Fe^(3+)对钢铁表面氟铁酸盐转化膜的改性作用

Effect of Fe^(3+) on Corrosion Resistance of Fluoferrite Conversion Coating on Iron and Steel

为了提高钢铁表面氟铁酸钾转化膜的耐蚀性,在以KF为主成膜剂的转化液中加入FeCl3进行改性,在A3钢表面制备了新型的氟铁酸盐转化膜。通过SEM、EDS及Tafel曲线研究了Fe3+浓度对氟铁酸盐转化膜耐蚀性能的影响,并优化了转化膜制备工艺条件。结果表明:钢铁表面改进型氟铁酸盐转化膜的最佳制备工艺为50 g/L KF,20 mL/L HNO3,15 g/L(NH4)2S2O8,2.0 g/L FeCl3,pH值2.0,时间1.5 h,温度27~30℃;与转化液中未加FeCl3相比,最优工艺所得氟铁酸盐转化膜更加致密,其自腐蚀电位正移了约116 mV,自腐蚀电流密度下降了约86%,耐中性盐雾腐蚀时间增加了5倍以上,耐蚀性显著提高,且转化膜与钢铁基体结合较好。

FeCl3 was introduced into the conversion fluid containing KF as the major film-formation agent to prepare a novel fluoferrite conversion coating with improved corrosion resistance on the surface of A3 steel.The effect of Fe3+ concentration on the corrosion resistance of the fluoferrite conversion coating was investigated based on scanning electron microscopic observation,energy dispersive spectrometric analysis,and Tafel curve measurement,and the condition for preparing fluoferrite conversion coating was optimized.It was suggested that the conversion fluid for preparing title conversion coating consisted of 50 g/L KF,20 mL/L HNO3,15 g/L(NH4)2S2O8,and 2.0 g/L FeCl3,while the conversion should be conducted at a pH value of 2.0 and a temperature of 27~30 ℃ for a duration of 1.5 h.The conversion coating obtained with the conversion fluid containing FeCl3 under the optimized condition was more compact than the conversion coating obtained in the conversion fluid without FeCl3.Moreover,its self-corrosion potential rose by about 116 mV,and corrosion current density declined by about 86%,showing greatly improved corrosion resistance.Furthermore,the novel fluoferrite conversion coating had good adhesion to the steel substrate.