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

Aluminum and its alloys are widely applied to aerospace and automotive industries due to their excellent properties, such as high specific strength, light mass and easy formability. However, their extensive applications are restricted in many industry fields owing to their poor surface hardness, corrosion resistance, and wear resistance. It is of great necessity to prepare beautiful and good quality coating by surface treatment. The colored coating on Aluminum and its alloys is prepared by traditional technology, such as chemical coloring process, whole staining and electrocolor process. However, the colored coatings are rather thin and fall off easily. Micro-arc oxidation is a promising surface treatment technology evolving from conventional anodizing. A film with excellent corrosion resistance, adhesion and beautiful surface can be prepared by Micro-arc oxidation.In this paper, a blue coating was prepared on6063aluminum alloy by micro-arc oxidation (MAO) in NaSiO3-KOH electrolyte, and CoSO4was selected as colorant. 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 a technological parameter is chosen, by which the blue coating with good quality is prepared.As the experimental results suggest, the influences of NaSiO3, COSO4, positive and negative voltages on coating are similar. As its value increases, the coating color deepened, the thickness is higher, the adhesion and corrosion resistance firstly increase and then degrade, respectively. With addition of NaF, the coating presents deepened color, higher thickness, higher adhesion and corrosion resistance. With the increase of duty ratio, the color depth, thickness and corrosion resistance of coating increase, the coating adhesion firstly increase and then degrade. So the blue coating with uniform and compact surface is formed and presents high adhesion and corrosion resistance by the technological parameter as followed:NaSiO3:8g/L; KOH:1.5g/L; CoSO4:0.8g/L; NaF:0.5g/L; positive voltage:460V; negative voltage:-100V; frequency:300HZ; positive and negative duty ratios:60%,30%; duration of MAO treatment:lOmin. Besides, the result of TEM tells that the coating presents blue because of the existence of Al2CoO4.