High-resolution electron microscopy on the structure of Guinier-Preston zones in an Al-1.6 mass Pct Mg2Si alloy

The structure of the Guinier-Preston (GP) zone in an Al-1.6 mass pct Mg2Si alloy aged at 343 and 423 K was investigated by high-resolution transmission electron microscopy (HRTEM). The morphology of the GP zone is that of a fine plate having the dimensions of a monolayer in thickness, 2.5 nm in width, and less than 30 nm in length. Its elongated direction is parallel to the 〈100〉m direction. The chemical composition of the GP zone in an Al-Mg2Si alloy indicated a ratio of Mg/Si=1.0. The zones aggregate with increasing aging time and exhibit a more complicated morphology because of the transformation to the metastable phase that takes place inside the GP zones.