Study On Composite Acid Anodizing And Sealing Process Of 5052 Aluminum Alloy

5052 aluminum alloy is widely used in marine engineering fields such as offshore work platforms,ships,and heat exchange tubes due to its excellent processability,weldability,and corrosion resistance.However,in the marine environment,aluminum alloy corrosion is relatively severe.Anodizing with sulfuric acid electrolyte can effectively control corrosion.In order to further improve the corrosion and wear resistance of the anodic oxidation film,we developed a three-acid system anodizing process（named TAA）applied to 5052aluminum alloy,and based on this,different sealing processes（including ultrasonic and layered double metal hydroxide（LDH））were used to seal the oxide film.The oxide film was characterized by SEM,EDS,XRD,FTIR,and XPS.The hardness,wear resistance,and corrosion resistance of the oxide film were evaluated using microhardness testers,sand drop wear tests,electrochemical testers,immersion tests,and salt spray tests.The main research results are as follows:（1）Based on sulfuric acid electrolyte,a three-acid electrolyte system was designed with hardness and corrosion resistance as indicators.The optimal process parameters for TAA were determined through orthogonal experiments.The oxide film prepared under the optimal process conditions consists of hexagonal prismatic crystal cells,with a porous layer porosity of 11.2%and a film thickness of approximately 28.5μm.The main component is amorphous Al₂O₃ and contains a small amount of C and S.Compared with sulfuric acid anodic oxidation film,TAA oxidation film has higher density,hardness,thickness,wear resistance,and corrosion resistance.The porosity of the porous layer decreased from 35.13%to 11.20%,the hardness increased from 331.21HV to 453.71 HV,and the thickness increased from 26.8μm increased to 28.5μm,the weight loss rate of the sample decreased from 0.07 mg·dm^-3 to 0.04mg·dm^-3 in the sand drop wear resistance test,and the electrochemical impedance increased by one order of magnitude（from 1.939×10⁷Ω·cm²increased to 2.471×10⁸Ω·cm²）.（2）An ultrasonic assisted boiling water sealing（UABWs）process is proposed.Compared with conventional boiling water sealing（BWs）,the oxide film treated with UABWs has higher density,hardness,wear resistance,and corrosion resistance.The hardness increased from 436.88 HV to 496.41 HV,the weight loss rate of the sample decreased from 0.05 mg·dm^-3 to 0.04 mg·dm^-3 in the sand drop wear resistance test,and the electrochemical impedance increased from 1.673×10⁸Ω·cm² increased to 1.673×10⁸Ω·cm².The results of sealing quality evaluation,immersion test,and salt spray test also indicate that the oxide film treated based on UABWs has better corrosion resistance.（3）LDH nanolayers（LDHs-NO₃^-）with NO₃^-intercalation were prepared on the surface of TAA oxide film using in-situ growth method,and VO₃^-intercalated LDH nanolayers（LDHs-VO₃^-）were obtained using ion exchange method.Compared with LDHs-NO₃^-,the oxide film treated with LDHs-VO₃^-exhibits higher corrosion resistance and an increase in electrochemical impedance by two orders of magnitude（from 9.651×10⁷Ω·cm² increased to1.121×10⁹Ω·cm²）.In addition,this article also studied the preparation of NO₃^-intercalated LDH nanolayers（BWs-LDHs-NO₃^-）on the surface of the oxide film after boiling water sealing,which also exhibited excellent corrosion resistance（the electrochemical impedance of the oxide film is 1.821×10⁸Ω·cm²）.However,the results of microhardness testing and the evaluation of the sealing quality using phosphoric acid method indicate that the oxide film after LDH sealing has certain defects,such as low hardness and poor acid resistance.