30CrMnSiA钢表面镉镀层化学转化膜的电化学特性

Electrochemical Characteristics of Chemical Conversion Film of Cadmium Coating on 30CrMnSiA Steel Surface

目的通过研究镉镀层绿色化学转化膜的电化学性能,获得镉镀层最佳绿色化学钝化工艺。方法采用无氰镀镉工艺,在30CrMnSiA钢表面电镀镉。采用植酸和钼酸钠在镉镀层表面进行绿色钝化处理,构建复合化学转化膜。通过研究钼酸钠浓度、处理时间和植酸浓度对绿色钝化处理镀镉层在质量分数为3.5%的NaCl溶液中电化学性能的影响,获得最佳的镀镉层绿色钝化工艺。结果在处理时间为10 min、植酸的质量分数为1.0%的条件下,当钼酸钠的质量分数增至3%时,开路电压先从−0.7419 V增至−0.7397 V后,再降至−0.7611 V,电荷转移电阻R_(ct)从2.34 kΩ·cm^(2)增至8.79 kΩ·cm^(2),腐蚀抑制率从72.9%增至92.8%,自腐蚀电流密度J_(corr)从81.47μA/cm^(2)降至最低值(6.8872μA/cm^(2))。当钼酸钠和植酸的质量分数分别为2.0%和1.0%时,随着处理时间的延长,开路电压从−0.7559 V增至−0.7295 V,R_(ct)先增至6.68 kΩ·cm^(2),然后降至5.28 kΩ·cm^(2),自腐蚀电流密度从16.26μA/cm^(2)降至4.527μA/cm^(2)。当钼酸钠的质量分数为2.0%、处理时间为10 min时,随着植酸浓度的增加,试样的开路电压从−0.7393 V降至−0.7561 V,R_(ct)先增至6.68 kΩ·cm^(2),然后降低,自腐蚀电流密度J_(corr)呈现先降至最小值后再增大的趋势。结论与镉镀层相比,经化学转化膜处理后试样表现为高的开路电压、大的电荷转移电阻和低的自腐蚀电流。得到了耐蚀性好且成本较低的镉镀层表面绿色钝化工艺,钼酸钠和植酸的质量分数分别为2.0%和1.0%,处理时间为10 min。

The work aims to obtain the best green chemical passivation process of cadmium plating layers by studying the electrochemical properties of green chemical conversion films of cadmium plating layers.The cadmium coatings were electroplated on the surface of 30CrMnSiA steel through the cyanide-free cadmium plating process,and the green passivation treatment was performed on the cadmium coating on the surface of 30CrMnSiA steel in the solution containing phytic acid and sodium molybdate,then a composite chemical conversion film was constructed on the surface of the cadmium layer.After the effects of sodium molybdate concentration,phytic acid concentration and treatment time on the electrochemical properties of the green passivation cadmium plating layer were studied in 3.5wt.%NaCl solution,the green chemical passivation process of cadmium plating layer was obtained.When the treatment time was 10 min and the concentration of phytic acid was 1.0wt.%,with an increase of 3%in the concentration of sodium molybdate,the open circuit voltage value of the sample first increased from−0.7419 V to−0.7397 V,and then decreased to−0.7611 V.And the charge transfer resistance R_(ct)value and corrosion inhibition rate also increased from 2.34 kΩ·cm^(2)to 8.79 kΩ·cm^(2)and 72.9%to 92.8%,respectively,while its self-corrosion current density J_(corr)first decreased from 81.47μA/cm^(2)to 6.887μA/cm^(2).If the concentrations of sodium molybdate and phytic acid were 2.0wt.%and 1.0wt.%,respectively,with the increase of treatment time,the open circuit voltage value of the sample increased from−0.7559 V to−0.7295 V.Its R_(ct)value first increased to 6.68 kΩ·cm^(2),and then decreased to 5.28 kΩ·cm^(2),while its self-corrosion current density decreased from 16.26μA/cm^(2)to 4.527μA/cm^(2).When the concentration of sodium molybdate was 2.0wt.%and the treatment time was 10 min,with the increase of phytic acid concentration,the open circuit voltage value of the sample decreased from−0.7393 V to−0.7561 V.And its R_(ct)value first increased to 6.68 kΩ·cm^(2),and then decreased,while the self-corrosion current density J_(corr)value first decreased to the minimum value and then increased.Compared with the cadmium coating,the samples treated with the chemical conversion coating have higher open circuit voltage,larger charge transfer resistance and lower self-corrosion current.The green passivation process for the surface of cadmium coating has good corrosion resistance and low cost concentration.The sodium molybdate and phytic acid are 2.0wt.%and 1.0wt.%,respectively,and the treatment time is 10 min.