LC4铝合金在氯化钠溶液中的孔蚀特征

Features of electrochemical noise during pitting corrosion of LC4 aluminum alloy in 2.0% NaCl solution

LC4铝合金在 2 .0 %NaCl溶液中发生局部腐蚀的过程中 ,电位噪声的谱功率密度 (SPD)曲线具有相同的特征 ,即在极低频下为白噪声 ,随着频率的升高逐渐转化为 1/fa 噪声 ,相应于一个噪声信号波 ,有一个腐蚀孔出现。在孔蚀诱导期 ,白噪声水平升高 ,截止频率增大 ,SPD曲线的倾斜段直线斜率小于 - 2 5dBv/Hz ,且趋于增大。孔蚀发生后 ,上述 3个参量则各自朝着上述方向的逆方向变化。实验发现 ,孔蚀参数SE 和SG 可以正确的表征孔蚀的发生、发展及材料的均匀腐蚀。阻抗测量结果表明 :孔电阻在刚开始浸泡时较大 ,随后减少渐趋于平稳 ,最后孔电阻又升高。这是因为随着浸泡时间的增加 ,孔面积渐渐增大 ,浸泡 6 5 0 0 0min时 ,孔电阻有所上升 ,可能是由于母孔内子孔的形成所致。产物电阻逐渐稳定上升 ,表明腐蚀产物逐渐增多。

The features of electrochemical noise (EN) of super strength LC4 aluminum alloy in 2.0% NaCl solution during pitting corrosion were investigated. The results show that all the ENs observed are low frequency noises and the white noise( P w) which is independent of frequency in the super low frequency domain and changes to the 1/f a noise with the increasing of frequency. Each pit on the surface of corroding electrode corresponds to sudden jump of electrode potential in time domain. During induced duration of pitting corrosion, the level of white noise and the value of cut off frequency ( f c) increase with the increase of immersion time, while the absolute value of slope of SPD curve's linear part decreases. On the other hand, the above three parameters change in the opposite direction after a pot or a series pits are formed. Based on the EIS displays of LC4 aluminum alloy at various immersion time, one kinds of equivalent were proposed as their physical models. The relation between impedance characteristics and structure and properties of oxide film were discussed.