Effect Of High Temperature Oxidation Film And Voltage Raising Rate On Micro-arc Oxidation On Aluminum Alloy

In this paper, the specimens of aluminum alloy6061were treated by WH-1Amicro-arc oxidation device. This paper is composed of two parts. First, the hightemperature oxidation film was prefabricated on the specimen before the MAO treatment,the effect of the pre-film on microstructure and corrosion behavior of micro-arc oxidationcoating on6061aluminum alloy were studied, and the formation mechanism of ceramicparticles, crack and hole were investigated by the tracing role of Mg in the coating.Second, the effect of voltage rising rate on MAO was studied under the constant regime.The results show that a large amount of Mg exists in the prefabricated film, while thecontent of Mg decreases in the substrate. In the initial stage of MAO process, there aremany Mg in the ceramic coating, and the surface undulation and discreteness of MAOcoating are severe; with the increase of time, the content of Mg in the coating decreases; inthe latter stage, the content of Mg is similar with that of the content in the MAO coatingwithout pre-film, and the coating is less compact; with the high temperature oxidationtreatment, the thickness does not increase clearly, and the corrosion resistance decreases;XRD testing shows that the main phases in the coating at initial stage were MgO·Al2O3and MgO, the melting point of the mixture material was lower, leading to the decrease ofthe viscosity, all these promote the formation of the larger oxide particles; the crack tendto form at the region where the content of Mg changes dramatically; The holes formed onthe specimens can be attributed to two reasons, one is the discharge channel of breakdownthat connected to the surface of the coating, and the other is the residual concave regiondue to the imperfect connection of the oxide on the surface of the coating.Under constant regime, in the voltage rising stage, the current-time curves exist aturning point, the time, the voltage and the current corresponding to the turning point werethe arc starting time, the arc starting voltage and the arc starting current; with the increaseof voltage rising rate, the arc starting time decreases, the arc starting current increases, andthe arc starting voltage firstly increases and then decreases; for the MAO process with lowvoltage rising rate, the breakdown holes appeared at the surface of coating at the arc starting time, and the sparking were main due to the breakdown of the oxide film; for theMAO process with high voltage rising rate, the breakdown hole did not appear at thesurface of coating at the arc starting time, and the sparking were main due to thebreakdown of the gas.