The role of stacking-fault energy in deformation twinning and work hardening was systematically studied in Cu (78mJ/m2) and a series of Cu-Al solid-solution alloys (0.2, 2, 4 and 6wt%Al with stacking-fault energies of 75, 25, 13 and 6mJ/m2, respectively). The materials were deformed under quasi-static compression at strain-rates of 1000/s in a Split-Hopkinson pressure bar. The quasi-static flow curves of annealed 0.2 and 2wt%Al alloys were found to be representative of solid-solution strengthening and were well described by the Hall-Petch relationship. The quasi-static flow curves of annealed 4 and 6wt%Al alloys exhibited additional strengthening at strains greater than 0.10. This additional strengthening was attributed to deformation twins and to the presence of twins, as confirmed by optical microscopy. The strengthening contribution of deformation twins was incorporated into a modified Hall-Petch equation (using the inter-twin spacing as the effective grain size). The calculated strength was in agreement with observed quasi-static flow stresses. The work-hardening rate of the low stacking-fault energy Cu-Al alloys was independent of the strain rate. The work-hardening rate of Cu and the high stacking-fault energy Cu-Al alloys (low Al content) increased with increasing strain rate.

The Influence of Stacking Fault Energy on the Mechanical Behavior of Cu and Cu-Al Alloys: Deformation Twinning, Work Hardening, and Dynamic Recovery. A.Rohatgi, K.S.Vecchio, G.T.Gray: Metallurgical and Materials Transactions A, 2001, 32[1], 135-44