Fabrication and Corrosion Resistance Evaluation of Novel Epoxy/Oxide Layer (MgO) Coating on Mg Alloy

A protective novel (MgO) oxide layer (with 91.92% corrosion protection efficiency) was successfully applied on Mg–0.4%Ca alloy using protective oxidation at 390°C (without any pre-treatment). Oxide layer coated Mg alloy was then coated with pure epoxy coating (as top coat). This oxide inner barrier layer protected Mg substrate from 3.5wt % NaCl solution when it passes through from epoxy top layer. Lowest anodic current density and highest charge transfer resistance (1118.124 kΩ cm2) and impedance modulus (│Z│) at low frequency substantiated that the existence of thick epoxy top layer which is integrated (via physical anchoring) with the oxide inner barrier layer could considerably reduce the corrosion rate of magnesium substrate in the chloride containing solutions. Moreover, corrosion mechanism for coated Mg–0.4%Ca alloys was then suggested.