Enhanced anti-corrosion/wear properties of Mg alloy through a hierarchical bio-inspired self-healing composite coating

Abstract

The poor anti-corrosion/wear property of magnesium (Mg) alloys has limited their industrial applications. This paper reports a hierarchical bio-inspired composite coating on Mg alloy surface, through a spray/spin assisted self-assembly process, which overcomes the difficulty in coordination of the self-healing and wear resistance ability, realizing an enhanced self-healing and anti-corrosion/wear ability. The nitrogen-ligated boroxine cross-linked polydimethylsiloxane (N-B-PDMS) and the blend solution of reduced graphene oxide (RGO) and polyvinyl alcohol (PVA) are used to construct the protective hard top layer and self-healing down layer, respectively, obtaining an N-B-PDMS@RGO/PVA (B@RGO/PVA) coating. A large number of reversible covalent boroxine(B3O3)/hydrogen bonding networks are formed within the coating, leading to a compact hierarchical composite structure. The results show that the scratch is miraculously repaired within 1.5 min due to the reversible chemical bonding of N-B-PDMS coating, while its tight three-dimensional network structure significantly restore the corrosion resistance of Mg alloy. The wear resistance of N-B-PDMS extremely promotes two orders of magnitude, derived from the high hardness and low friction coefficient of PVA/RGO shell, and further improves the anti-corrosion through this layer-by-layer barrier structure. Owing to the intensive self-healing ability of typical boroxine cross-linked microstructure, artificial damage of B@RGO/PVA coating can be rapidly repaired after 5 min, which surpasses almost the vast majority of previously reported self-healing materials, and therefore the long-term corrosion resistance is almost completely recovered. In this hierarchical microstructure, the top layer and the down layer complement each other to form a multi-functional coating with ultra-fast self-healing and superior corrosion/ wear resistance, which has guiding significance for the design and construction of multifunctional protection coatings for Mg alloy or other metallic materials.