Study On Anodic Oxidation Of High Silicon Aluminum Alloy And Sealing Methods For Its Anodic Film

Research object of this paper is a new aluminum alloy material that is high silicon aluminum alloy, and the silicon content of this new material is up to13%～15%. Therefore, comparing with other traditional materials, it has had more advantages such as high strength and especial plasticity.In this paper, the sulfuric acid has been used as the basis anodizing electrolyte, and anodizing temperature, time and current density has also been identified. On this basis, this paper has selected three different organic acids as additive of anodizing electrolyte and discussed the effect of the concentration of organic acids on the oxide film’s quality and growth. Therefore, the best concentration of organic acids was confirmed:5g/L oxalic acid,15g/L citric acid and5g/L tartaric acid.Through potassium dichromate spot test, NSS and polarization curve test, the anodic oxide films of four kinds of electrolytes were studied. The experimental results indicated that anodic oxide film’s corrosion resistance of the electrolyte adding organic acid is better than sulfuric. Moreover, the corrosion resistance of the anodic film adding citric acid in sulfuric is best. Based on above researches, SEM, XRD and EDS were employed to study the morphology, interface, structure and elements of the anodic films. The results showed that the anodic film is composed of amorphous alumina. And organic acids could not change the structure and composition of the film, but organic acids increased the film thickness, the citric acid helps greatly to increase the thickness of anodic film.This paper also studied the sealing process of oxide film on high silicon aluminum alloy. Based on the sealing mechanism, this paper researched that the effects of concentration of stearic acid, sealing time and sealing temperature on the anodic oxide film’s corrosion resistance, and the optimum formula is100%stearic acid concentration,45min sealing time and95℃sealing temperature. Hence, the optimum technological condition of this sealing method was determined. SEM and EDS were employed to study the morphology, interface, structure and elements of anodic film. The results showed that the film appear carbon on surface after sealing.Through immersion corrosion experiment, sodium hydroxide dropping test and polarization curve, the corrosion resistance of anodic oxide films after different sealing methods was studied. The results revealed that anodic oxide films after stearic acid sealing method had the best corrosion resistance ability. The sealing methods included that heat sealing, cold sealing, nickel acetate sealing, dichromate sealing and stearic acid sealing. The morphology of anodic oxide film after sealing had been systematically analyzed through SEM, and the analysis results indicate that the surface of anodic oxide film was improved after sealing.