Phosphate coatings on WE43 magnesium alloy with improved corrosion resistance and bonding strength and effects of hydrothermal temperature

Magnesium (Mg) alloys are promising orthopedic biomaterials due to their biocompatibility and degradability, but rapid and uncontrolled corrosion hampers clinical applications. In this study, magnesium potassium phosphate (MKP) coatings are prepared on the WE43 Mg alloy hydrothermally to improve the corrosion resistance and bonding strength. The influence of different conversion temperatures is evaluated. The MKP150 coating prepared at 150 °C is dense and free of cracks. Its corrosion rate (P_i, 0.07 mm·y⁻¹) and hydrogen evolution rate (HER, 7.9 × 10⁻⁴ mL·cm⁻²·h⁻¹) are one order of magnitude lower than those of the bare Mg, and the corrosion current density (i_corr, 2.97 μA·cm⁻²) decreases by 92.8 %. The hydrothermal temperature changes the corrosion resistance because it affects the critical nucleation radius and rate of MKP. The coating prepared at 150 °C has the optimal crystal size, thickness, shrinkage stress, as well as corrosion protection. On the other hand, microcracks are observed from the MKP180 coating deposited for a longer time. As a result of the in situ growth of the phosphate coating, the critical load of MKP150 reaches 7.05 N indicative of better adhesion strength. Coatings with high corrosion resistance and bonding strength on Mg alloys have large potential in clinical applications. 

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