Investigation on the Corrosion Behavior of Ag-Cu-Al-Y Alloys in Na_2S Solution

The corrosion behaviors of Ag-Cu-Al-Y alloys in Na2S solution were investigated based on the kinetics of corrosion weight loss analysis, the microstructure characterization was analyzed by optical microscope(OM), scanning electron microscope(SEM) and energy diffraction spectrum(EDS). The results indicated that the corrosion resistance of Ag-Cu-Al alloys was improved by the addition of Y, and the best performance was exhibited in the alloy with 0.03at% Y. The sulfuration corrosion of Ag-Cu-Al-Y alloys occurred preferentially at the grain boundaries. A dense protective oxide layer composed of Y2O3 and Al2O3 was formed firstly, which prevents further diffusion of oxygen and sulfur ions. With the external oxide layer peeling off, oxygen and sulfur ions diffused rapidly into the internal alloy and preferentially reacted with Cu to form Cu2S. The corrosion layer was constructed by two layers, an inner layer of dense oxide and a loose outer layer of oxides and sulfides mixture.