The Corrosion Resistance Of CA-P Composite Coating With Surface Pretreatments On AZ31 Magnesium Alloy

At present, the magnesium alloys as biodegradable implant materials attract many researchers’ attention. Since the character of magnesium alloys is too active, it degrades quickly in the physiological environment. It is hoped that the corrosion rate of magnesium alloys can be controlled effectively. On account of this problem,the method of surface modification on the surface of AZ31 was prepared by using substrate-involving pretreatment/Ca-P deposition composite coatings to increase the adheresion between AZ31 substrate and Ca-P coating, at the same time, improving the corrosion resistance of AZ31 magnesium alloys.The pretreatment technology of the pretreatment layer was research systematically. The substrate-involving pretreatment layer has an important impact on corrosion properties of composite coating. It provides the main corrosion resistance for substrate in the composite coatings. Some major factors which effected the corrosion resistance of the coatings was discussed.The main pretreatment technology discussed in the paper was anode oxidation(ANO), micro-arc oxidation(MAO), alkali-heat treatment(ALK-HEAT)and hydrothermal synthesis. The results show that the corrosion resistance of ANO layer is limited. MAO pretreatment can effectively reduces the corrosion current density. ALK-HEAT pretreatment improves the corrosion potential of the substrate.Hydrothermal pretreatment layer acquires the best corrosion resistance because of passivation.When pretreatment layer prepared by hydrothermal method, the factors such as the concentration of the hydrothermal solution, reaction temperature and time affect the pretreatment layer and corrosion resistance of the composite coating. When the reaction temperature is low or the reaction time is short, hydrothermal pretreatment layer is thick., but when the temperature is too high or react for a long time, the pretreatment layer would fall of the substrate. At the same time, the corrosion resistance of the coatings would descend.In the composite coating, the main compositions of Ca-P deposition coatings were HA, DCPD and OCP. HA with cover the surface as the morphology of bonding-like. In the SBF, as the time goes by, the Ca-P coatings can repair the gap in the surface so that the pretreatment layer can maintain its resistance longer.