Properties of a Lean Silver Alloy After Equal Channel Angular Pressing and Conventional Post-deformation

Silver is a soft, precious metal widely used in electronics, medicine, and in the jewellery sector, due to its exceptional properties such as low electrical resistance, antibacterial behaviour, shiny appearance, and resistance to tarnishing. However, final products are usually made of silver alloys to achieve reasonable hardness and strength needed for these kinds of applications. However, alloying is not always the desirable practice, especially in jewellery, as it can reduce tarnishing and corrosion resistance. Therefore, Severe Plastic Deformation is a promising way to improve the mechanical properties [1]. The copper-free silver alloy of the composition Ag 97.2 wt%, In 1.5 wt%, Ge 1.0 wt%, others 0.3 wt% was developed, cast, and cold-drawn. In order to further improve mechanical properties, room-temperature Equal Channel Angular Pressing (ECAP) along with two-step forging (open-die and impression-die forging) and rolling — as two diverse methods of conventional post-deformation — were performed. In this manner, the original grain size of 130 μm was refined to an ultrafine-grained microstructure with mean grain size of 420 nm. Consequently, the combination of ECAP, two-step forging and rolling resulted in outstanding mechanical properties: tensile yield strength of 491 MPa (+355% compared to the as cold-drawn strength), ultimate tensile strength of 550 MPa (+196%), and Vickers hardness of 167 HV1 (+234%). Furthermore, a much more homogeneous hardness distribution over the whole cross-section of the bars was achieved by ECAP. Contrary to some reports on pure silver [2, 3] both, the microstructure and strength remained thermally stable for at least one year at room temperature as well as for at least 100h and 2h at 100°C and 150°C, respectively. Thus, ECAP is able to effectively increase the mechanical properties of this lean silver alloy which exhibits desirable tarnishing and corrosion resistance.