A smart coating for Mg alloys based on mPDA/h-BN hybrids: Achieving self-healing via pH and light dual-responsive behaviour

Despite the outstanding lightweight potential of Mg alloys, their poor corrosion resistance significantly limits their practical applications in engineering. As a more sustainable alternative to solvent-based resins, waterborne polyurethane (WPU) coatings offer notable environmental and safety benefits, including low VOC emissions, non-flammability, and ease of application. However, the inherent microporous defects formed during the curing process, coupled with the absence of self-healing capabilities, notably undermine their protective performance. In this study, a smart hybrid coating was developed to improve the corrosion protection of WPU on Mg alloys. The coating combines benzotriazole (BTA)-loaded mesoporous polydopamine (mPDA) microspheres and hydroxylated boron nitride (OH-BN) within the WPU matrix, achieving active-passive synergistic protection through dual pH/light responsiveness. The mPDA enhances OH-BN dispersion within the matrix and simultaneously acts as an intelligent carrier for the controlled release of BTA under acidic or light-irradiated conditions. Electrochemical impedance spectroscopy (EIS) showed that, after 6 h of immersion in NaCl solution (pH = 3), the damaged composite coating retained an impedance modulus of 2.37 × 10 5  Ω·cm 2 at 0.1 Hz, and maintained a value of 1.97 × 10 5  Ω·cm 2 under light irradiation-28 and 2.8 times higher, respectively, than pure WPU. These results confirm the coating's outstanding corrosion resistance and stimulus-responsive self-healing capability, which arise from the synergistic effects of the OH-BN barrier and BTA release under pH and light stimuli. This work presents a sustainable and intelligent corrosion protection strategy for Mg alloys in harsh environments.