Influence of the cathodic activity of magnesium alloys on the electrochemical deposition of calcium phosphate

• Electrochemically coated calcium phosphate on magnesium alloys.
• Cathodic activity of magnesium alloys influenced calcium phosphate coating.
• High coating performance on low cathodic activity of magnesium alloy.

The aim of this study was to investigate whether the cathodic activity of magnesium alloys plays a significant role on the electrochemical deposition of calcium phosphate (CaP). CaP was deposited electrochemically on two magnesium alloys, i.e., magnesium–calcium (Mg–Ca) and magnesium–aluminium–zinc (AZ91), with different electrochemical degradation behaviour. The in vitro degradation behaviour of the CaP coated samples was evaluated using electrochemical impedance spectroscopy (EIS) in simulated body fluid (SBF). The polarisation resistance (RP) of the CaP coated Mg–Ca alloy was ~85% lower than that of the CaP coated AZ91 alloy. Fourier transform infrared (FTIR) analysis showed no difference in the chemical nature of the coatings. However, scanning electron microscopy (SEM) analysis revealed that the coating particles on Mg–Ca alloy were less densely packed than those on the AZ91 alloy. This can be attributed to the higher dissolution rate of Mg–Ca alloy as compared to AZ91 alloy. As a result, the former exhibited higher cathodic charge density which produced higher hydrogen evolution, thereby affecting the coating process.