Corrosion evaluation of artificially aged 6 wt-% tin bronze

This study concerns the corrosion behaviour of wrought 94 wt-%Cu-6 wt-%Sn (B6) bronze, whose composition is similar to materials used for outdoor bronze artefacts. In order to investigate the influence of the composition and microstructure on bronze corrosion processes, electrochemical ac and dc measurements in synthetic acid rain and chloride solutions were performed on the B6 binary alloy in comparison with an as cast bronze having a different degree of purity. Moreover, to perform thin layer activation (TLA) measurements of thickness loss, a suitable radio nuclide 65Zn (t1/2= 244 days) was produced on B6 specimens by a high energy proton beam. Artificial weathering experiments have been carried out by exposing activated and non-activated B6 specimens: To selected pollutants including NOx and SO2 at different concentrations to simulate urban and industrial atmospheres; in a cyclic salt spray cabinet to investigate the effects of marine environments; to basic (NH4)2SO4 solutions reproducing the aggressiveness of ammonia containing wet deposits. At the end of each test, the B6 corrosion rates obtained by weight loss determinations have been compared with those arising from the TLA method. Finally, the nature and microstructure of the surface oxidation products were investigated.