Preparation And Properties Of Rare Earth Hydrophobic Film On Aluminum Alloy

Aluminum alloy is one of the most widely used metal materials at present,but its active chemical property lead to poor corrosion resistance.In this paper,the rare earth super-hydrophobic film on aluminum alloy was prepared by combining the super-hydrophobic technology with the rare earth conversion film processing technology.The corrosion resistance of rare earth conversion coating on aluminum alloy was evaluated by CuSO₄ drop test,the hydrophobicity of the coating was evaluated by static contact angle test,the electrochemical behavior of the coating was analyzed by electrochemical method and the structure and composition of the film were analyzed by SEM,XRD,EDS and XPS.And the optimum parameters were determined.The optimum formulation of rare earth conversion coating for aluminum alloy is7g/L CeCl₃?7H₂O,6.5%H₂O₂ and 40°C.At this time,the experimental time of Ce conversion film is 85s.The corrosion resistance and self-corrosion potential of aluminum alloy are greatly increased,and the corrosion current density decreases from 9.0×10^-6A/cm² to 5.2×10^-6 A/cm²,indicating good corrosion resistance of aluminum alloy.The Ce conversion film of aluminum alloy is mainly composed of amorphous cerium oxide and hydroxide.Rare earth hydrophobic films on aluminum alloys were prepared by two-step modification method.The contact angle of the surface is 151.8±2.8°after soaking in0.02mol/L STA ethanol solution.Hydrophobic films are first formed around the structure of rare earth conversion films on the surface of aluminum alloys.Then,a two-dimensional growth is carried out along the surface of the rare earth conversion film until completely covered on the surface of the sample.The surface of the hydrophobic conversion film has a spherical structure,which is distributed uniformly on the surface of the film in the form of clusters.After hydrophobic treatment,the corrosion current density is 1.5×10^-6 A/cm²,which has good corrosion resistance and durability.Rare earth hydrophobic films on aluminum alloys were prepared by two-step electrodeposition method.The optimal formulation is 3mmol/L MnCl₂?4H₂O,2mmol/L STA,28V and 20min,when the contact angle reached 126.4±7.2°.Firstly,the film grows around the structure of Ce conversion film on the surface of aluminum alloy,and clusters are formed on the surface of rare earth conversion film,exhibiting uneven defects,which resulting in poor hydrophobicity.The main compositions of the film are Mn(C₁₇H₃₅COO)₂,Ce(C₁₇H₃₅COO)₃ and Ce(C₁₇H₃₅COO)₄,which has good corrosion resistance but poor durability.Rare earth hydrophobic films on aluminum alloy were prepared by one-step electrodeposition method.The optimal formulation is 1mmol/L MnCl₂?4H₂O,2mmol/L STA,3.5mmol/L CeCl₃?7H₂O,22V and 20min.The static contact angle of the film is160.0±3.7°,and the surface of the film with cell-like structure is micro-nano scale.The main components are Mn(C₁₇H₃₅COO)₂ and Ce(C₁₇H₃₅COO)₃ with good electrochemical performance and durability,to meet the requirements of corrosion resistance in the marine environment.In one-step electrodeposition process,the hydrophobic film is grown simultaneously with multiple layers,which has the advantages of short preparation time and good performance.