Stress corrosion cracking properties of environmentally friendly unleaded brasses contaning bismuth in Mattson's solution

The purpose of the present investigation was to study the stress corrosion cracking (SCC) properties of environmentally friendly Bi-brasses in Mattsson's solution (0.05 M copper sulfate and 0.5 M ammonium sulfate, pH 7.4) at room temperature. Three unleaded brasses with Bi content ranging from 1 to 3 wt.% and a conventional leaded brass for comparison were investigated. The effect of Bi on SCC of unleaded brasses was studied through polarization test, electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and slow strain rate tests (SSRT). Potentiodynamic polarization studies indicated that the corrosion resistance of Bi-containing brasses was improved as the content of Bi, which shown passivating characteristic in Mattsson's solution, increased. The Pb- and Bi-containing brasses presented an inductive behavior on impedance data in low frequency region at the open-circuit potential (OCP). Such behavior could be attributed to the adsorption process on the alloy surface. The observed dezincified layers after SSRT should be particularly good initiators of SCC as they could induce tensile stress. As the content of Bi increased, the thickness of dezincified layer and the volume fraction of preferentially attacked phase decreased, therefore, SCC resistance of the Bi-containing brasses was improved.