Protection of the AZ31 magnesium alloy with cerium modified silane coatings

This research investigates the effect of cerium ion addition on the efficiency of a 3-mercapto-propyl-trimethoxysilane (PropS-SH) coating formed on AZ31 magnesium alloy. The coating was obtained by dipping AZ31 coupons in a hydroalcoholic 3-mercapto-propyl-trimethoxysilane solution, added with cerium nitrate, in order to obtain a 5 × 10−3 or 5 × 10−4 M Ce+3 ion concentration. The silane baths were regulated at pH 4 and utilized for filming treatment after 48 h following their preparation. The treated specimens were finally cured for 1 h at 100 °C.The protective efficiency of cerium modified and unmodified PropS-SH coatings was evaluated by recording potentiodynamic polarization curves and electrochemical impedance spectra in a 0.1 M NaCl environment.In comparison to PropS-SH coating, cerium nitrate modified silane layer exhibited noticeably improved performances, in particular in presence of a 5 × 10−3 M Ce3+ concentration. The increased protectiveness and stability of the modified coatings were attributed to a lower porosity and defectiveness and to self-healing ability provided by Ce3+ ion presence.

► Silane conversion coatings as possible alternative to Cr(VI) based pre-treatments.
► 3-mercapto-propyl-trimethoxysilane (PropS-SH) tested on Mg alloys.
► PropS-SH forms a porous conversion coating which allows a rapid electrolyte uptake.
► Ce(NO3)3 addition to pre-treatment bath improves PropS-SH coating performance.
► Ce3+ ions presence provides self-healing feature to the coating.