Preparation And Properties Of Low Pressure Cold Spraying Al Based Coating-anodic Oxide Film Composite Coating

7075 aluminum alloy,due to its high strength/weight ratio,is widely used as structural components in aircraft manufacturing and other industries.These structural parts are of special service environment and are subjected to salt spray or seawater erosion for a long time.These parts may be affected by various corrosion,such as pitting and galvanic corrosion,intergranular corrosion,stress cracking corrosion and peeling corrosion.The replacement cost of large-scale components after local damage is huge.It is an important way to solve these problems to adopt reasonable local repair methods.Therefore,how to repair the corroded and worn aluminum alloy to prolong its service time is of great significance.In this paper,low pressure cold spraying method was used to deposit aluminum based coating on 7075 aluminum alloy.The composite coating of cold spraying aluminum based coating and anodic oxide film was obtained by optimizing the process parameters of anodic oxidation treatment on the aluminum based coating,and then the properties of the composite coating were enhanced by graphene modification and in-situ shot peening respectively.The micro morphology,structure,composition and microstructure of the coating were characterized by SEM,XRD and Raman.The tribological behavior of the composite coating at room temperature and its corrosion resistance in corrosive environment were studied.The main work of this paper is as follows:1.Al-20%Al₂O₃mixed powder was prepared by mechanical mixing method.Aluminum based coating was prepared on the surface of 7075 aluminum alloy by low pressure cold spraying technology.The coating surface was anodized to form an oxide film.The effects of H₂SO₄concentration,voltage intensity and oxidation time on the structure and properties of the anodic oxide film were discussed.The results show that with the increase of sulfuric acid concentration,the surface hardness of the anodic oxide film increases.When the sulfuric acid concentration is 10%,the hardness of the film is the highest and the wear resistance is the best.With the increase of electric voltage,cracks appear on the surface of the oxide film.When the voltage is 25V,the structure of the anodic oxide film is complete With the increase of oxidation time,the hardness of anodic oxide film first increases and then decreases,and the anodic oxide film shows the best wear resistance when the reaction time is 60 min.The results show that the optimum process of anodizing is sulfuric acid concentration of 10%,voltage strength of 25V and anodizing time of 60min.2.The microstructure of G/Al-AAO composite coating was analyzed.The results showed that graphene was evenly distributed on the surface of the anodized film.The addition of graphene improved the quality of the anodized film,especially in the reduction of defects and cracks.The results show that the self corrosion potential of G/Al-AAO is positively shifted by 0.139 VSCE and the self corrosion current density is reduced by nearly 16 times compared with Al-AAO,which indicates that the corrosion protection performance of the composite coating is enhanced by the addition of reduced graphene oxide;meanwhile,the friction coefficient of G/Al-AAO is significantly reduced to 0.26 and the wear rate is reduced by 50%,which indicates that the addition of graphene enhances the corrosion protection performance of the composite coating The friction reduction and wear resistance of the composite coating were studied.3.The in-situ shot peening effect was combined with the cold spraying process.By adding 20%?60%(mass fraction)large size shot peening particles into the spraying powder,the densified aluminum coating was prepared by means of the in-situ forging effect on the deposited aluminum coating during the spraying process.Then the aluminum coating surface was anodized,and finally the aluminum based coating anodic oxidation film composite coating was formed.The results show that with the increase of stainless steel shot peening particles,the forging effect is enhanced,and the structure of the composite coating is more compact;in the friction test,it shows lower friction coefficient and lower wear rate;in the corrosive environment,it has high thermodynamic stability and dynamic stability,specifically with the highest self corrosion potential and the lowest self corrosion current density.