ABSTRACT

Ni-W-P ternary coating was synthesised on AZ91D magnesium alloy substrates by an integrated method. The corrosion resistance mechanism of conversion film-electroless Ni-W-P coatings on a substrate has been examined. Results revealed that the corrosion resistance of Ni-W-P coating with a phytic acid conversion film was better than that with a stannate film. The surface morphologies of Ni-W-P coatings were of an amorphous cellular structure, uniform and dense. Moreover, it was observed that the corrosion rate of Ni-W-P coating with a phytic acid conversion film heat-treated at 200°C reached the minimum of 0.0345 g m⁻²·h⁻¹, the self-corrosion potential was −0.335 V, and the capacitive arc radius from electrochemical impedance spectroscopy testing was the largest, which revealed that the corrosion resistance of these Ni-W-P coatings was the best. The results were ascribed to the formation of a stable chelate on the substrates after phytic acid pretreatment, which improved the bonding strength between the Ni-W-P coatings and substrates.

摘要

采用集成方法在AZ91D镁合金基体上合成Ni-WP三元涂层。研究了基体上转化膜-化学镀Ni-WP涂层的耐腐蚀性能机制。结果表明，带有植酸转化膜的 Ni-WP 涂层的耐腐蚀性能优于带有锡酸盐膜的 Ni-WP 涂层。Ni-WP涂层的表面形貌为非晶胞结构，均匀致密。此外，观察到在 200°C 热处理的具有植酸转化膜的 Ni-WP 涂层的腐蚀速率达到最小值 0.0345 gm ^-2 ·h ^-1，自腐蚀电位为-0.335 V，电化学阻抗谱测试的电容弧半径最大，表明这些Ni-WP涂层的耐腐蚀性能最好。结果归因于植酸预处理后在基材上形成稳定的螯合物，提高了Ni-WP涂层与基材之间的结合强度。