Growth characteristics and corrosion resistance of micro-arc oxidation coating on Al–Mg composite plate

Abstract

To investigate the growth characteristics and corrosion resistance of Micro-arc oxidation (MAO) coatings prepared from Al–Mg composite plates under sodium silicate electrolyte, comparative experiments were performed using single plate Al and Mg. The results showed that the breakdown of the Mg plate (P–Mg) in the Al–Mg composite plate occurred first than the Al plate (P–Al). The coating thickness of P–Al and P–Mg gradually converged with time. Because after the Al and Mg plates composite, the increased energy consumption of the P–Al made its discharge more intense and accelerated the growth of its coating, while the situation of the P–Mg was opposite. The SEM observation discovered that the coating defects in P–Al and P–Mg coatings showed a gradually increasing trend as time passed. The corrosion resistance tests showed that MAO could effectively improve the corrosion resistance of the Al–Mg composite plate. Compared with the substrate, the corrosion rate of the P–Al coatings was reduced by more than one order of magnitude, while that of the P–Mg coatings was reduced even more. After soaking in 3.5 wt% NaCl solution for 36 h, the corrosion mass loss of Al–Mg composite plate treated by MAO was reduced by at least two orders of magnitude.