Influence of Alloy Addition on Properties of Silver Alloys

Abstract

The color, tarnish resistance, hardness and microstructure of silver alloys were studied by using portable UV-vis spectrophotometer, Vickers hardness tester and light microscope, respectively. Two systems of alloys were investigated including Ag-Cu-Si and Ag-Cu-Si-Zn. High percentage of Cu was varied to study color changes of the alloys. Si and Zn were added for tarnish resistance enhancement. Samples were cast at 960 °C by flame torch and then cooled in air. The result shown that color of high Cu-adding alloys was yellow with an investigation by portable UV-vis spectrophotometer. The highest hardness was found in A2 sample, 69.5 wt%Ag-30 wt%Cu-0.5 wt%Si, at 120.60 HV because the composition is near eutectic point. The hardness was slightly decreased after adding Zn in all samples. The microstructure of A1 sample including 74.5 wt%Ag-25 wt%Cu-0.5 wt%Si was similar to sterling silver but its dendrite was shorter than that of sterling silvers. In A2 sample, composition near eutectic point, showed the spheroidal-like shape of phase. Moreover, high content of Cu was found in the matrix phase of this sample. The matrix phase of A3 sample, 49.5 wt%Ag-50 wt%Cu-0.5 wt%Si, was b phase due to a high Cu content (50wt%). All samples added Zn showed a third phase in eutectic-phase area, which will be investigated in future.             Keywords : silver alloys, tarnishing resistance, microstructure, hardness