Microstructural homogeneity and superplastic behavior in an aluminum–copper eutectic alloy processed by high-pressure torsion

Abstract

An Al–33 % Cu eutectic alloy was processed by high-pressure torsion (HPT) at room temperature under a compressive pressure of 6.0 GPa for different revolutions up to 10 turns. The Vickers microhardness and microstructure were investigated on vertical cross sections of the disks to evaluate the evolution toward homogeneity with increasing numbers of HPT turns. The hardness behavior follows the strain hardening model of materials after HPT processing and the microstructural development confirms that there is essentially a compatibility between hardness and microstructure in the Al–Cu alloy when processing by HPT. The tensile properties were examined at a high temperature of 723 K after 5 and 10 turns of HPT using a series of strain rates from 3.3 × 10⁻⁵ to 1.0 × 10⁻¹ s⁻¹. Excellent superplastic ductilities were achieved when testing at strain rates below 1.0 × 10⁻³ s⁻¹ with a highest elongation of ~1220 % after 10 turns at an initial strain rate of 1.0 × 10⁻⁴ s⁻¹. Close inspection showed that the optimal superplastic strain rates are displaced to a faster strain rate with increasing revolutions from 5 to 10 turns. A deformation mechanism map was constructed for a testing temperature of 723 K using a combination of theoretical relationships and earlier experimental data reported for a conventional coarse-grained Al–33 % Cu alloy. Inspection shows that this map is in excellent agreement with the experimental data for the ultrafine-grained Al–33 % Cu alloy after processing by HPT.