Preparation Technology And Structure Of Green Oxide Film By Micro-arc Oxidation On Aluminum Alloy

Aluminum (Al) and its alloys are widely applied to construction, automotive, aerospace and ship building industries due to their excellent properties, such as low density, good electrical and thermal conductivity, good ductility, high specific strength, and easy formability etc.. However, the applications of Al and its alloys are restricted in many more industry fields owing to their poor surface hardness, corrosion resistance, wear resistance and dull color. It is of great necessity to prepare coatings with good quality and beautiful color by surface treatments. The colored coating on Al and its alloys can be prepared by traditional technologies, such as chemical coloring process, whole staining, electrocolor process, electrophoresis method andmicro-arc oxidation (MAO) and so on. Among which, MAO is a relatively new promising surface treatment technology. Coatings with strength adhesion, high surface hardness, excellent corrosion and wear resistance and adjustable surface colors can be prepared by Micro-arc oxidation.In this paper, a blue coating was prepared on 6063 aluminum alloy by MAO in NaSiO3-KOH electrolyte, C3H8O3 and KF were added into the electrolyte, and NH4VO3 was added as colorant to prepare green coating on aluminum alloy. The effects of electrolyte composition and electrical parameters on coating surface and properties were investigated. The thickness, phase composition, surface morphology, corrosion resistance and adhesion were assessed using eddy current thickness meter, X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), electrochemical corrosion test and scratch test, respectively. Then technological parameterswere chosen.Resultsshowed that the influences of NH4VO3, Na2SiO3, positive and negative voltages and positive duty ratioon coating properties were similar. As one of the above factors increased, the coating color deepened, the thickness andsurface micro-pore sizeincreased, the adhesion and corrosion resistance increasedfirstly and then decreased. With the addition of KF, the coating adhesion and corrosion resistance were improved. The green coating with high adhesion and corrosion resistancewas formedby the optimized technological parameters, which were listed as follows: NH4VO3 6g/L; Na2SiO3 8g/L; KF 0.5g/L; positive voltage 440V; negative voltage-40V; positive ratios:30%,30%. Besides, the coating presents green color because of the formation of V2O5 during the MAO reaction.