二次浸锌预处理对钛合金化学镀镍沉积行为和镀层结合力的影响

Effect of secondary zinc dipping as a pretreatment on electroless deposition behavior of nickel on titanium alloy and adhesion of the coating obtained thereon

通过电化学测试和扫描电镜分析,研究了钛合金在二次浸锌过程中的电位变化规律及锌层形成过程,并考察了二次浸锌对碱性化学镀镍初期沉积行为的影响,探讨了二次浸锌改善镀层结合力的基本原理。结果表明,钛合金在一次浸锌过程中经历了氧化膜溶解、薄锌层生长及锌层生长-溶解动态平衡三个阶段,表面形成了稀疏的晶须状锌层;二次浸锌的总体规律与一次浸锌类似,但锌层很快达到生长-溶解动态平衡,形成的锌层更均匀、致密,覆盖度更高。二次浸锌有利于后续化学镀镍快速形成完整、均匀的镀层,以及提高钛合金基体与镍镀层之间的结合力。

The variation law of potential and the formation process of zinc layer during the first and secondary zinc dipping were analyzed by electrochemical measurement and scanning electron microscopy. The effect of secondary zinc dipping on initial deposition behavior during alkaline electroless nickel plating was studied. The basic mechanism for secondary zinc dipping in improving the adhesion of nickel coating obtained subsequently was discussed. The results showed that titanium alloy underwent three stages during the first zinc dipping i.e. the dissolution of oxide film, the growth of thin zinc layer, and the dynamic balancing between the growth and dissolution of zinc layer, and a loose whisker-like zinc layer was formed. The general rule for film formation during the secondary zinc dipping was similar to that of the first zinc dipping, but it took less time to reach the dynamic growth-dissolution balance, and the zinc layer formed thereafter was more uniform and compact with a higher coverage. Secondary zinc dipping not only facilitates the quick formation of a complete and uniform nickel coating for the subsequent electroless nickel plating, but also improves the adhesion between titanium alloy and nickel coating.