Fabrication Of Hydroxyapatite Coating On The Surface Of Az31Magnesium Alloy By Sol-gel Technique And Research Of The Property

Magnesium alloys have become the most potential biomaterials due to itsmoderate elastic modulus, yield strength, and good biological properties.However, its application in the biological field is limited by its poor corrosionresistance, especially implanted in human body containing chloride ion. Theresearch of hydroxyapatite (HAP) coating on the surface of magnesium alloyhas attracted extensive interest because of the high stability and good corrosionresistance of HAP. There are a lot of methods of preparing HAP coating on thesurface of metal substrate, such as electrodeposition, plasma spraying, lasercladding and sol-gel technique, but these methods have both its advantages anddisadvantages. Sol-gel technique was utilized to prepare HAP coating on thesurface ofAZ31magnesium alloy due to its simple operation and low cost.In this paper, Ca(OH)2and Ca(H2PO4)2·H2O were used as raw materials toprepare HAP coating on the surface of rolled AZ31by using sol-gel technique.Phase compositions, surface morphologies and cross section, corrosionresistance and contact angle were tested by X-ray diffraction, infraredspectrometer, scanning electron microscope, electrochemical workstation andcontact angle meter, respectively. The influence of surface mechanical attritiontreatment on the surface roughness of AZ31magnesium alloy was presented.Then, HAP coating was prepared on the surface of AZ31of different roughness and the influence of different roughness on property of HAP coating was alsopresented. The study of methylcellulose as an additive to prepare HAP coatingwas also presented. The main conclusions are as follows:(1) HAP coating of high purity has been prepared on the surface of AZ31magnesium alloy by using sol-gel technique. The thickness of the coating isapproximately8μm. The coating is uneven and of high porosity and slow downthe corrosion rate of AZ31, and the hydrophilic property of HAP coating isimproved.(2) The surface roughness of substrate varies with the difference of steelball diameter. The ball diameter is bigger, the roughness is smaller. The adhesionstrength of the coating is improved when the surface roughness is enhanced. Theadhesion strength increases with the increase of surface roughness. The biggerof the roughness is, the fewer cracks there are on the surface of AZ31. Thecorrosion resistance of substrate decreases with the increase of surfaceroughness, while the corrosion resistance of magnesium alloys is improved dueto the presence of HAP coating.(3) HAP-MC composite coating of different layers has also been preparedon the surface of AZ31magnesium alloy. The composite coating is smootherand more compact than HAP coating. The thickness of composite coatingincreases with the increase of coating layer. The binding force of HAP-MCcomposite coating is relatively good, and the binding force is best when thenumber of the layer is only one. HAP-MC composite coating slows down thebiodegradation rate of AZ31in physiological saline. The more the number of thecoating is, the stronger the coating is. The immersion tests in Hank’s solutionconfirm that HAP-MC composite coating could protect AZ31substrate moreeffectively than HAP coating, which is good for the long-term use of implantmaterials.