The influence of precipitation on plastic deformation of Al-Cu-Li alloys

The plastic behaviour of two recently developed Al-Cu-Li alloys with different Cu/Li ratios, AA2198 and AA2196, was studied as a function of precipitation state by tensile tests, strain hardening rate analysis, Bauschinger tests, slip line imaging and atomic scale characterization of precipitate shearing by advanced electron microscopy. For early ageing times where delta' and/or solute clusters are present, plasticity occurs heterogeneously, the strain hardening rate is high, and the Bauschinger effect is moderate. When T-1 precipitates are present, plasticity becomes more homogeneous, and the strain hardening rate shows a slower decrease compared with other aluminium alloys containing shearable precipitates. In addition, these ageing conditions show a high reversibility of plastic strain, and it is observed that precipitates are sheared only by single steps. The possibility of a specific shearing mechanism of the T-1 phase is discussed in light of these results. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.