| Aluminum alloys are widely in automobile field industry due to their high strength to weight ratio and light.It is significant to improve the corrosion resistance of aluminum alloy surface and its adhesion strength of the film.5182 aluminum alloy for vehicle was researchedbyscanningelectronmicroscopy?SEM?,ultramicrotomy,energy dispersive X-Ray spectroscopy?EDS??Ultra Nano hardness tester?Electrochemical impedance spectroscopy?EIS?and Scanning Kelvin probe force microscope?SKPFM?.The effects of silane treatment,zirconium conversion treatment and anodizing on the corrosion resistance of the alloy and its adhesion strength to the film were investigated.The related results were as follows:?1?The results indicate that a homogeneous coating is formed on the alloy with immersion time of 180 s,pH of 11 and curing temperature of 90?.Thickness of the silane film is about 100 nm.In the Na2B4O7·10H2O and NaOH solution,the low frequency impedance of silane treated sample is about 2 orders of magnitude higher than that of the un-treated sample.Besides,the adhesion property of the silane treated sample to organic coating is also much better than the un-treated sample.?2?It was found that a conversion coating of 50-100 nm thickness was formed on the alloy substrate under optimized conditions?immersion time of 2.5 min and pH of 4.5?and the conversion coating was preferentially formed on cathodic particles.Electrochemical impedance spectroscopy?EIS?indicates that,in the Na2B4O7·10H2O and NaOH mixed solution,the low frequency impedance of zirconium conversion treated sample is about 80?higher than that of the un-treated sample.The scratching test showed that the critical load of the zirconium-treated sample is about 75%higher than that of the etched one.After adding the film promoter(Mn2+and NaF)in the conventional zirconification solution,it is beneficial to the thickening of the zirconium film,which further enhances the corrosion resistance of the zirconium and the adhesion of the paint film.?3?Etched aluminum alloy was anodized at a constant voltage of 15V for 20min in the 170g/L sulfuric acid,with increasing anodization temperature,film growth rate increased firstly and then decreased.The corrosion resistance of anodic film is the best at25?anodization temperature.with increasing of concentration of tartaric acid?0mol/L0.9 mol/L?,growth rate of anodic film from 14.3nm/s to 18.9nm/s.Tartaric acid is added into sulfuric acid solution,which can improve the efficiency and reduce the dissolution rate of the anodic film.As the concentration of sulfuric acid decreased,the efficiency of anodic oxidation film decreased and the dissolution rate of the oxide film decreased.The anodizing improves the impedance of surface of 5182 aluminum alloy,and anodic film can be used as the intermediate layer to greatly improve the adhesion strength between the organic film and alloy.?4?The zirconium film and silane film can be used as the pretreatment process of automobile organic film,the processes are simple and effectively improve corrosion resistance and the adhesion between organic film and alloy.Compared with the above chemical conversion film,anodizing process need high energy consumption and high cost,but corrosion resistance of anodic film is better than those of chemical conversion films.Anodic film has hardness and wear resistance;The surface treatment process of three kinds of aluminum alloy can be selected according to the requirements of different body structure parts and cost. |
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