Strategies to improve the anti-corrosion of Al alloy substrate effectively by reinforced double interfacial adhesion and enhanced penetration resistance of labyrinth effect

In this paper, reinforced double interfacial constructions were fabricated by in situ growing appropriate coarse surfaces of layered double hydroxide (LDH) layers in mostly verticals orientation from Al alloy substrate, and then by depositing organic coatings of fluororesin through electrostatic spraying with LDH nanosheets that in mostly horizontal orientation onto LDH layers. The double interface structures consisting of coatings/LDH intermediate layers/alloy substrate realized the remarkable improvement of adhesion retention through the in-situ hydrothermal growth mechanism of LDH layers and the formation of mechanical interlocking and chemical bonding (C-O-Mg). In the adhesion strength tests, it was observed that the stripping areas of anti-corrosion coatings on the single interfacial structure of coatings/alloy substrate reached 16 % after the scratching, and then increased to 40 % after the tape peeling. However, no stripping occurred on the anti-corrosion coatings on the double interfacial structure. Moreover, the “labyrinth effect” produced by LDH nanosheets covered in horizon orientations could delay the invasion of water molecules (corrosive medium) more effectively than that of nanoparticles that in random distribution. Therefore, compared with that of the nanoparticles/fluororesin coating (2.814 × 10⁵ Ω·cm²), the |Z|_0.1Hz of the nanosheets/fluororesin coating increased by an order of magnitude, reaching a value of 1.020 × 10⁶ Ω·cm². After five friction cycles, the nanosheets/fluororesin coating maintained a larger water contact angle (117.20°) than the nanoparticles/fluororesin coating (108.49°), which indicated its superior mechanical stability. The works gave possible strategy enhance interfacial adhesion and permeability resistance of anti-corrosion coatings and enlarge applicable fields for both active metals and light alloys.