Corrosion behaviour of a magnesium matrix composite with a silicate plasma electrolytic oxidation coating

The corrosion behaviour of AZ92 magnesium alloy reinforced with various volume fractions of silicon carbide particles (SiCp) and treated by alternating current (AC) plasma electrolytic oxidation (PEO) was investigated in humid and saline environments. For untreated composites, corrosion attack started around the Al–Mn inclusions and gradually developed into general corrosion without significant galvanic coupling between the matrix and the SiCp. PEO coatings consisted mainly of MgO and Mg2SiO4, and revealed increased hardness, reduced thickness and slightly higher corrosion resistance with increasing proportion of reinforcement. Pit formation and hydration of the outer layer were the main mechanisms of corrosion of PEO-treated specimens.

Research highlights
► The paper addresses the corrosion behaviour of PEO coated magnesium matrix composites in 3.5 wt.% NaCl, salt fog and high humidity environments.
► The results provide further information of reinforcement influence on the morphology of PEO coatings and their corrosion behaviour.
► Electrochemical and gravimetric tests are performed in various media.
► Coating morphology and corrosion products are studied in detail.