Investigation On Technology Of Micro-Arc Oxidationon The Surface Of ZL201 Aluminum Casting Alloy

Micro-arc oxidation (MAO), an environment-protection and new surface treatment technology, was mainly used to the surface treatment of aluminum, magnesium, titanium and other light metals and their alloys, and can in-situ form ceramic coating on the surface of these alloys. The MAO technology has an obvious advantage for surface treatment on account of its direct technique characteristic. It has been paid much attention to since it was invented. However, till now the experimental research, the comperehensive analysis of influence of process parameters on multiple performances and the establishment of process mathematic model through process analysis, is very scarce, especially for aluminum casting alloys.The paper focuses on ZL201 aluminum casting alloy. By means of orthogonal regression experimental method, the paper has systematically investigated the process parameter regularity of MAO of ZL201 alloy, and its influence on coating performances. On the base of these, the process mathematic models are set up and the optimal process parameters are found. Then process mathematic models have been verified and modified with real experiments. Finally, a complete process data base, whose targets are thickness, hardness, corrosion resistance of the coating, has been established, while several standard specimens have been manufactured according to parameters from the standard process database.Ranges of the factors used in the experiment are: potassium hydroxide concentration is 0~5g/L, sodium aluminate concentration 0~10g/L, sodium silicate concentration 0~10g/L, sodium hexametaphosphate concentration 0~2g/L, sodium tetraborate concentration 0~2g/L, process time 0~200min, process current 0~5A, positive-going impulse width 100~10000μs, negative-going impulse width 100~10000μs, dead space time 50~1000μs.The processing mathematic model and processing experiment have shown that the performances of the coating can be changed by controlling the ratio of electrical parameter, operating fluid system, process time and other process parameters. At some temperature range, the temperature gives very little effect on coating performances during processing aluminum alloys with micro-arc oxidation. The coating performances are optimal when the positive-going current density is equal to or slightly less than less than the negative-going current density.The SEM images, of the surface and cross-section of the specimens treated with optimal process, show that the MAO coating is made up of two layers, the internal layer is very thin transition layer and the external layer hard ceramic layer, and there isn't any tectorium. The main compositions of the coating are Al and O, and the phase composition is mainlyα-Al2O3. The experiment gives the same results with theoretical analysis.