Electrodeposition of Hydroxyapatite Coating on AZ91D Alloy for Biodegradable Implant Application

The similarity of mechanical properties of Mg and human bones makes Mg and Mg-alloys a potential material for biodegradable implants. However, Mg and Mg alloys corrode too quickly in the tissue fluids, thereby losing mechanical integrity before the tissues have sufficient time to heal. In order to reduce the corrosion rate and enhance the biocompatibility of the (AZ91D), alloy surface was modified with the hydroxyapatite (HAp) coatings. Hydroxyapatite (HAp) coating on AZ91D alloy substrate was prepared by an electrodeposition method and via chemical deposition by an alternative immersion method (AIM). The as-electrodeposited alloy specimen was post-treated with hot alkali solution to convert the electrodeposited calcium hydrogenphosphate coatings into the bone-like hydroxyapatite coatings. The barrier properties of the HAp coatings were studied using the cyclic voltammetry and electrochemical impedance spectroscopy. The protectiveness of the coatings with different treatment times was investigated by a polarization test in a Hanks' solution. The results revealed that hydroxyapatite coating significantly reduced the localized corrosion of the alloy, which is critical for better in-service mechanical integrity. Fourier transform infrared spectroscopy (FTIR) was used to verify the existence of the HAp coating and its morphology on AZ91D alloy surface.