, namely octyltrimethoxysilane (OSi) and 1, 2-bis[triethoxysilyl] -ethane (BTSE). Cross-section SEM examination of OSi- and BTSE-coated substrates showed that the former covers better the undermining surface and penetrates deeper the cracks originated in the anodization process. The anodizing in oxides nanoparticles rich solutions (ZrO2 or AI2O3) followed by a silane top coat treatment performed using OSi as precursor could be an interesting way to synthesize adherent corrosion resistant coatings on magnesium alloy AM60B in a short process time (11 min).