Study of the Corrosion Resistance of a Superhydrophobic Ni-P-Al2O3 Composite Coating Based on Electrochemical Machining

To enhance the corrosion resistance of type 45 steel substrates, a superhydrophobic Ni-P-Al2O3 composite coating was prepared on the type 45 steel substrates with electrochemical machining. The surface morphology, surface roughness, wettability and corrosion resistance of the coating were investigated by using scanning electron microscopy, laser scanning confocal microscopy, optical contact angle measurements and electrochemical analysis. The results show that an irregular micropit structure is obtained after the Ni-P-Al2O3 composite coating was prepared by electrochemical dissolution and fluorosilane modification. There is an obvious increase in the surface roughness of the Ni-P-Al2O3 composite coating. The water contact angle reaches 152.3 degrees on the coating surface. After 25 days, a high hydrophobicity remains, and the water contact angle is 153.4 degrees. Approximately 89.72% of the droplet volume is in contact with air. The superhydrophobic Ni-P-Al2O3 composite coating exhibits a higher corrosion potential of E-corr=-0.282 V and a lower corrosion current density of J(corr)=7.018 x 10(-7) A/cm(2) compared to the type 45 steel substrates. The polarization curves of the coating at different times were studied in a 5 wt% NaCl solution to investigate the stability of the superhydrophobic Ni-P-Al2O3 composite coating. The maximum corrosion current density of the superhydrophobic Ni-P-Al2O3 composite coating is 10.254 x 10(-6) A/cm(2), and the corrosion rate is 0.124 mm/year. The superhydrophobic Ni-P-Al2O3 composite coating has excellent corrosion resistance.