Effect of Solution Heat Treatment Temperature on Work Hardening and Aging Behavior of Cu–Ni–Si-Co–Cr–Sn Alloy

This study investigated the effect of solution heat-treatment temperature on the work-hardening and aging behavior of Cu–Ni–Si-Co–Cr–Sn alloy for lead-frame and connector applications requiring both high strength and high electrical conductivity. The alloy was solution heat-treated at 830 and 930 °C, cold-rolled under uniform and non-uniform deformation conditions, and subsequently aged to evaluate its mechanical properties and microstructural evolution. The specimen solution heat-treated at 830 °C showed relatively limited hardness increases during both cold rolling and subsequent aging. This behavior was attributed to the low solubility at the lower solution heat-treatment temperature, which left a large amount of residual inclusions in the matrix and reduced the concentration of solute atoms, thereby reducing the work-hardening response during subsequent cold rolling. In addition, during aging, coarse particles were preferentially observed near pre-existing inclusions and grain boundaries, reducing the efficiency of fine precipitation strengthening. In contrast, the specimen solution heat-treated at 930 °C exhibited a greater hardness increase during cold rolling and a much stronger age-hardening response. This was because the higher solution heat-treatment temperature promoted the dissolution of residual inclusions and increased the solute concentration in the matrix, thereby improving the work-hardening capability. Furthermore, the increased dislocation density introduced by cold rolling may have accelerated solute transport along dislocation structures during aging, thereby promoting more effective fine precipitation. These results demonstrate that high-temperature solution heat treatment is effective in achieving a superior combination of strength and electrical conductivity in Cu–Ni–Si-Co–Cr–Sn alloy through subsequent rolling and aging treatments.