Microstructure And Property Of Micro-arc Oxidation Coating On Aluminum Alloy

Aluminium products are one of the most widely used materials. However, lower sruface hardness, corrosion resistance and poor wear resistance have restricted the application of aluminum alloys. Surface treatments can be employed to improve their comprehensive performance.Micro-arc oxidation, also known as micro-plasma oxidation or anodic spark deposition, has been used to prepare ceramic coatings on the surfaces of valve metals and their alloys by controlling the electrolyte and the corresponding electrical parameters. By means of the MAO technique, high-quality coatings with high microhardness, strong adhesion, and high corrosion resistance can be obtained. The coating can be used in many fields, such as automotive, aerospace, medical, and textile engineering, etc.In this paper, the ceramic oxidized coatings were prepared on2A12alloy by micro-arc oxidation in soluble AcNa electrolyte system. The effects of electrolyte composition and electrical parameters on coating microstructure and performance were studied. The phase, surface components, and composition are analyzed by XRD, SEM, and EDS, respectively. The thickness, corrosion-resistance and interfacial adhesion are measured by eddy current thickness meter, electrochemical workstation, and scratch test, respectively. Then an electrolyte system is chosen, in which the prepared coatings have excellent properties.The experiment results shows that the ceramic coatings can be formed in AcNa-NaF system and AcNa-Na2WO4system. In the AcNa-NaF system, the coating surface is rough, loose, and easy desquamated, and XRD analysis shows that the coatings are mainly composed of α-Al2O3and γ-Al2O3. F" ions have not been detected. Meanwhile in the AcNa-Na2WO4system, the coating surface is rough, but tough. Compared with the phase composition of the coatings formed in AcNa-NaF system there are W, WO3, and W18O49expect for (α-Al2O3and γ-Al2O3,. The MAO coatings formed in electrolyte of12g/L AcNa and3g/L Na2WO4are smooth and compact, and also it has less micropores and higher adhesion value. On this basis, the introduction of2g/L KOH can improve the surface quality, the interfacial adhesion and corrosion-resistance. But there still are some microcracks, and the introduction of H3BO4have not improved the surface morphology. With the addition of H3BO4, the number of microcracks reduce, and the coating corrosion-resistance are enhanced.In constant voltage mode, with the increase of positive voltage, the coatings become thicker. First, both the interfacial adhesion strength and the coatings corrosion-resistance are enhanced, and with the increase of positive voltage, both the interfacial adhesion strength and the coatings corrosion-resistance reduce. The coatings prepared at voltage500V have high interfacial adhesion strength and high corrosion-resistance. With increasing frequency, the coatings become thicker. Meanwhile the micropores size becomes smaller. And the interfacial adhesion strength and the coatings corrosion-resistance are also enhanced at first, but then reduce. The coatings with high interfacial adhesion strength and high corrosion-resistance are prepared at300Hz.