常温时添加剂对Ce-Mn转化膜的影响

为了提高常温下Ce-Mn转化膜在铝合金表面的成膜速度和耐腐蚀性能,在室温、pH=2的Ce(NO3)3和KMnO4的混合溶液中分别添加H3BO3、Zr(SO4)2、NaF、HF、NaBF4和Na2ZrF66种添加剂,研究添加剂对Ce-Mn转化膜的影响.通过光学显微镜、涡流测厚仪、点滴腐蚀法、Tafel极化曲线和交流阻抗等研究了膜的金相组织、厚度及耐腐蚀性能等;同时,通过SEM和EDS研究了氟化钠对膜的形貌和成分的影响.结果表明:氟化钠是较佳的常温成膜促进剂,常温下9 min就能成膜,相对于无添加剂的Ce-Mn转化膜,膜厚增加2.3倍,耐点滴腐蚀时间延长2.0倍,腐蚀电流密度降低至原来的1/3,膜电阻提高3.9倍:添加NaF后膜的铈含量从5.14%提高到8.59%,锰含量从7.70%提高到14.42%.

Influence of Additives on Ce-Mn Conversion Coating at Room Temperature

This project aims at improving the rate of coating formation and corrosion resistance of Ce-Mn conversion coating on aluminium alloy surface through additives. The additive was H3BO3, Zr(SO4)2, NaF, HF, NaBF4 or Na2ZrF6 , respectively. The behaviours of Ce-Mn conversion coatings formed with different additive were investigated. The metallographic structure and film thickness of the Ce-Mn conversion coating were studied by optical microscope and eddy current thickness meter, respectively. the dripping corrosion-resistant time test, Tafel polarization curves and electrochemical spectroscopy (EIS) were used to investigate the corrosion resistance properties of the Ce-Mn conversion coating formed under the same conditions (i. e. deposition temperature and time, bath pH, concentration of Ce(NO3)3 and KMnO4). The results indicated that NaF was an optimal additive. The Ce-Mn conversion coating was prepared on 6063 aluminium alloy using Ce(NO3)3 , KMnO4 and NaF at the room temperature, 9min and pH=2.0. The results show that the addition of NaF to the treating bath will accelerate the coating formation, could increase the film thickness to 2.3times, the coating anti-corrosion performance to 2.0 times, the impedance value to 3.9 times and the corrosion current density decreased to 2.9 times against that treated without accelerator,respectively. Effect of NaF on micro-morphology and element composition of the coating were analysed with SEM and EDS, the added NaF will change the Ce and Mn content in the coating from 5.14% to 8.59% and from 7.70% to 14.42%, respectively. To rationally interpret the influences of NaF, the mechanism of formed coating was made in this paper.