Study On The Performances Of AZ91D Magnesium Alloy With And Without Micro-arc Oxidation Coating In Oral Environment

Magnesium is an exceptionally lightweight metal as the "21st century the most potential for development and future of the green engineering materials".It presents a great potential as medical implant material in our body,such as low price,good biocompatibility, good biodegradability as well as participates the metabolism as the positive ion which just inferior to potassium ion,sodium ion and calcium ion in the cell.However,the chemical property of magnesium alloy is so active that it has to suffering the challenge for meeting the requirements of corrosion resistance,abrasion resistance and fatigue resistance.So some surface treatments should be applied to meet the use of long-term implantation. Micro-arc oxidation(MAO)present a great potential as a surface treatment technology, through MAO,in-situ-grown ceramic coating is directly formed on the surface of magnesium alloy,by which its corrosion resistance,abrasion resistance and fatigue resistance are greatly improved.This research will introduce the AZ91D magnesium alloy into the field of oral implants,Micro-arc oxidation technology will be used to AZ91D magnesium alloy surface modification.With the method of experiment and numerical modeling,the corrosion resistance,abrasion resistance and fatigue resistance of AZ91D magnesium alloy with and without Micro-arc Oxidation Coating in oral environment is studied.The main results are as follows:(1)The corrosion resistance of AZ91D magnesium alloy with and without Micro-arc Oxidation Coating is investigated under the experiments of immersion corrosion and electrochemical corrosion.The result indicates that in the immersion corrosion experiment, within 60 days,the weightlessness of untreated samples is 20.97 times that of micro-arc samples,the electrochemical corrosion experiment enhanced the corrosion electric potential E₀ of AZ91D magnesium alloy from-1.45V which without Micro-arc Oxidation Coating in artificial saliva to -0.44V which with Micro-arc Oxidation,corrosion current density I₀ from 7.5×10^-5A/cm² without Micro-arc Oxidation Coating to 5.0×10^-7A/cm² with Micro-arc Oxidation.The corrosion resistance of AZ91D magnesium alloy is greatly improved with Micro-arc Oxidation Coating.(2)The X-ray diffraction(XRD)analysis shows the ceramic coating is mainly composed of some oxides which are similar to spine,such as Mg₂Al₄Si₅O₁₈, Mg_0.87Al_1.83O_3.61,MgSiO₃ and Mg₂Al.Besides this,the ceramic coating also contains some multiple oxides which have magnesium and aluminum in them,the ceramic coating combine tightly with magnesium alloy,it can separate corrosive agent with bulk material, improve the performance of corrosion resistance and abrasion resistance of AZ91D magnesium.(3)The abrasion resistance of AZ91D magnesium alloy with and without Micro-arc Oxidation Coating in the artificial saliva is studied by the wear experiment using the facility of MM-200 which is produced by Nanjing University of Science & Technology. The result shows that the volume loss of AZ91D magnesium alloy without Micro-arc Oxidation Coating is greater than Ti6A14V alloy,the micro-oxidation magnesium alloy is the least.The abrasion resistance of AZ91D magnesium alloy is greatly improved with Micro-arc Oxidation Coating.(4)The abrasion resistance of AZ91D magnesium alloy with and without Micro-arc Oxidation Coating in the artificial saliva is also researched by numerical simulation using the method of finite element.The result shows the similar tendency that the abrasion resistance of AZ91D magnesium alloy is greatly improved with Micro-arc Oxidation Coating.(5)After the AZ91D magnesium alloy is Micro-arc Oxidation treated,the affection to fatigue resistance of the ceramic coating's thickness and Young's modulus is studied by finite element.The conclusion is that under the specifically condition of oral environment, the thickness and Young's modulus of ceramic coating have no essential influence to the fatigue of tooth material.The model will not be destroyed under the cyclic load of infinite times in oral cavity.It is suitable to be denture material to repel fatigue.