Enhanced Strength and Ductility in Hypo-Eutectoid Cu-Al Alloys through ECAP and Annealing

Abstract:

In the present investigation, a bimodal structured alloy with ultrafine-grained (UFG) eutectoid matrix embedded with micrometer-grained pre-eutectoid phase was introduced into the hypo-eutectoid Cu-10.8wt.%Al and Cu-11.3wt.%Al alloys by means of pre-pressing heat-treatment, equal-channel-angular pressing (ECAP) and subsequent annealing. Different size of micrometer grained pre-eutectoid phase was obtained by controlling the cooling rate during pre-pressing heat-treatment of the hypo-eutectoid alloy. The tensile deformation behavior of the developed microstructures is characterized by a maximum tensile yield strength up to 800MPa, which is three times higher than that of the un-treated alloy. It is found that the size of the micrometer grained pre-eutectoid phase is critical to the improvement of the bimodal structured alloy. With larger micrometer grained pre-eutectoid phase, no obvious improvement in plastic elongation was observed with the increase of volume fraction of the pre-eutectoid phase from 20% to 40%, but a decrease in the yield tensile strength was observed. An optimal combination of strength and ductility was obtained particularly in those samples embedded with small-sized micrometer-grained pre-eutectoid phase, which provide extra strain gradient hardening effect.