硫酸盐体系三价铬电沉积厚铬工艺研究

Research on process of trivalent chromium electrodeposition of thick chrome coatings from sulfate system

以较为环保的硫酸盐体系进行三价铬电镀，研究了甲酸钠、羧酸和硫酸铵质量浓度以及镀液pH、温度、电流密度和电沉积时间对铬镀层厚度和光亮范围的影响，通过扫描电镜和x射线衍射对镀层结构进行了表征。得出了三价铬电沉积厚铬的较佳工艺条件为：硫酸铬90g／L，甲酸钠30g／L，羧酸21g／L，硫酸铵10g／L，pH2．0，温度50℃，电流密度20A／dm2，时间30～60min。在以上条件下电沉积铬，镀层厚度可达15．26～22．51μm，持续电镀能力为53A·h／L。铬镀层微观形貌为胞状凸起，经过热处理后该胞状凸起消失并出现微裂纹，而且热处理后镀层由非晶态转变为晶态。

Trivalent chromium electroplating was carried out using an environmentally friendly sulfate system. The effects of mass concentrations of sodium formate, carboxylic acid and ammonium sulfate as well as bath pH, temperature, current density, and electrodeposition time on the thickness and brightness area of chromium deposit were studied. The microstructure of chromium deposit was characterized by scanning electron microscopy and X-ray diffraction. The optimal process conditions for trivalent chromium electrodeposition of thick chromium coating were obtained as follows： chromium sulfate 90 g/L, sodium formate 30 g/L, carboxylic acid 21 g/L, ammonium sulfate 10 g/L, pH 2.0, temperature 50 ℃, current density 20 A/dm2, and time 30-60 min. The chromium deposit with a thickness of15.26-22.51 μm was obtained under the above conditions, and the continuous plating capacity of the bath is 53 A.h/L. The micromorphology of the as-prepared chromium deposit presents many cell-like protrusions. The structure of the deposit is changed from amorphous to crystal structure after heat treatment, and the cell-like protrusions disappear while micro-cracks appear.