Influence of rare earth elements on corrosion behavior of Al-brass in marine water

The corrosion behaviors of Al-brass in stagnant and flowing marine water as a function of combinative rare earths (Ce and La) addition were investigated by electrochemical techniques, X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was demonstrated that RE elements could make the corrosion product layer more protective and strengthen the cohesion between the film and matrix in stagnant seawater. The electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) analysis confirmed that a duplex layer, which was mainly composed of an inner Al2O3 with trace amounts of RE compounds and an outer basic chloride of copper or zinc like (Cu, Zn)2Cl(OH)3, Cu(OH)Cl and CuCl2·3Cu(OH)2 layer was formed on RE-contained Al-brass surface and that the inner layer was responsible for the good corrosion resistance of the alloy. While only a porous and non-protective corrosion product layer was formed on the Al-brass alloy without RE addition, which made small values of the corrosion resistance. Additionally, in flowing marine water with velocity about 2 m/s, pitting corrosion occurred on the Al-brass surface and RE addition could availably decrease pitting sensitivity of the alloy.