Effect and mechanism of pyrophosphoric acid anodizing technological parameters on the superhydrophilicity coupled corrosion resistance of aluminum alloy distillation desalination tubes

Surface superhydrophilic modification of aluminum alloy tubes in seawater distillation desalination can significantly improve the energy utilization and water production efficiency of desalination. But the relationship between superhydrophilicity and corrosion resistance of the modified surface of aluminum alloy is restricted, which has become an important problem limiting the application of superhydrophilic modified aluminum alloy distillation desalination tubes. With a simple, economical, and practical anodizing technology of pyrophosphoric acid, this research performs superhydrophilic modification on 5052 aluminum alloy, and investigates the effect and mechanism of anodizing technological parameters (time, voltage and electrolyte temperature) on the superhydrophilicity coupled corrosion resistance of aluminum alloy surface. An equivalent circuit corresponding to the electrochemical impedance spectrum of the superhydrophilic anodic oxide film is proposed, and the corrosion resistance mechanism of the superhydrophilic anodic oxide film is revealed by fitting and analysis. Then, an effective method to enhance its corrosion resistance is proposed. The results show that the corrosion resistance of superhydrophilic anodic oxide film is independent of overall film thickness, but closely related to its internal barrier layer thickness. Moreover, increasing the constant voltage during anodizing can effectively increase its internal barrier layer thickness and thereby substantially improve the corrosion resistance of the superhydrophilic anodic oxide film. When anodizing the sample at the optimum 15 °C electrolyte temperature for 20 min and increasing the applied constant voltage from 30 V to 70 V, the superhydrophilic anodic oxide film corrosion inhibition efficiency substantially improves from 36 % to 85 %. This paper provides a theoretical basis and technical guidance for manufacturing a novel of aluminum alloy distillation desalination tube with surface superhydrophilicity coupled corrosion resistance.