Developing a superplastic forming capability in nanometals

Exceptionally high superplastic ductilities may be achieved in metallic alloys when the microstructure consists of very small and reasonably equiaxed arrays of grains separated by grain boundaries having high angles of misorientation. It is now well established that processing through the application of severe plastic deformation provides the potential for achieving submicrometer or nanometer grain sizes in bulk solids, where these grain sizes are generally significantly lower than those attained using conventional thermomechanical processing. This paper describes the development of a superplastic forming capability in three different aluminum-based alloys by processing using the technique of equal-channel angular pressing (ECAP) in which a material is subjected to a high imposed strain by pressing repetitively through a die. Processing by ECAP can be used to achieve superplastic ductilities in these alloys because precipitates are present within the matrix and they serve to retain the ultrafine grain sizes at elevated temperatures.