Effect of Sn on the Color and Tarnishing of Cu-Mn-Zn Alloys

The effect of Sn on the color and tarnishing of Cu-Mn-Zn alloys is investigated quantitatively. Using the CIE LAB color system, color parameters such as L*, a* and V are selected to describe the surface color of atloys while the color difference (AB*) is used to evaluate the color stability. The results show that with the increase of Sn, the color change of Cu-Mn-Zn alloys is greatly reduced and the corrosion resistance in the synthetic sweat is improved dramatically. However, up to 4.4 wt pct Sn does not change the color of Cu-Mn-Zn alloys much. XPS and AES are employed to analyze the tarnished surface. It is proved that a Sn enriched film is formed and Sn takes the form of Sn oxide. This thin and protective oxide film can prevent alloy from further tarnishing.