Enhanced corrosion resistance of HA/CaTiO₃/TiO₂/PLA coated AZ31 alloy

In order to reduce the corrosion rate of AZ31 alloy, Hydroxyapatite/calcium titanate/titanium dioxide/polylactic acid (HA/CaTiO₃/TiO₂/PLA) coating which aligned the advances of organic and inorganic coatings was successfully coated onto AZ31 alloy. To overcome the weak adhesion between HA and PLA layers, TiO₂ interlayer was used as a transition layer to increase the adhesion strength of HA/PLA. By the way, CaTiO₃ was formed on the interface of HA/TiO₂ by the reaction of HA and TiO₂ in the anneal process of TiO₂. The inner HA layer was prepared by electro-deposition method subsequently with alkali-heat treatment, and the intermediate TiO₂ layer as well as outermost PLA layer was prepared by dip-coating method. The surface characterization of samples was studied by Scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). And the analysis results manifested that a compact and uniform HA/CaTiO₃/TiO₂/PLA coating was obtained on AZ31 alloy. Immersion corrosion tests and electrochemical tests in Hank's solution at 37 °C were also conducted to study the corrosion behavior of AZ31 alloy, and the results indicated that HA/CaTiO₃/TiO₂/PLA coated AZ31 alloy exhibited superior corrosion resistance compared with that of HA /PLA coated sample. The adhesion mechanism of TiO₂ interlayer and the degradation mechanism of coatings were discussed in this study.