Exploration of microstructure and surface composition on corrosion initiation of a Cu-Al-Zn alloy

摘要

The aim of this study is to explore the chloride-induced corrosion initiation of a Cu-Al-Zn alloy with composition 89% Cu, 5% Al 5% Zn and 1% Sn (by weight) frequently used as cladding material in modem architecture. Important reasons for the high corrosion resistance of this single-phase alloy in many atmospheric environments is its intrinsic structural homogeneity and spontaneous formation of a thin alumina (Al_2O_3-layer and of a hydrozincite (Zn_5(CO_3)_2(OH)_6)-layer, two complementary acting corrosion barriers within the patina formed. The bulk and surface of the Cu-Al-Zn alloy were analysed by three independent analytical techniques providing information on grain orientation of the microstructure (electron backscatter diffraction, EBSD), lateral distribution of surface chemical composition (scanning Auger electron spectroscopy, SAES) and local variations in Volta potential (scanning Kelvin probe force microscopy mapping, SKPFM). This approach enables the exploration of the effect of microstructure and lateral surface chemical composition on corrosion initiation, and how these alloy parameters influence the variation in relative nobility along the surface, expressed by the Volta potential. An influence of grain orientation could be observed on corrosion initiation, while the chemical composition is quite homogeneous along the surface with no significant effect on corrosion initiation observed.