In-vitro biodegradation and corrosion-assisted cracking of a coated magnesium alloy in modified-simulated body fluid

- Ca-P coating improved resistance to corrosion as well as localized corrosion of AZ91D Mg alloy.
- Polarization resistance of the coated alloy was an order of magnitude greater than that of bare alloy.
- Rapid dissolution of the Ca-P coating occurred after immersion in m-SBF solution.
- Coating resulted in improvement of SCC due to suppression of localized corrosion.

A calcium phosphate coating was directly synthesized on AZ91D magnesium (Mg) alloy. Resistance of this coating to corrosion in a modified-simulated body fluid (m-SBF) was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Mechanical properties of the bare and coated alloy were investigated using slow strain rate tensile (SSRT) and fatigue testing in air and m-SBF. Very little is reported in the literature on human-body-fluid-assisted cracking of Mg alloys, viz., resistance to corrosion fatigue (CF) and stress corrosion cracking (SCC). This study has a particular emphasis on the effect of bio-compatible coatings on mechanical and electrochemical degradations of Mg alloys for their applications as implants. The results suggest the coating to improve the general as well as pitting corrosion resistance of the alloy. The coating also provides visible improvement in resistance to SCC, but little improvement in CF resistance. This is explained on the basis of pitting behaviour in the presence and absence of the coating.