5383铝合金表面化学镀镍的热力学分析

Thermodynamic Analysis of Electroless Plating Nickel for 5383 Aluminum Alloy

分别采用一次、二次浸锌工艺在5383铸态铝合金表面进行化学镀镍,并对不同镀液pH值和温度下形成的各种镀层进行了扫描电镜(SEM)观察、能谱分析(EDS)、X射线衍射(XRD)物相分析。通过电化学腐蚀实验对镀层在3.5%(质量分数)NaCl溶液的耐蚀性进行测试,采用热力学分析化学镀镍反应机理并研究施镀温度和镀液pH值对镀层的影响。结果表明,二次浸锌后5383铝合金表面的锌含量较一次浸锌更低而镀层更加均匀、致密;化学镀镍中的关键反应步骤为H2→2Had;其中pH值是影响化学镀镍层厚度的主要因素之一并且酸性条件下P的含量比碱性条件下要高许多,Ni-P镀层为非晶相;在pH=4.5、温度90℃环境下化学镀镍所得镀层的耐蚀性能最佳。

Electroless nickel plating was conducted on surface of 5383 cast state aluminum alloy with one time and two times zinc dipping process. Kinds of coatings were investigated with scanning electron microscopy （SEM）, energy dispersive spectroscopy （EDS） analysis and X-ray diffraction （XRD） under the conditions of different pH value and temperature. According to the electrochemical corrosion experiment,the corrosion resistance of coating in 3. 5wt% NaCl solution has been tested. According to thermodynamic analysis of the chemical plating nickel, the influences of the plating bath temperature and pH value to the coating were analyzed. The experimental results indicate that after two times zinc dipping process, the content of zinc became lower and the coating became well-distributed and denser, compared with 5383 aluminum alloy surface of the one time. The key reaction step of electroless nickel plating is H2→2Had. The pH value is the main factor of the thickness of electroless nickel plating. The content of P element under acidic conditions is higher than that under alkaline conditions, and the Ni-P alloy coating is amorphous phase. The corrosion resistance of nickel plating is optimal as the pH value is 4. 5 and temperature is 90 ℃.