采用低浓度镀液对深槽带钩的细薄零件电镀硬铬

Hard chromium electroplating for a thin part with deep groove and hook in a low concentration bath

通过低浓度硬铬电镀来改善细薄深槽零件（经编机针）的耐磨性，镀液组成和工艺条件为：Cr03180g／L，浓硫酸1．0g／L，稀土添加剂I1．0g／L，稀土添加剂II2．0g／L，Cr3＋2．0g／L，温度30～50℃，电流密度30～50Mdm2，时间10～20min，阳极为铅锑板。采用超景深显微镜、扫描电镜（SEM）、能谱仪（EDS）、显微硬度计、X射线衍射仪（XRD）和摩擦磨损试验机考察了深槽内壁和表面镀层的外观质量、微观形貌、元素组成、显微硬度、相结构和耐磨性。该工艺可以解决深槽内壁处镀不上铬的难题，所得镀层为纯金属铬，外观光亮、平滑，显微硬度约为730HV，与基体结合良好，耐磨性相对于基体也有所提高。

Hard chromium electroplating was conducted in a low concentration bath to improve the wear resistance of tricot machine needle （a thin part with deep groove）. The bath composition and process conditions are as follows： CrO3 180 g/L, concentrated sulfuric acid 1.0 g/L, rare earth additive I 1.0 g/L, rare earth additive II 2.0 g/L, Cr3＋ 2.0 g/L, temperature 30-50 ℃, current density 30-50 A/dm2, time 10-20 min, and lead-antimony plate as anode. The appearance quality, microscopic morphology, elemental composition, microhardness, phase structure and wear resistance of the chromium coating on the inner wall and surface of deep groove were studied using large depth-of-field metallographic microscope, scanning electron microscope （SEM）, energy-dispersive spectrometer （EDS）, microhardness tester, X-ray diffractometer （XRD） and friction wear tester. The problem that chromium is difficult to be electroplated on the inner wall of deep groove is solved. The coating obtained is composed of pure metallic chromium with a bright and smooth surface, and features a microhardness of ca.730 HV, a good adhesion to substrate, and a better wear resistance as compared with the substrate.