Preparation And Characterization Of Inorganic Aluminum Phosphate Protective Coating On High Strength Steel Surface

Aimed at the problems exist in high-strength steel surface protection technology, this project developed a kind of inorganic phosphate surface protective coating that include primer paint and finish paint. The coatings were applied by air spray and cured on the high-strength surface to provide corrosion resistant and antioxidant for high-strength steel substrate. The formula of primer paint and finish paints were optimized through orthogonal test. The coating's thickness, hardness, adhesion and surface morphology were tested; the anti-corrosion performance was tested by neutral salt fog test, simulated seawater immersion test, and electrochemical test. High temperature oxidation resistance performance was tested by 600? high temperature oxidation experiment.The result shows that the primer paint formula which is optimized by orthogonal test method is Distilled Water :Al(H2PO4)3 : ZnO : MgO : MgCrO4: Al = 30 : 15 : 0.4 : 0.4 : 3.0 : 36; The finish paint formula which is optimized by orthogonal test method is Distilled Water :Al(H2PO4)3 : ZnO : MgO : MgCrO4: Al: TEOS = 15 : 15 : 0.4 : 0.4 : 2.4 : 4.5 : 0.6. The curing process is heating coating at 120? for 2 hours, then increase to 220? for 17 hours in an oven. The thickness of the coating after primer and finish applied is 117.4?m, and the hardness is 3H, its adhesion is 10.66 MPa.The results obtained in corrosion resistance test show that after 1000 hours of neutral salt spray test, the coating does not have any obvious corrosion exist on the surface of coating, which can be proved by there being no corrosion product formation on the surface. After 21 days full immersion test, there is not obvious corrosion occurring on the surface coating, however, the waterproof performance is not good enough to keep coatings stable. In electrochemical test, coating corrosion potential was significantly higher than high-strength substrate; coating capacitance arc amplitude is larger than matrix. The excellent corrosion resistance performance of the coating is proved, and it is a an effective way to protect high-strength steel in corrosive medium. The antioxidant test results show that after 100 hours high temperature oxidation tests at 600?, coating oxidation increase is less than high-strength steel substrate during the process of test and the oxidation rate of coating is always lower than that of the substrate, the antioxidant level of coating is total antioxidant activity with excellent resistance to high temperature oxidation performance.