Ductility and formability of ultrafine-grained 5754 aluminium alloy under various strain rates and temperatures

The paper discusses the formability and ductility, under various strain rates and temperatures, of ultrafine grained plates of commercial 5754 aluminium alloy processed by a hybrid process combining multi-turn Equal Channel Angular Pressing and upset forging. The proposed process offers a simple way to produce UFG sheets that are characterized by high formability at elevated temperatures. It was proven that a proper selection of temperature and strain rate makes it possible to obtain elongations in tensile tests exceeding 80%, as well as a two-fold increase in formability, expressed as an increase in the cup height value in a cupping test of a UFG sheet compared with room temperature. This increase in ductility was attributed to enhanced strain rate sensitivity, since the m value exceeds 0.2, indicating a change in the deformation mechanisms at work. Based on apparent activation volume, which was equal to 13 b3, the nucleation and propagation of dislocations through grain and diffusion processes are indicated as the operating deformation mechanisms.