Effect Of Different Post-treatment On Microstructure And Mechanical Properties Of The Coating On Pure Magnesium By Ultrasonic Micro-arc Oxidation

Pure magnesium would be most development potential biomedical materials and become the hotspot of domestic biodegradable bone fixation repair materials due to its density and Young’s modulus next to human bones, and its biodegradability, appropriate strength and excellent biological activity. But the pure magnesium with the high degradation rate in vivo and it can’t grow with the bone tissue well, which would limit its application in clinical. Therefore, the corrosion of pure magnesium should be a key problem to be solved. The surface modification of pure magnesium was one of the most effective ways to solve this problem. Its corrosion resistance could be improved by the ultrasonic micro-arc oxidation coatings using ultrasonic micro-arc oxidation technology(hereinafter referred to as UMAO) on the pure magnesium. But the corrosion medium still could corrode magnesium substrate by the microporosity existing on the ultrasonic micro-arc oxidation coatings. To solve this problem, the article processed different composite post-treatments including phytic acid, phytic acid-silk fibroin(hereinafter referred to as SF) and NaOH-silane coupling agent(hereinafter referred to as SCA)-SF after UMAO treating on pure magnesium and the relevant post-treatment processing parameters also are optimized to achieve the regulation of biodegradability and biological activity of pure magnesium UMAO biological coating. In this experiment, the microstructure, element composition, functional group composition, adhesion force, abrasion resistance, wettability, electrochemical corrosion resistance of coatings were studied. The biological activity of coatings also were analyzed after immersed in vitro Hank’s solution. The specific conclusions are as follows:After different concentrations phytic acid processed pure magnesium UMAO coating, it could be found that with the increasing of the phytic acid concentration, the microporosity amount of UMAO coating decreased, no fracture phenomenon, more and more uniform density and coverage increases, the surface of coatings was rich in hydroxyl and phosphate. The adhesion force, the abrasion resistance and electrochemical corrosion resistance were improved, After immersed in Hank’s solution, the MgO of coatings converted to Mg(OH)2, the corrosion products combining Ca, P and other elements of Hank’s solution generated bone-like apatite. Comprehensive comparison, the concentration of phytic acid was 7.5g/L for the best. After SF solution processed the UMAO-phytic acid /7.5g/L coating for different time, it could be found that with the extension of SF solution processing time, the microporosity amount of UMAO coating decreased, more and more uniform density. The adhesion force, the abrasion resistance, wettability and electrochemical corrosion resistance were improved. After immersed in Hank’s solution 3 days, coatings generated bone-like apatite, the processing time of SF solution was 1.5h for the best. After NaOH-SCA-SF solution processed pure magnesium UMAO coating for different time, it could be found that SF solution formed a layer of film on the surface of coatings, with the extension of SF solution processing time, the porosity of the coating were filled more and more uniform density, roughness was getting better and better. The adhesion force, the abrasion resistance, wettability and electrochemical corrosion resistance all were improved.The porosity of the bio-coatings on pure magnesium UMAO coating processed by phytic acid, phytic acid-silk fibroin, silane coupling agent-silk fibroin were filled by the new material after chemical reaction and the interaction between materials. The electrochemical corrosion resistance of composite coatings were improved because coatings could prevent the corrosive medium from invading into the pure magnesium substrate. A layer of film formed and achieved the purpose of biodegradability regulation. At the same time, the biological activity of composite coatings also were improved due to excellent biological activity of the SF solution. Comprehensive comparison, the UMAO-NaOH-SCA-SF/1.5h coating had the most excellent performance.