Developing Superplastic Ductilities in Ultrafine-Grained Metals

Conventional superplasticity is generally achieved in metals having grain sizes in the range of ∼2 to 5 μm, but processing by equal-channel angular pressing (ECAP) provides the opportunity of introducing exceptional grain refinement and producing materials with ultrafine grain sizes in the submicrometer range. These materials have the potential for exhibiting excellent superplastic properties when tested in tension at elevated temperatures and examples are presented for representative aluminum and magnesium alloys. When these ultrafine-grained materials deform in superplasticity, internal cavities develop as in conventional superplastic alloys. An example is presented for an aluminum-based alloy, and it is shown that the cavity growth processes are also similar to those in conventional alloys. This article is based on a presentation made in the symposium entitled “Ultrafine-Grained Materials: From Basics to Application”, which occurred September 25–27, 2006, in Kloster Irsee, Germany.