Study On The Organic-sealing Process Of Micro-arc Oxidation Coating On 2A12 Aluminum Alloy

Micro arc oxidation coating, which is prepared by micro arc oxidation technology on aluminum alloy, inevitably has micro pores and cracks which will affect the corrosion resistance of materials. In order to improve the corrosion resistance of micro arc oxidation coatings, it needs to seal treatment before its use.In this paper, Epoxy resin sealing treatment and Polyacrylamide LPS system sealing treatment have been established to study the micro arc oxidation coating of 2A12 alloy. Scanning electron microscopy and X-ray diffraction were used to study the morphology and composition of the pre and post micro arc oxidation coating sealing. The solution ratio and the best recipe for preparing LPS system was optimized by orthogonal test. Electrochemical workstation was applied to analyze the corrosion resistance of the pre and post micro arc oxidation coating sealing.The results show that: The epoxy resin can be well sealed the residual micro pores and micro cracks which are produced in the process of micro arc oxidation, which greatly improve the corrosion resistance of micro arc oxidation coatings. The higher the voltage of micro arc oxidation, the better the sealing effect of the epoxy resin on the micro arc oxidation coatings; however, when the voltage rises to a certain extent, micro pores on the surface of coating become larger, micro cracks increase and they turn deeper, the effect of epoxy resin sealing the micro-pores and micro cracks becomes poor. Polarization curves of the micro arc oxidation coatings which are prepared at the micro arc oxidation voltage of 350 V and 450 V respectively are almost coincident, that is to say, the corrosion resistance of the micro arc oxidation coatings has not been greatly improved. Polyacrylamide LPS system has an effective influence on sealing micro pores and micro cracks which are produced in the process of micro arc oxidation, the effect of sealing micro-holes on the corrosion resistance of the micro arc oxidation coatings is remarkable. The study on the temperature and time factor of the hole-sealing shows that: if the temperature is low, the degree of hydrolysis of polyacrylamide will be not sufficient, which eventually leads to inadequate cross-linking reaction and makes the corrosion resistance of micro arc oxidation coating poor. On the other hand, if the sealing time is too long, Polyacrylamide is prone to excessive cross-linking and forms molecular aggregation on the surface of micro arc oxidation coatings, which is also not conducive to the improvement of corrosion resistance. Therefore, the optimum sealing process parameters are 60℃ and 60 min. In this study, it is also found that the cross-linking rate of polyacrylamide can be effectively slowed down by additives, such as triethanolamine and sulfocarbamide, remission effect indicates that the former is better than the latter. The sealed-coatings was soaked in 3.5%NaCl solution, its EIS test results show that: the epoxy resin coating and polyacrylamide coating play a great role in blocking corrosion medium, and the corrosive medium can only be diffused into the interface between the loose layer and the dense layer, thus greatly slow down the corrosion rate.