Effect of pressing routes on the microstructure and strength in equal channel angular pressing of Cu-3.75Ag

Abstract

The combined effects of thermo-mechanical treatment and equal channel angular pressing (ECAP) on the strength and microstructure of Cu-3.75Ag were studied. The strength of Cu-3.75Ag at 1% strain after eight passes of ECAP with two intermediate heat treatments reached 758 MPa and 849 MPa in route A and route Bc respectively. The hardness increased upon heat-treatment in route Bc, in contrast to the drop of the hardness in route A, suggesting that the hardening caused by re-precipitation is more active due to more effective dissolution of second-phase particles in route Bc. The flow stress increased more rapidly with intermediate heat treatments and reached 842 MPa after 8 passes, greater than that (791 MPa) without intermeadiate heat treatment in route Bc. The more rapid increase of strength/hardness and the attainment of higher hardness/strength after intermediate heat treatment are likely to be attributed to the formation of more stable wall structure and rearrangement of solute atoms/precipitates. The spacing between precipitates in Cu-3.75Ag ECAPed for 4 pass in route Bc was measured to be approximately 12.5 nm, which is close to the calculated activated length (12.8 nm). The most probable rate controlling mechanism of Cu-3.75 Ag is suggested to be the interaction between dislocations and precipitates.