Microstructure and strength of commercial purity aluminium (AA 1200) cold-rolled to large strains

Commercial purity aluminium has been cold-rolled to reductions from 40 to 99% or true thickness strains (E,) from 0.5 to 5.0. Applying transmission electron microscopy techniques the microstructural evolution has been followed and structural parameters such as spacing between dislocation boundaries and misorientation angles across these boundaries have been measured and analyzed. This analysis shows that the microstructural evolution does not saturate at large strains. In parallel, the flow stress and strain hardening behavior has been determined by uniaxial tensile testing of rolled speciments. These stress-strain curves do not saturate in the strain range examined, even when changes in the Taylor M-factor are considered. This agrees with the evolution in the boundary spacing and misorientation angle, which are considered to be the strength determining parameters based on the operation of two mechanisms, dislocation strengthening and grain boundary strengthening. Following this description, the individual strength contributions are calculated and their addition leads to flow stress values and strain hardening behaviour in good agreement with those determined experimentally. (C) 2002 Published by Elsevier Science Ltd on behalf of Acta Materialia Inc.