Precipitation hardening in Al-Cu-Mg alloys revisited

Transmission electron microscopy, differential scanning calorimetry and hardness tests have been used to study the precipitation sequence on artificial ageing of a stretched Al-Cu-Mg alloy. The samples were aged for different times at 150 and 190 degrees C, respectively. Some orthorhombic GPB2/S is present in samples aged at 150 degrees C for 48 h, which is at the very start of the second stage of hardening. The combined experiments clearly show that the second stage hardening is dominated by S phase, which forms a dense precipitate structure at the peak hardness stage, whilst no significant amounts of other phases or zones are detected. (c) 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.