Effects Of Electrical Parameters And Their Interaction On Microstructure And Property Of MAO Coatings On Pure Aluminium

The orthogonal experiment design and data processing were applied in this paper, to study the effects of electrical parameters and their interaction on microstructure and property of MAO coatings on pure aluminium conducted in silicate electrolyte system. The thickness of coatings, the corrosion of spot test and electrochemical corrosion current were characterized by TT260 thickness gauge, spot test and electrochemical experiments. The surface morphology, cross section morphology and phase composition of the coatings were observed under SEM and XRD.The results showed that the voltage had significantly influence on thickness and drip corrosion resistance of the coatings, which had two or three orders of magnitude higher than the influence of frequency, duty ratio and interaction among electrical parameters, then frequency fellows. Duty ratio had barely influence on thickness and spot corrosion resistance of the coatings, so it is concluded that the optimal level match only appears difference in the duty ratio is negligible when thickness and spot corrosion resistance were considered separately. But it obtained the same optimal scheme while they were considered comprehensively. i.e 480 V, 700 HZ, 30 %. On the other hand, the voltage had slightly significantly influence on corrosion current density, which was influenced by a lot of integrated factors. The higher voltage, the lower compactness is, that can lead to chloride ions migrated easily through the micropore and crack defects in the electrochemical experiments, showed the bigger figure of corrosion current density and the poor corrosion resistance; On the contrary, the lower voltage, the movement of chloride ions was hindered beasuse of better compactness,then showed good corrosion resistance. So we can get the same optimal scheme when only considered the corrosion current density and comprehensively analyzed thickness and corrosion current density,i.e. 340 V, 2000 HZ, 20 %.The influence of frequency on thickness, corrosion resistance of spot test and corrosion current density were not significant. But it showed more greater influence on corrosion resistance than the thickness because of the higher frequency, the higher compactness is, which can lead to the hydrogen ion in spot test and chloride ions in electrochemical experiment are not easy to transfer in the coatings, characterized by good corrosion resistance. But the products quantity of micro-arc oxidation that react with hydrogen ion is the main reason for the corrosion resistance is good or bad. The coatings growth rate is faster under the low frequency than high frequency, which produced more oxide. So the frequency was intended to 700 HZ when only considered corrosion resistance based on spot test and 2000 HZ when only considered the electrochemical corrosion current.The influence of duty ratio on the performance of coatings was not significant, but slightly influence on corrosion current density. This was mainly because of the higher duty ratio the more crack the coatings had, which can lead to easier transference of chloride ions and the bigger corrosion current density. So 20 % was chosed when only considered corrosion current. Otherwise, the high and low levels of duty ratio both can be selected in other collocation of electrical parameters.The interaction between voltage and frequency, voltage and duty ratio, frequency and duty ratio had little influence on the performance of coatings. The effect of interaction between voltage and frequency is an order of magnitude higher on the corrosion current density than on the thickness of coatings and spot test, the influence of the interaction between voltage and duty ratio is in the same order of magnitude on three indexes of performance, the effect of interaction between frequency and duty ratio is in the same order of magnitude on thickness and corrosion current, which is an order of magnitude higher than spot test.