Study On Novel Protective Coating Technology For Aluminum Alloy And Its Corrosion Resistance Mechanism

Aluminum alloy has been widely used in aviation,high-speed railway,architecture,and military industry etc.,because of some significant advantages,including high specific strength,specific stiffness and excellent processing performance.A thin oxide film usually forms on aluminum alloy in air condition which can provide some corrosion protection,but in harsh environments,the oxide film on Al alloy is easy to corrode and destroy because of its corrosion active characteristic.Therefore,strict corrosion protection measures should be applied to aluminum alloy in all practical application.The anodic oxidization and organic coatings are usually used for corrosion protection of aluminum alloy,based on the barrier effect of organic coating and Al2O3 oxide film can isolate aluminum alloy and corrosion environments,prolonging the service life of aluminum alloy.Strong adhesion between organic coating and aluminum alloy surface is a crucial point to maintain the organic coating with long-term corrosion protection for aluminum alloy.However,the adhesion of general organic coatings directly coated on the surface of aluminum alloy is lower.How to enhance the adhesion between organic coating and aluminum alloy surface and to improve the corrosion resistance is still facing a challenge.In this work,we focused our research on developing various surface modifications of aluminum alloy to enhance the interaction of modified polyurethane coating and aluminum alloy,by mechanical interlocking,physical adsorption and chemical reactions,and to improve the adhesion and corrosion resistance of the modified polyurethane coating coated aluminum alloy.The main progress and results are listed as follows:(1).By controlling the anodized voltage,various porous anodic oxidation films of 5 V,10V,15V and 20V were constructed on the surface of the aluminum allo y.It found that with the increase of voltage,the pore size and pore density of the oxide film increased,and the aluminum alloy anodized at 15V for 30min showed the best corrosion resistance.Anodic oxidation treatment can improve the surface roughness and wettability of aluminum alloy.With the increase of anodic oxidation voltage,the roughness and wettability increase gradually.The mechanical interlocking and physical adsorption between the modified polyurethane coating and aluminum alloy were enhanced,which improved the adhesion of the modified polyurethane coating to the surface of aluminum alloy.The dry adhesion of the modified polyurethane coating on the anodized surface of 15V and 20V aluminum alloy samples reached 15MPa,and the wet adhesion after 1200h salt spray reached 13MPa.The electrochemical impedance spectroscopy(EIS)and neutral salt spray(NSS)results showed that the anodized film/modified polyurethane coating system obtained by anodizing aluminum alloy at 15V voltage had the best corrosion resistance(2).A composite film comprised mussel adhesion protein/CeO2/3aminopropyltriethoxysilane(MCA)was developed and modified on the surface of aluminum alloy by layer-layer dipping method.The measurements of EIS and SRET demonstrated that the MCA composite film on anodic oxidized A1 possessed selfhealing function and pro vided effective protection against early corrosion of aluminum alloy.The combination of anodic oxidation treatment and MCA composite film modification could improve the surface roughness of aluminum alloy and enhance the surface wettability and surface polarity,which significantly enhance interaction of the modified polyurethane coating and aluminum alloy through mechanical interlocking and physical adsorption and chemical reactions.It was indicated that the dry adhesion of anodized film/MCA composite film/modified polyurethane coating system reached 17MPa,and the wet adhesion after 1200h salt spray reached 13MPa.The evaluation of EIS and NSS showed that the anodized film/MCA composite film/modified polyurethane coating system had excellent corrosion protection performance,which could be applied in long-term corrosion protection of aluminum alloy in harsh environments...