Research On Corrosion Resistance Of Oxidation Film And Microarc Oxidation Process Of Magnesium Alloy

Magnesium and its alloy have many excellent physical and mechanical properties,which make it valuable in a number of applications including aeronautics andastronautics, automobile manufacture, electronic communications, military affairs andmedical treatment, et al. However, their corrosion resistance and wear resistance arerather poor, which seriously hinder their further applications, the core problem of themagnesium alloy’s development and application is improve corrosion resistant and wearresistance of the magnesium alloy. By use of microarc oxidation technique, a layer ofoxidation film which have good corrosion resistance and wear resistance can be formedon magnesium alloy. Thus, this method has been generally recognized as the mostpromising surface treatment technique for magnesium alloy. At present, the research ofmagnesium alloy microarc oxidation technique is not perfect. Therefore, the furtherstudy of the microarc oxidation process and the coating formation mechanism, thesystematic study of the relations between the coating composition, structure and itsintegrated performances, will have a very important significance for the furtherdevelopment and application of microarc oxidation technique.Based on synthetic analysis of the domestic and foreign literatures, AZ63Bmagnesium alloy had been microarc oxidation processed in different electrolyte. It hasbeen analyzed the influence of each electrolyte to microarc oxidation process, the resultsshow that: Na₂SiO₃in the electrolyte can significantly improve crack defects of the micro-arcoxidation film; Na₂B₄O₇in the electrolyte can eliminate excessive concentration of spark inthe edge of the sample, and can raise the growth rate of the micro-arc oxidation film; NaOHin the electrolyte can promote the formation of he micro-arc oxidation film; triethanolaminein electrolyte can disperse the current density of the magnesium alloy’s surface, and controlcertain concentration of triethanolamine can effectively eliminate the efflorescence of themicro-arc oxidation film in the later stage of the microarc oxidation process to improve thequality of the micro-arc oxidation film. The best formula of basis of electrolyte which isavirulent, harmless and environment-friendly is determined by the orthogonalexperiment, and the basis of electrolyte is Na₂SiO₃,15g/L; Na₂B₄O₇,30g/L; NaOH,30g/L; Triethanolamine,15mL/L. At the same time, the optimizing of electric parameterand process time is accomplished by the experiment, and which is Current density,3A/dm²; Frequency,400Hz; Duty ratio,50%; Temperature,10³0℃;Time of oxidation,570s. The effect of nickel acetate on the micro-arc oxidation films of AZ63B magnesiumalloy was investigated in this paper, to further improve the corrosion resistance and wearresistance of the oxidation film. The experiment shows that a layer of coffee oxidationfilm which contained Ni2SiO4composition had been formed on the surface ofmagnesium alloy, after micro-arc oxidation in the electrolyte with0.5g/L nickelacetate.the film thickness relatively thick, the holes of othe film surface are smaller, andthe hardness of the film can achieve HV450, the corrosion resistance is more better.The tests about corrosion resistance performance of the magnesium alloy micro-arcoxidation film show that, the surface of magnesium substrate has been completelycorrosion soon in neutral salt spray; after500hours in neutral salt spray the corrosionarea ratio of the surface of oxidation film without nickel is to26.3%; the corrosion arearatio of the surface of oxidation film with nickel is to9.6%; the corrosion area ratio ofthe surface of oxidation film without nickel which is sealing by silane-treated is to0.9%;the corrosion area ratio of the surface of oxidation film with nickel which is sealing bysilane-treated is to0.1%.The study determine that the microarc oxidation process is Na₂SiO₃,15g/L; Na₂B₄O₇,30g/L; NaOH,30g/L; Triethanolamine,15mL/L; nickel acetate,0.5g/L; complexing agent,5ml/L; Current density,3A/dm²; Frequency,400Hz; Duty ratio,50%; Temperature,10³0℃;Time of oxidation,570s.