The heterogeneous precipitation of the S (Al2CuMg) phase along dislocations was investigated using high-resolution transmission electron microscopy. Various configurations of the S precipitate group formed according to the initial dislocation morphology and no more than two S variants co-existed along a single dislocation line. The most favorable combination of two S variants was observed to be variants 1 and 4 (or variants 2 and 3), and the variant selection criterion for S precipitate with the classic orientation relationship was proved to be that the dislocation line direction lay in the habit plane of the precipitate. The contribution of S precipitate groups to strengthening was evaluated by comparing the difference in total system energy increment induced by precipitate loop and the equivalent number of Guinier–Preston–Bagaryatsky zones and discrete S particles during plastic deformation. The results showed that the average size of the precipitate loops as well as other kinds of precipitate groups had an important influence on the final strengthening effect. By keeping the precipitate groups below a critical size and increasing their density, the strength and thermal stability of the alloy were expected to be improved.

Variant Selection and the Strengthening Effect of S Precipitates at Dislocations in Al–Cu–Mg Alloy. Z.Q.Feng, Y.Q.Yang, B.Huang, X.Luo, M.H.Li, M.Han, M.S.Fu: Acta Materialia, 2011, 59[6], 2412-22