Precipitation in stretched Al-Cu-Mg alloys with reduced alloying content studied by DSC, TEM and atom probe

摘要

The hardening and microstructural evolution during ageing of a Al-l.2Cu-0.5Mg and a Al-l.2Cu-l.2Mg (at.%) alloy has been investigated. Artificial ageing at 150℃ of stretched and naturally aged samples initially (up to about 48 h) leads to very limited further strengthening, but ageing at 190℃ results a quick increase in strength. Detailed microstructural investigation using differential scanning calorimetry, transmission electron microscopy and three-dimensional atom probe demonstrated that hardening at 150℃ is mostly dominated by the formation of solute clusters with varying compositions and plate-like zones rich in copper at early stages of ageing (t<24h) and by the formation of S phase at the later stages of ageing. At higher 190℃ no zones or clusters form and the ageing is dominated by the formation of S precipitates.