CORROSION BEHAVIOR OF COPPER ALLOYS IN DEEP OCEAN ENVIRONMENT OF SOUTH CHINA SEA

The corrosion in deep ocean environment has been paied more and more attentions to the exploitation of marine resources. Different from shallow marine environments, deep ocean environments are specially characterized by high hydrostatic pressure, low temperature, variable dissolved oxygen content and pH value in deep ocean, etc.. So the corrosion behaviour of materials, such as ferrous and nonferrous metal and coatings, in deep ocean environments is different from that in shallow marine environments. A number of researches have been carried out to investigate the corrosion behaviour of metals in natural deep ocean in a few developed countries. Such researches, however, began until 2008 in South China Sea. In this work, the corrosion behavior of 1162 brass, QA19-2 and QSn6.5-0.1 bronze in 800 and 1200 m deep ocean environments of South China Sea was studied using field tests. The results indicated that the corrosion rates of copper alloys decreased in the following order: 1162 (0.042 mm/a) > QSn6.5-0.1 (0.004-0.007 mm/a) > QA19-2 (0.003 mm/a). The corrosion rate of 1162 brass decreased linearly with the increase in depth. While the corrosion rates of QA19-2 and QSn6.5-0.1 bronze decreased first and then increased with the increase in depth. The minimum value of corrosion rate occurred between 800-1200 m. The morphology and composition of corrosion products were investigated using SEM, EDS and XRD. The results demonstrated that the dezincification corrosion obeying solution-redeposition mechanism in 1162 brass occurred. The corrosion products were composed of Cu, ZnO, Zn-5(OH)(8)Cl2H2O and Cu(OH)(2)H2O. And the dealloying corrosion in QA19-2 and QSn6.5-0.1 bronze occurred. The corrosion products of QA19-2 bronze consist of Cu2O and CuCl2, and those of QSn6.5-0.1 bronze Cu2O, CuCl2 and Cu2Cl(OH)(3).