Preparation And Properties Of Modified Aluminum Phosphate Protective Coatings On High Strength Steel Surface

Aimed at the problem of corrosion resistance,brittleness and low strength of the aluminum containing phosphate coating on the landing gear surface,a modified inorganic phosphate protective coating primer and topcoat were designed in this paper.Two kinds of coatings were prepared on the surface of high strength steel by air spraying.The coating formulations were established by orthogonal experiments.The surface morphology,thickness,hardness and adhesion of the coating were tested and analyzed.The corrosion resistance of modified primer was analyzed by neutral salt spray test,simulated seawater immersion test and electrochemical test.The wear resistance of modified topcoat was analyzed by friction and wear test.The result shows that the modified primer formulation optimized by orthogonal test is: Al(H2PO4)3: ZnO: MgO: MgCrO4: Al: Zn: H2O=15: 0.3: 0.3: 0.8: 2.5: 1.5: 10.The modified topcoat formulation is Al(H2PO4)3: ZnO: MgO: MgCrO4: Al: C: H2O=15: 0.3: 0.3: 1.6: 5.5: 0.09: 10.According to GB to measure the basic physical properties of the coating.The thickness of modified primer is 50?m,the hardness is 2H,and the adhesion is two.The thickness of modified topcoat is 40?m,the hardness is 3H,and the adhesion is two.The corrosion resistance of the modified primer show that no significant change in the surface of the primer after 1000 h Neutral salt spray test.After 21 days full immersion test,there is not obvious corrosion occurring on the surface coating.In electrochemical test,The corrosion potentials of the primer before and after modification were-0.545 V and-0.783 V,and the cathodic protection is provided for the substrate.The impedance spectrum of the coating reflects the four stages of the anticorrosion process of the coating,mainly for the sacrificial anodic effect and the shielding effect of corrosion products.The addition of zinc powder makes the anti-corrosion performance of the primer greatly improved.The results show that the addition of graphene decreases the friction coefficient of the topcoat,reduces the wear volume,and improves the wear resistance.The modified topcoat in the load of the friction coefficient is reduced by about 30% under the 200r/min speed.The wear volume decreases with the load increasing,and the wear amount decreases by 36.9% under 250 g load.Under the conditions of 200r/min and a load of 200 g,the main wear mechanism of the modified topcoat is abrasive wear,and the main wear mechanism of the unmodified topcoat is adhesive wear.