Corrosion resistance of biodegradable polymeric layer-by-layer coatings on magnesium alloy AZ31

Biocompatible polyelectrolyte multilayers (PEMs) and polysiloxane hybrid coatings were prepared to improve the corrosion resistance of biodegradable Mg alloy AZ31. The PEMs, which contained alternating poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), were first self-assembled on the surface of the AZ31 alloy substrate via electrostatic interactions, designated as (PAH/PSS)(5)/AZ31. Then, the (PAH/PSS)(5)/AZ31 samples were dipped into a methyltrimethoxysilane (MTMS) solution to fabricate the PMTMS films, designated as PMTMS/(PAH/PSS)(5)/AZ31. The surface morphologies, microstructures and chemical compositions of the films were investigated by FE-SEM, FTIR, XRD and XPS. Potentiodynamic polarization, electro-chemical impedance spectroscopy and hydrogen evolution measurements demonstrated that the PMTMS/(PAH/PSS)(5)/AZ31 composite film significantly enhanced the corrosion resistance of the AZ31 alloy in Hank's balanced salt solution (HBSS). The PAH and PSS films effectively improved the deposition of Ca-P compounds including Ca-3(PO4)(2) and hydroxyapatite (HA). Moreover, the corrosion mechanism of the composite coating was discussed. These coatings could be an alternative candidate coating for biodegradable Mg alloys.