Preparation of self-healing superhydrophobic coatings on 6061 aluminum alloy

A fluorine-free self-healing superhydrophobic coating was successfully fabricated on 6061 aluminum alloy through HCl etching combined with Schiff base condensation reactions. The influence of HCl concentration on surface topography and wetting behavior was systematically evaluated. The results showed that etching with 2 M HCl for 30 min generated relatively uniform micro/nano rough structures, enabling the coating to achieve excellent water repellency with a contact angle reaching 163°. FT-IR and XPS analyses confirmed the formation of imine-bond-containing polymer networks derived from benzene-1,3,5-tricarboxaldehyde (BTA), hexamethylenediamine (HMDA), and octadecylamine (ODA). The prepared coating exhibited favorable mechanical durability and chemical stability. After 200 abrasion cycles, the surface still preserved a contact angle of approximately 144°, which further recovered to 157° after being stored under ambient conditions for 24 h. In addition, the coating maintained relatively stable wettability under alkaline conditions, while acidic environments significantly reduced the hydrophobicity due to partial hydrolysis of imine bonds and destruction of the surface rough structures. The dynamic imine bond network endowed the coating with room-temperature self-healing capability, providing an effective strategy for developing durable and fluorine-free superhydrophobic aluminum alloy surfaces.