The improvement of PEO coatings and the optimization of
their surface aspects are of major importance. In this current work, the influence of dual PEO coating on
strip-cast AZ31 Mg alloy substrate has been evaluated with the aim of improving the surface and
corrosion protection aspects. For this purpose, AZ31 Mg substrates are subjected to single and dual PEO
processing in silicate and phosphate electrolyte under similar condition. Scanning electron microscopy
(SEM) analysis confirmed that the number of pores in PEO coating processed in silicate electrolyte is
higher than others. X-ray diffraction analysis of PEO coatings showed that the surface coating is mainly
comprised of Mg2SiO4, Mg3(PO4)2 and MgO with different quantity based on PEO processing. Compared
with the AZ31 Mg, the corrosion potential (Ecorr) of both type PEO coatings was positively shifted about
250e400 mV and the corrosion current density (icorr) was lowered by 3-4 orders of magnitude as result
of adequate corrosion protection to the Mg alloy in 3.5% NaCl solution. All of the observation obviously
showed that the dual PEO coating provides better corrosion protection performance than their respective
single due to its synergistic beneficial effect.