Fabrication and characterization of hydrophobic microarc oxidation/poly-lactic acid duplex coating on biodegradable Mg-Ca alloy for corrosion protection

A double layer coating was prepared on biodegradable Mg-Ca alloy by microarc oxidation (MAO) followed by dip coating process. The results showed that hydrophobic poly-lactic acid (PLA) as a top layer with thickness of 37-40 μm provides significantly higher corrosion resistance in terms of corrosion current and charge transfer resistance, while the MAO coating alone (8-10 μm) exhibits lower corrosion resistance. However, both coating scenarios demonstrate better corrosion resistance compared with the uncoated Mg- 1.34wt% Ca alloy. Contact angle (CA) measurements showed that the double layer MAO/PLA coated sample presented hydrophobic properties with a CA of 95.30° which is higher than that of MAO coating (CA = 22.90°). The results also exhibit that hydrophobic PLA is effectively seals the porosities of the MAO layer providing effective protection for the biodegradable Mg alloy in the simulated body fluid (SBF) environment and improving the corrosion protection capacity of the MAO surface treatment.