Pii: S1359-6462(99)00345-0

In a recent paper, Li and Wawner [1] reported results of a study of the interaction between dislocations and {111}a precipitate plates of V (Al2Cu) phase in a plastically deformed Al-Cu-Mg-Ag alloy using both conventional and high resolution transmission electron microscopy (HRTEM). Based on experimental observations that V phase was sheared in plastically-deformed samples, they propose a strengthening model for aluminium alloys containing {111}a precipitate plates. This model is based essentially on the order strengthening mechanism, currently accepted for spherical particles [2,3], and includes increments in strength arising from both order strengthening and interfacial (chemical) strengthening for sheared precipitates. However, it does not take into account the plate-like shape and orientation of the V precipitates. Despite this major deficiency, the model is claimed to be applicable not only to V precipitate plates in Al-Cu-Mg-Ag alloys, but also to other {111}a precipitate plates, such as T1 (Al2CuLi) phase in Al-Cu-Li alloys [4,5]. The aim of this comment is to demonstrate that this model is an oversimplification and inevitably incorrect.