Modification Mechanism of Triethanolamine on Phosphating Coating with High Corrosion Resistance

Abstract—Magnesium alloy has been extensively used in various fields due to prominent physical and chemical properties. Nevertheless, the further application is still impeded by inferior corrosion resistance. Herein, a triethanolamine (TEA)-assisted phosphating coating strategy is presented to protect bare magnesium alloy and specifical optimization effect is investigated in detail. Electrochemical tests demonstrate that the addition of TEA significantly enhances the protective performance of phosphating coating. Further, surface analysis indicates that the modified phosphating coating primarily consisting of CaHPO₄⋅2H₂O is more uniform and denser owing to the excellent crystallinity of CaHPO₄ crystals with the presence of TEA, which can be ascribed to the destructive effect of H₂ bubbles evolution on the deposition of CaHPO₄ crystals and the alleviated compactness of phosphating coating due to the inhibitive effect of TEA on the galvanic corrosion between α-Mg and β-Mg₁₇Al₁₂ phases. This work intensively reveals the modification mechanism of TEA on the corrosion resistance of phosphating coating, and provide a theoretical guidance for screening suitable organic additives.