A smart composite coating with self-reporting and self-healing functions to enhance corrosion protection for magnesium alloys

Smart coatings play crucial roles in realizing excellent corrosion protection on metals and alloys. However, the preparation of smart composite coatings exhibiting self-reporting and self-healing dual function still remains a challenge. Herein, a novel smart composite coating was successfully fabricated by incorporating the ionic liquid grafted carboxylated carbon nanotube and phenolphthalein into a micro-arc oxidation coating (MAO/PP/CCNT-IL) for AZ31B Mg alloy protection. The electrochemical tests including potentiodynamic polarization and electrochemical impedance spectroscopy reveal that the MAO/PP/CCNT-IL composite coating shows the best corrosion protection on the AZ31B Mg substrate among all coatings prepared in this work. In addition, the salt spray experiment in 5 wt% NaCl solution suggests that the occurrence of conspicuous pink within only 12 min can rapidly warn microdamage and microsurface damage, exhibiting a self-reporting effect. Meanwhile, the smart coating also presents outstanding healing property by reacting CCNT-IL with Mg ions from the substrates to generate the chelates to be covered on the damaged area. Such a smart coating offers a feasible strategy for prolonging the service lifetime of Mg alloys through a convenient, economical and effective way with a promising application in the field of material protection.