High-resolution electron microscopy on the structure of guinier-preston zones in an Al-1.6 mass Pet 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.