镀液pH值对镁合金Ni-P化学镀层的影响

Effect of pH Value of Plating Solution on the Performance of Electroless Ni-P Coating on Magnesium Alloy

为了提高镁合金耐腐蚀性能,在AZ61镁合金表面制备Ni-P化学镀层。采用磷酸酸洗对镁合金表面前处理后,在酸性镀液中制备了Ni-P化学镀层,通过SEM、EDAX、XRD及动电位极化曲线、交流阻抗等方法,分析了镀液p H值对Ni-P镀层形貌、成分、厚度、结合力、结构和耐蚀性的影响。试验结果表明:随着镀液p H值升高,组成镀层的细胞状物尺寸逐渐减小,镀层的沉积速度加快,镀层中的磷含量逐渐降低,镀层中的镍含量逐渐上升,镀层的晶化程度逐渐提高。镀层的耐蚀性能则随着镀液pH值的上升先升高,后下降。p H=6.0条件下制备的Ni-P镀层在质量分数为3.5%NaCl溶液中的交流阻抗膜值最高,且自腐蚀电流密度最低,耐蚀性能最好,并根据试验结果分析了镀液pH值对Ni-P镀层耐蚀性能的影响机制。

The work aimed to improve the corrosion resistance of magnesium alloy by preparing electroless Ni-P coating on AZ61 magnesium alloy. The Ni-P coating was electroless-deposited on AZ61 magnesium alloy after pickled by phosphoric acid. Effect of p H value of plating solution on coating morphology,compostion,thickness,binding force,structure and corrosion resistance of the Ni-P coating was studied by scanning electron microsocopy( SEM),energy dispersion analyzer of X-ray( EDAX),X-ray diffractometer( XRD) and electrochemical test.Results showed that the Ni-P layer was in cellular structure,and the size of the structure and the content of P in the layer decreased,while the deposition rate,the content of Ni and the crystallinity of the coating increased with the increase of p H value of the plating solution.Furthermore,the corrosion resistance of Ni-P layer increased first,and then decreased when the p H value increased. When the p H value of the plating solution was about 6.0,the Ni-P layer had the maximum AC impedance value and the lowest corrosion current density,presenting the best corrosion resistance in 3.5% Na Cl solution. Based on experimental results,the influence mechanism of p H value of plating solution on corrosion resistance of Ni-P coating was discussed.