| This work investigates the possibility of achieving superior ductility at room temperature (RT) in the binary Al-Zn alloys with different content of Zn from 5 to 30 wt.% thanks to the formation of ultrafine-grained (UFG) structures with a grain size below 500 nm by the high pressure torsion (HPT) techniques. The supersaturated solid solutions in investigated Al-Zn alloys decomposed during HPT processing resulting in nucleation and growth of secondary Zn precipitates and/or formation of grain boundary Zn segregations. The studied HPT deformed UFG Al-30Zn alloy demonstrates a ductility of 35%. The maximal elongation-to-failure was reached by applying a strain rate of 104 s-1. The observed strain rate sensitivity values are close to ones typical of superplastic behavior and were usually observed only at high temperatures above 0.5 Tm. The UFG Al-30Zn alloy becomes superductile at RT. At the same time the ductility of UFG Al-5Zn, Al-10Zn alloys was found to be considerably lower and did not exceed 50% at RT. It is suggested that it is the Al-30Zn alloy that contains a volume fraction of Zn-wetted grain boundaries which is sufficient to provide active grain boundary sliding in an UFG material. |
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