Calcium phosphate (CaPh) coatings are considered promising surface treatments for Mg-based implants. Normally, the phase conversion process of CaPh compounds occurs during immersion in simulated body fluid (SBF) and allows the easy penetration of a corrosive medium. To solve the issue, pre-treatment is often performed, creating an effective barrier that further improves the corrosion resistance of the underlying Mg. In the present work three pre-treatments including hydrothermal treatment, anodization, and plasma electrolytic oxidation (PEO) were performed on pure Mg prior to CaPh deposition. Results indicated that the composition, morphology, and thickness of the CaPh coatings were strongly influenced by the pre-treatments. Dicalcium phosphate dihydrate (DCPD) was formed on PEO surface, whilst DCPD and hydroxyapatite (HA) were deposited on hydrothermally prepared and anodized surfaces. HA could be deposited on the studied samples during immersion in SBF. The electrochemical impedance spectrum indicated that CaPh coating combined with PEO pre-treatment had the highest corrosion resistance at 120 h due to the superior barrier properties conferred by the PEO layer.

Calcium stearate hydrophobic coatings with a hierarchical micro/nanostructure were prepared on 65Mn steel using direct current electrodeposition. The deposition time has a visible influence on the morphology, surface wettability and thickness of the coatings, but little effect on the phase composition. The corrosion behavior of the coated samples in 3.5 wt.% NaCl solution was also investigated. The prepared coatings at different deposition times show different corrosion resistance. The coating fabricated at 30 min has the best corrosion resistance due to the highest water contact angle and thicker coating.