Strain Hardening, Strain Softening and the Portevin-Le Chatelier Effect in Cryomilled, Ultrafine Grained AA 5083

Abstract

Aluminum alloys consolidated from cryomilled (ball milled in a cryogenic liquid nitrogen or liquid argon slurry) precursor powders show promising increases in strength, commonly >30% over conventionally processed alloys, and acceptable levels of tensile ductility, typically 3-15 %. Mechanical behavior is governed by the microstructural features dependent on the alloy and thermomechanical processing (TMP) route chosen for primary, secondary and tertiary forming. In an effort to improve understanding of the alloying and processing parameters influencing mechanical behavior, numerous studies have been performed with various Al-Mg compositions and TMP routes. Here we focus on cryomilled and consolidated AA 5083 to characterize differences in the tensile stress-strain behavior specific to strain hardening, strain softening and Portevin-Le Chatelier (PLC) effects that have been observed. Using stress-strain data from multiple investigations, the possible contributions to these observed characteristics are discussed in terms of grain size, solute content, dislocation mechanisms and texture in the various systems.