In-situ defect repairing in hydroxyapatite/phytic acid hybrid coatings on AZ31 magnesium alloy by hydrothermal treatment

• Crack-free hybrid coatings were fabricated on AZ31 magnesium alloy.
• Hydrothermal treatment repaired the defects in the precursor coating.
• Increasing temperature promoted the crystallization of HA.
• Hybrid coatings showed good corrosion resistance.

To improve the corrosion resistance of AZ31 magnesium alloy, a crack-free hydroxyapatite/phytic acid (HA/PA) hybrid coating was synthesized on AZ31 substrate via a chemical conversion deposition to form precursor coating, and followed by a hydrothermal treatment in the saturated CaO solution. During the hydrothermal treatment, the phosphate and calcium ions diffused to the interface of the precursor coating/solution to form amorphous CaP compound and subsequently crystallized into HA particles that repaired the defects in the precursor coating and exhibited a high bonding strength of 24.3 ± 1.7 MPa between the hybrid coating and the magnesium alloy substrate. Electrochemical measurements in simulated body fluid (SBF) revealed that the HA/PA hybrid coating could effectively provide protection for magnesium (Mg) alloy on account of the stable barrier properties.

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