High strength and ductile ultrafine-grained Cu-Ag alloy through bimodal grain size, dislocation density and solute distribution

Ultrafine-grained materials produced by different severe plastic deformation methods show very high strengths but their tensile ductility is often very low. In the present work, we demonstrate an approach for retaining high strength while recovering ductility in a Cu-3 at.% Ag alloy through cold rolling and short-time annealing. X-ray line profile analysis of cold-rolled and annealed samples reveals the development of a heterogeneous solute atom distribution due to the dissolution of nanosized Ag particles in some regions of the matrix. In regions with higher solute (Ag) content, the high dislocation density present following rolling is stabilized, while in other volumes the dislocation density is decreased. High-resolution scanning electron microscopy confirms the presence of regions of varying Ag content in the matrix. Microstructure analysis of the rolled and annealed samples revealed bimodal grain size, dislocation density and solute Ag distributions as well as nanosized Ag precipitation. The as-rolled samples exhibit high tensile strengths of ?600-700 MPa with negligible uniform elongation (?1%). After short-time annealing the strength decreases only slightly to ?550-620 MPa with significant improvement in uniform elongation (from 1 to 10%); this is mainly attributed to the bimodal microstructure. � 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.