NH_4HF_2浓度对AZ91D镁合金化学镀镍过程及镀层性能的影响

Effect of Ammonium Hydrogen Fluoride Concentration on Electroless Plating Process of Nickel and Corrosion Resist-ance of the Coating

目前,有关镀液中F-对镁合金化学镀镍影响的研究还不系统。探讨了AZ91D镁合金化学镀镍液中NH4HF2浓度对化学镀镍初始沉积、镀液缓冲力和镀层的沉积速率、结合力、形貌、耐蚀性的影响。结果表明:F-对镀镍初始沉积有较大影响,若镀液中无NH4HF2时,AZ91D镁合金化学镀镍将难以进行,如果先在含F-的镀液中施镀适当时间后,再放入无F-镀液中施镀,镀镍能顺利进行;随着镀液中NH4HF2浓度的增加,镀液的缓冲性能越来越好,镀层的结合力先增强后减弱,镀层沉积速率和腐蚀速率先减小后增大,镀层胞状物先变小后变大,镀层致密性先变好后变差;当镀液中加入20 g/L NH4HF2时,镀层综合性能最好。

With a view to the lack of systematic study about the effect of F-in plating bath on electroless Ni plating of AZ91D alloy substrate,the effect of concentration of NH4HF2 in electroless Ni plating bath on the initial deposition of Ni,the buffer capacity of the plating bath,and the properties( deposition rate,bonding strength to substrate, morphology,and corrosion resistance) of as-plated Ni coating was investigated. It was found that F-had significant influence on the initial deposition of Ni. When no NH4HF2 was added in the plating bath,it was infeasible to conduct electroless Ni plating of the Mg alloy. Differing from the abovementioned,electroless Ni plating could be well conducted after Mg substrate was pre-plated for a proper duration in the bath containing F-and then plated in the plating bath without F-. Besides,the buffer capacity of the plating bath rose with increasing concentration of NH4HF2,and the bonding strength of the Ni coating to Mg alloy substrate initially rose but declined later with elevating NH4HF2 concentration in the plating bath. In the meantime,the deposition rate and corrosion rate of Ni coating initially declined but rose later with increasing NH4HF2 concentration in the plating bath,the size of the cell-like species in the Ni coating initially rose and then declined slightly therewith,and the compactness of the Ni coating rose initially but declined later therewith. Particularly,the electroless Ni coating obtained from the plating bath containing 20 g / L NH4HF2 had the best comprehensive properties.