Preparing a Superhydrophobic Coating with Anti-corrosion and Drag-Reduction Properties on an Aluminum Substrate

Underwater vehicles can conduct underwater exploration and military rescue operations and play a significant role in marine economic development and national defense. The fluid resistance control and corrosion resistance of underwater vehicles are essential indexes for evaluating the performance of underwater vehicles in particular marine environments and harsh conditions. The 7075 aluminum alloy, widely used in spacecraft shells, was selected as the material. We prepared a drag-reduction and robust surface based on shark skin by laser-ablation and plasma electrolytic oxidation. Then, the surface free energy was further modified by chemical modification. The ceramic coating exhibited superhydrophobicity with a water contact angle of 155.6° and roll-off angle (RA) of 5.5°. Compared with Bare Al, the corrosion current density of the superhydrophobic ceramic coating was reduced by 4 orders of magnitude since ZnO-NPs could notably enhance the corrosion resistance of Al alloys. Moreover, due to the protective effect of the ceramic coating and microstructure, the superhydrophobic coating exhibited excellent mechanical durability. Based on numerical simulation, the drag reduction effect of biomimetic microstructure under different Reynolds numbers was investigated. The experimental results indicated that biomimetic microstructure demonstrated notable drag reduction capabilities compared to smooth surfaces, stabilizing at approximately 28% during laminar flow states. Thus, applying this coating method to the underwater vehicle shell was expected to reduce the fluid resistance and extend the operational lifespan in the marine corrosive environment.