Improve the binding force of PEEK coating with Mg surface by femtosecond lasers induced micro/nanostructures

A polymer coating is an effective approach to increase the surface wear and corrosion resistance of magnesium alloys, but the low bonding strength limits its further applications. In this study, poly-ether-ether-ketone (PEEK) coating was prepared on the AZ31 magnesium alloy. Femtosecond laser surface treatment was used to change the surface characteristics of Mg-base alloy, and the effect of the laser-induced structures on improving the bonding strength of PEEK coating was investigated. With the increase in laser energy, the gap between laser-induced nanostructures gradually increases. When V = 1000 mm s⁻¹, a uniform striped structure is formed on the surface, and the average period is about 0.5 μm. When V = 300 mm s⁻¹, the stripe breaks and grows in the length direction, and the surface texture tends to be a coral-like structure with diameter of about 7 μm. When the scanning speed is reduced to V = 200 mm s⁻¹, the grooves gradually deepen, and irregular bumped structures were formed with the spacing of about 3 ~ 5 μm. The surface roughness after laser treatment increased from 9.37 nm to 589.3 nm, and the surface of magnesium alloy changed from hydrophilic to hydrophobic. PEEK coating was prepared by electrostatic spraying. The raw PEEK is fully melted and infiltrated with the laser-induced structure matrix, resulting in a high bonding strength compared with the untreated Mg matrix. The surface of the nanostructure has excellent wettability to PEEK coating, which improves the adhesion of coating and prolongs the service life of the magnesium alloy. PEEK coating has excellent sealing effect and chemical corrosion resistance, which increases the corrosion potential on the substrate surface and the corrosion resistance. Results can provide a new approach to improve the bonding properties between metal bases and polymer coating.