Research Of Silane Treatment And Coating Technology On The Surface Of Aluminum Alloy

Silane treatment technology is a new green surface treatment technology risen in recent years, with the advantages of low cost, green environment protection, wide application as well as excellent corrosion resistance. Silane treatment technology has become a hot research scholars, can effectively replace chromate conversion process and phosphating process with serious pollution to the environment. At present, this technology has been applied on the steel,but there is few application on aluminium alloy, the film corrosion resistance between silane and traditional metal surface treatment process—chromate conversion process and phosphating process has a certain gap, processing fluid instability, these problem limits the application of this technology. In this article, the silane treatment process has been systematic researched, the technological parameters of silane concentration, pH value and the hydrolysis time are studied, preparation technology and performance of the film in this system is optimized, at the same time, by adding rare earth additive to improve the performance of the silane film.This paper selects silane coupling agent KH-550 for surface treatment of aluminum alloy substrate, silane hydrolysis process, the preparation and modification of silane film, as well as coating process are studied. Electrical conductivity test method is used to on-line monitoring the silane solution hydrolysis process. At the same time, the composition of silane solution, hydrolysis time, solution pH are analysed by the method of single factor variables and orthogonal test method, the experimental results show that the best parameter values are the KH-550/ethanol/deionized water for 5/35/60, hydrolysis for 4h, the pH for 7.Single factor variable method is used to study the film forming technology of silane coupling agent KH-550 on the surface of the aluminum alloy matrix, using CUSO4 spot test to obtain dip time, and using the electrochemical polarization curve test to acquire the best value of curing time and curing temperature, thus to determine the best film forming technology of the silane film. The results show that the aluminum alloy matrix in silane solution dip-coating for 60s, then heating up to 180℃ for 40 mins in the electrothermal blowing dry box, the silane film has good corrosion resistance, and the polarization curve test concludes that the corrosion current density (Icorr) is 3.043*10-7 A/cm2, the corrosion potential (Ecorr) is 0.607V. The corrosion current density (Icorr) of blank sample is 1.262* 10’5 A/cm2, the corrosion potential (Ecorr) is 0.931V. Therefore, the silane film can significantly improve the corrosion resistance of aluminum alloy matrix. In the brine immersion experiments, compared with the blank substrate, silane film can effectively block the invasion of the corrosive medium, play an important role in anti-corrosion. Hydrophobic experiments show that the silane film coating can significantly increase the contact angle of the substrate surface, improve the hydrophobic property of the matrix, in the contrast of blank substrate and silane film, hydrophobic angle increase from 12.51° to 54.02°. By using SEM and EDS, silane film morphology and composition are analyzed, and the surface of the matrix is filled with silane film and level up the film, to form a uniform and compact film layer composed of C, O and Si elements on the metal surface.Single factor variable method is also used to study the silane coupling agent modification, by adding rare earth cerium salt to enhance the corrosion resistance of the silane film, the optimal doping concentration is 5×10-1g/L by one-step method, the CUSO4 spot test and electrochemical test results show that the matrix has good corrosion resistance and superior to traditional silane film. In the brine immersion experiments, the corrosion resistance of modification silane film is superior to the traditional silane film, has better protection effect of matrix. By using SEM and EDS, the morphology and composition of silane film with cerium salt modification are analyzed, film surface evenly dispersed with fine particulate matter contained Ce elements analysed by EDS. At the same time, in the laser confocal microscopic analysis map, adding cerium salt can significantly increase the membrane layer thickness, play a positive role in preventing the invasion of corrosive medium, which can increase the corrosion resistance of the membrane layer to a certain extent.In general, after the substrate coated with silane film, the outermost layer also coated with organic coating for protection or decoration, the electrophoresis method is used in this paper, then testing its corrosion resistance by salt spray test, and the organic coating can significantly increase the corrosion resistance of the matrix. The cross experiment of metal is used to test binding force between metal and organic coating, we know from the results that the silane film as an intermediary can significantly increase the bonding force between the metal and organic coating, bonding strength between the layers up to 0 degree.