【作者】 康振华；

【导师】 曾振欧；

【作者基本信息】 华南理工大学 ， 应用化学， 2010， 硕士

【摘要】 铬镀层具有光亮、坚硬、耐磨和耐腐蚀等良好性能，在工业中应用极为广泛。传统镀铬工艺采用的六价铬镀液，对生态环境和人体健康都有严重的危害，目前在电镀工业中受到越来越严格的使用限制。三价铬镀液的毒性低，是最有希望替代六价铬镀液镀铬的工艺。目前研究三价铬镀液镀铬主要有硫酸盐、氯化物和硫酸盐-氯化物三种溶液体系，其中以硫酸盐溶液体系镀铬工艺最为环保。本文主要研究三价铬硫酸盐溶液体系快速镀铬与镀厚铬。通过正交实验和单因素实验研究三价铬硫酸盐溶液体系的最优镀液组成和适宜于快速镀铬与镀厚铬的工艺条件。研究结果表明，三价铬硫酸盐溶液体系的最优镀液组成为：0.5 mol/L Cr³⁺，0.7mol/L HCOOH，60⁸0g/L H₃BO₃，144g/L Na₂SO₄，50g/LK₂SO₄，1.0ml/L润湿剂，pH＝2.50。采用上述镀液组成，在最佳电流密度为10A/dm²和镀液温度为30～40℃的工艺条件下进行快速镀铬，可以得到表面连续致密和均匀光亮的铬镀层，电流效率可达25.0％以上。这种新工艺在铜基体上电镀10s就可得到平均厚度为0.40μm以上的铬镀层，平均镀速可达到2.50μm/min；但在低碳钢基体上铬镀层的平均厚度只有0.10μm，平均镀速只有0.70μm/min。这种新工艺进行长时间连续快速镀铬时，镀液消耗严重、pH值快速下降，需经常维护。采用上述镀液组成在电流密度为8-11A/dm²和镀液温度为30～40℃的工艺条件下可电镀得到性能良好的厚铬镀层。对于平面镀件，在镀液循环流动条件下可获得厚度大于30μm、白亮致密的铬镀层，平均镀速可达到25μm/hr。对于圆柱形镀件，在镀件转动条件（工件转速为20r/min）下可获得厚度大于50μm白亮致密的铬镀层，平均镀速大于20μm/hr。电镀过程中采用阴极保护，在减震器上可获得厚度大于50μm、均匀的白亮铬镀层，平均镀速大于30μm/hr。三价铬硫酸盐溶液体系镀厚铬时，铬镀层的厚度与镀速都随电流密度增大而增加；随温度升高而降低。厚铬镀层的性能测试结果表明：三价铬硫酸盐溶液体系电镀得到铬镀层的平均摩擦系数与六价铬溶液体系电镀得到的铬镀层非常接近；相同条件下的磨损量却远比六价铬溶液体系电镀得到的铬镀层少，其耐磨性能更好。三价铬硫酸盐溶液体系电镀得到铬镀层的显微形貌为结瘤状，硬度随热处理温度升高而增大，原镀态铬镀层的硬度为730HV，在温度为500℃条件下热处理1hr，硬度增加至1090HV。XRD测试和DSC试验对铬镀层进行表征的结果表明：三价铬硫酸盐溶液体系电镀得到的铬镀层（原镀态）在常温为非晶态，在温度为293℃由非晶态转变成晶态。铬镀层（原镀态）经过温度高于293℃的热处理后属于典型的Cr晶型，晶粒大小为纳米级。在高电流密度下电镀得到的烧焦铬镀层也为非晶态，其差别主要是烧焦铬镀层中碳含量较高和含有H、O等其他杂质元素，镀层质量差。更多还原

【Abstract】 Chromium coatings have been widely used in plating industry for its excellent properties ofhardness, corrosion resistance, wear resistance and low coefficient of friction . However, thetraditional hexavalent chromium plating, which does harm to the environment and the human,is restricted more and more in a variety of industries. Consequently, it is very urgent to studyand develop the technics for replacing hexavalent chromium plating such as trivalentchromium plating process, chromium plating process of lower concentration and chromiumalternative process. Among them, trivalent chromium plating process develops quicker and isthe most likely to be the replacement for hexavalent chromium plating process.There always have been three solution systems on trivalent chromium plating, which aresulfate solution, chloride solution and sulfate-chloride solution systems. And the sulfatesolution system is the most friendly to environment. A new trivalent chromiumelectrodeposition process in sulfate system, which was used for high-speed chromium platingand thick chromium plating, had been studied in the paper. By orthogonal experiments andsingle-factor experiments, the optimal compositions of trivalent chromium electrolyte wereobtained as follows: 0.5 mol/L Cr³⁺, 0.7mol/L HCOOH, 60⁸0g/L H₃BO₃, 144g/L Na₂SO₄,50g/L K₂SO₄, 1.0ml/L wetting agent; and with the value of pH at about 2.50. The chromiumcoating which was consecutive and compact was obtained at the optimal current density of10A/dm² and bath temperature of 30⁴0℃, by means of high-speed plating in sulfateelectrolyte above, and the current efficiency of trivalent chromium plating reaches 25.0%and above. The average thickness reaches over 0.40μm on the copper at the current density of10A/dm², after plating 10s, with the average plating rate of 2.50μm/min. However, theaverage thickness on mild steel and nickel is about 0.10μm and the plating rate is only0.70μm/min on the same condition. The bath volume of trivalent chromium plating willdecrease, the pH lower after long-time electroplating.A thick chromium coating could be electroplated on substrates of different shapes intrivalent chromium electrolyte above. The chromium deposit with thickness of 30μm couldbe obtained on planar workpieces by circulation flow method with average plating rate at above 25μm/hr, and the optimal bath temperature was 30 40℃, and current density was 8 10 A/dm². For cylindrical workpiece, above 50μm white and bright chromium coating couldbe deposited by cathode revolver method, and it gained its highest plating rate when thecurrent density was 8¹1A/dm², rotary speed 20r/min and pole distance 8cm. Moreover,above 50μm white chromium could be deposited on shock absorber by cathode-protectingmethod, and the best current density and bath temperature were 15²0A/dm² and 35⁴0℃.The performances of thick chromium deposit obtained as above were tested in the paper,and the result indicated that the average friction coefficient of trivalent chromium was close tothat of hexavalent chromium, and the abrasion loss of trivalent chromium was much less thanthat of hexavalent chromium, so the abrasion performance of trivalent chromium was betterthan that of hexavalent chromium. The deposit hardness of trivalent chromium beforeheat-treatment was 730HV, and increased with increasing the heat treatment temperature andreached 1090 HV at 500℃. The micro morphology of trivalent chromium coating was nodule,and the diameter of nodule became small as the heat-treatment temperature rise. The depositchanged color when the heat-treatment temperature reached 600℃.The crystal structure of trivalent chromium deposit was characterized by XRD test andDSC test, and the result showed that the trivalent chromium coating before heat-treatment wasnon-crystalline, and transformed to crystalline after heat-treatment at 293℃. And thechromium deposit after heat-treatment at 400℃was typical Cr crystalline, with crystallinegrain of nanoscale. The burning chromium deposit at high density current density wasnon-crystalline, which was as same as chromium deposit before heat-treatment. Thedifference between them might be that the carbon content in burning chromium deposit werehigher and there were impurity elements such as H, O and so on in buring deposit, whichworsened deposit quality.更多还原