Effect of added Ag on plasticity enhancement of Au80Sn20 eutectic alloys

Abstract

Abstract Inherent brittleness greatly limits machining and applications of Au80Sn20 eutectic solder alloys. To overcome the frangibility of Au80Sn20 eutectic alloys, Ag was added to form novel Au78.44Sn19.6Ag1.96 alloy. The effects of 2 wt% Ag addition on the solidification microstructure and plastic deformation of Au80Sn20 eutectic alloys were then studied. The as-obtained Au78.44Sn19.6Ag1.96 exhibited excellent plastic deformation at room temperature. Ag was well-solubilized in Au5Sn phase to yield (Au,Ag)5Sn, eliminating secondary phase defects in Au5Sn. The point defects introduced by Ag reduced its stacking fault energy and enabled (Au,Ag)5Sn to initiate stacking faults and twinning. Moreover, the typical eutectic growth state of Au80Sn20 alloy was changed. AuSn phase in Au78.44Sn19.6Ag1.96 alloys showed preferential orientation in basal direction, leading to formation of basal-prismatic facets and providing basal slip at room temperature. The ability to coordinate deformation between both phases improved and room temperature plastic deformation reached above 60%. These findings can help steer possible future research regarding the deformation mechanism of fragile metals and provide practical guidance to increase the plasticity of fragile metals for solder manufacturing.