Effects of Indium and Gallium ratio on tarnish resistance, corrosion and mechanical properties of 950 silver alloy

Abstract

The effects of Indium (In) and Gallium (Ga) ratio on tarnish resistance, corrosion and mechanical properties of 950 silver alloy were studied. 950 Silver alloy with aluminium (Al), silica (Si) and germanium (Ge) were added with In and Ga at the range of 0.44 to 1.90 weight percent. The increment of secondary structure with Ge-Si rich phase in Ag-Al alloy increases hardness, but reduces ultimate tensile strength. The addition of In and Ga improves tarnish and corrosion resistance. The color differences as indicated by Delta E tolerances (DE*) of Ag-Al alloys are in the range of 8.64 to 11.40 while this property of Ag-Cu is 39.37. Ecorr of Ag-Al alloys are in the range of -0.068 to -0.010 V which are higher than that of Ag-Cu Alloy (-0.147 V). Besides, Ga is more effective for tarnish and corrosion resistance than In. However, Ga/In co-addition reduces these properties by the formation of Ge-Si-Ga-In phase. The protective thin film of Ag-Al alloy was detected by XPS. The Al2O3, In2O3 and Ga2O3 films were found. When the proportion of Ga in Ag-Al alloys increases, the hardness marginally increases while the tensile strength slightly reduces. The additions of Al, Ga, In, Ge and Si reduce the melting point of Ag-Al alloys comparing with Ag-Cu alloy and simultaneously improve the casting quality.