Bi addition increases strength and strain-softening behavior in SAC305

The effects of adding 1–3 wt.% Bi on the mechanical properties of Sn-3.0Ag-0.5Cu lead-free solder at two different effective plastic strains were examined using constant strain rate nanoindentation. Bi additions increased the hardness at a given strain due to solid solution and precipitate strengthening. However, strain-softening behavior corresponded with increases in Bi content; this was attributed to localized deformation arising from microstructural heterogeneity. There was a strong correlation between normalized pile-up height and the strain-hardening exponent derived from indentation hardness. This provides a method for quantifying strain-softening behavior, particularly where conventional bulk testing is challenged by scale.