Revealing the deformation mechanisms of Cu–Al alloys with high strength and good ductility

Abstract

Fully recrystallized Cu-4 at.%Al alloy and Cu-11 at.%Al alloy with grain sizes ranging from 0.5 μm to 80 μm were fabricated by cold rolling and annealing. Tensile tests showed that yield strength, ultimate tensile strength and uniform elongation of the two Cu–Al alloys had linear relationships with the inverse square root of the grain size, and both the tensile strength and uniform elongation were ameliorated with decreasing the stacking fault energy. The strain-hardening curves of the Cu-4 at.%Al alloy shifted slightly with increasing the grain size, but the strain-hardening curves of the Cu-11 at.%Al alloy were very sensitive to the grain size. Microstructures of both alloys deformed to different tensile strains showed that the Cu-4 at.%Al alloy was favored by dislocation slip; in contrast, dislocation slip, stacking faults and deformation twins were widely observed in the Cu-11 at.%Al alloy, and their roles changed at different strain levels in the specimens with different grain sizes. Finally, mechanisms of achieving high strength and ductility in low-SFE materials were analyzed based on the strain-hardening behavior and deformation patterns. Optimal grain size ranges of 0.2–1 μm for the Cu-4 at.%Al alloy and 1–3 μm for the Cu-11 at.%Al alloy were proposed to achieve superior comprehensive mechanical properties.