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.
Recent Findings in Superior Strength and Ductility of Ultrafine-Grained Materials