Corrosion resistance of a magnesium hydroxide/stearic acid composite coating fabricated by vapor diffusion method on Mg-Li-Ca alloy

Abstract

A composite coating of magnesium hydroxide/stearic acid on surface of Mg-1Li-1Ca alloy was prepared using vapor diffusion method to improve the corrosion resistance. The surface morphology and chemical composition of the films were characterized by high resolution scanning electron microscopy (HRSEM), Fourier transform infrared spectrometer (FTIR) and X-ray diffraction analysis (XRD). Electrochemical experiments and immersion test were conducted to study corrosion resistance of the obtained composite coating.The formation and degradation mechanisms of the composite coating were proposed.The results show that the magnesium hydroxide coating has a petal-like structure and is well-adhered to the surface of Mg-1Li-1Ca alloy.The stearic acid coating does not change the petal-like structure of the magnesium hydroxide coating. However, the stearic acid can effectively prevent the aggressive medium penetrating into the internal coating due to its low surface energy and good hydrophobicity.The corrosion current density of the magnesium hydroxide/stearic acid (Mg (OH) 2/SA) composite coating (1.45 × 10–7A/cm2) is decreased by two orders of magnitude compared to that of the Mg-1Li-1Ca alloy substrate (2.70 × 10–5 A/cm2), leading to the enhanced corrosion resistance of magnesium alloy.

Keywords

• magnesium alloy
• corrosion
• layer-by-layer assembly
• vapor diffusion method
• coating