The effects of pulse electrodeposition parameters on morphology and formation of dual-layer Si-doped calcium phosphate coating on AZ31 alloy

Controlling the corrosion rate of magnesium alloys in vivo to match the bone repair is crucially important for application as biodegradable orthopedic implants. To solve this challenge, a Si-doped Ca–P coating with a novel dual-layer structure was deposited on AZ31 alloy substrate by pulse electrodeposition. The morphology, composition and formation of dual-layer coating were believed to be determined by pulse electrodeposition parameters, thus the deposition time, temperature, duty cycle, pH value of the electrolyte and the standing duration of mixed electrolyte were regulated to seek possible influences and mechanism on the coating formation. Weight gain and pH monitoring tests were also used to evaluate the performance of coating under the varied parameters. The results indicated that deposition temperature and time remarkably influenced the morphology, homogeneity and crystallinity of Ca–P coating. A uniform and compact coating with better degradation performance was obtained at 60 °C with deposition time of 40 min. The shorter standing duration of the electrolyte lead to an incomplete coating and uneven distribution of Si contents. The two coupled deposition models contributed to this dual-layer structure of Si-doped Ca–P coating and possible formation mechanism was proposed.