Contact materials are widely used as electrical parts. Ag-Cd alloy has a good wear resistance and stable contact resistance. But
the Cd exists as coarse oxide in alloy so it have an effect on mechanical properties badly. Moreover, the Cd is an injury material to
environment. Nowadays, the use of Cd is strictly restricted. Because of these disadvantage, Ag-Sn-In alloy has been developed. In
Ag-Sn-In alloy, the Sn : In ratio affects the internal oxidation properties, such as the formation of the oxide layer on the surface. In
this work, we changed and optimized the Sn : In ratio variety for good internal oxidation properties. We have shown that a internal
oxidation process did not fully completed when the Sn : In ratio is over 4 : 1 because of the Sn oxide layer at surface. The increase
of In decelerates the formation of Sn oxide layer.