Designing a robust silane/polyaniline/Ni tri-layer coating for superior corrosion resistance of AZ91 magnesium alloy

Magnesium alloys, particularly AZ91, are widely used in industries such as aerospace, automotive, and electronics due to their lightweight and high-strength properties. However, their susceptibility to corrosion limits their application in harsh environments. This study presents the development of a novel tri-layer coating composed of nickel (Ni), polyaniline (PANI), and a silane-based sol-gel layer to enhance the corrosion resistance of AZ91 magnesium alloy. The Ni layer provides a robust foundation, while the PANI coating, with its coral-like porous structure, improves adhesion and corrosion resistance. The top silane layer, formed from tetraethylorthosilicate (TEOS) and vinyltriethoxysilane (VTES) by a sol-gel method, offers a smooth, hydrophobic surface that significantly enhances corrosion protection. A range of characterization techniques, including field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR), were applied to analyze the microstructure, surface morphology, and chemical composition of the coatings. The electrochemical performance of the coating was evaluated through electrochemical impedance spectroscopy (EIS) in a 3.5% NaCl solution, revealing a remarkable enhancement in corrosion resistance (86.9 kΩ cm2) compared to bare Mg alloy (0.2 kΩ cm2). Notably, the coating exhibited a corrosion resistance of 12.1 kΩ cm2 after 168 h of exposure, still much higher than that of bare Mg, highlighting its long-term protective capacity. The synergistic effects of the Ni, PANI, and silane components were found to be crucial in improving the overall resistance to corrosion. This tri-layer coating presents a promising solution for enhancing the longevity and performance of magnesium alloys in industrial applications.