Materials science forum vol:331-3 issue:Part 1-3 pages:1095-1100
The effect of a solutionizing treatment on the precipitation sequence during ageing of an Al-4.22wt.%Mg-0.58wt.%Cu alloy at 180 degrees C has been studied by means of thermal analysis, mechanical testing and transmission electron microscopy. Precipitation and dissolution events observed by microcalorimetry and TEM have been related to changes in the yield strength during ageing of these alloys. Two types of precipitation mechanisms have been observed: precipitates were formed heterogeneously on dislocation loops and helices, but a homogeneous precipitation sequence in the matrix occurred as well. It has been shown that a long (30min at 525 degrees C) solutionizing treatment favours more the homogeneous precipitation sequence. After a short (10s at 525 degrees C) solutionizing treatment a more extensive heterogeneous precipitation on dislocations has been observed. In both cases, the rapid initial hardening of the alloy is attributed mainly to cluster - dislocation interactions. The peak of hardness which, after a short solutionizing treatment, is caused by the homogeneous precipitation of S' phase is rather modest compared to the one after a long solutionizing treatment. In the latter case the peak of hardness is additionally influenced by a massive homogeneous precipitation of fine S " and S' phases. Their effect on the precipitation hardening of the material at this stage is crucial.
ALUMINIUM ALLOYS: THEIR PHYSICAL AND MECHANICAL PROPERTIES, PTS 1-3