Role of the encapsulation strategy of smart containers on corrosion resistance and self-healing performance of micro-arc oxidation coating

Encapsulating smart nano-containers loaded with corrosion inhibitors into coating is a promising approach to functionalize micro-arc oxidation (MAO) coating. The encapsulation strategy of smart containers has a great influence on the microstructure, corrosion resistance and self-healing performance of the smart MAO coating. In order to provide a comprehensive understanding, two kinds of MAO coating encapsulated smart containers (HNT-8HQ), MAO-HNT-8HQ (1S) coating (one-step preparation in an MAO electrolyte containing smart nano-containers) and MAO + HNT-8HQ (2S) coating (pre-prepared MAO coating through an embedding nano-container processing) were prepared on AZ31 magnesium alloy. The incorporated HNT-8HQ in electrolyte can effectively reduce coating porosity and increase coating thickness. Both smart MAO coatings show considerable improvements in the corrosion resistance and a certain self-healing capacity. The post-embedding treated coating (MAO + HNT-8HQ (2S)) has better long-term durability and self-healing performance than one-step preparation coating (MAO-HNT-8HQ (1S)). The low-frequency impedance modulus (|Z|_ƒ=0.01 Hz) of MAO + HNT-8HQ (2S) coating is 1.33 times that of MAO-HNT-8HQ (1S) coating after immersion in 3.5 wt% NaCl solution for 168 h. The MAO + HNT-8HQ (2S) coating has higher impedance values than MAO-HNT-8HQ (1S) coating during the entire self-healing process. The low-frequency impedance modulus of scratched MAO + HNT-8HQ (2S) coating is 3.33 times that of scratch MAO-HNT-8HQ (1S) coating after a 72 h self-healing process.