Metastable Phases in an Al-Mg-Si Alloy Containing Copper

Abstract

Alloy studied a lab sample with 0.5pct Cu mass content. The Q’phase in an Al-1.0 mass pct Mg2Si-0.5 mass pct Cu alloy at a peak-aged condition of 523 K was observed by a high-resolution transmission electron microscope (HRTEM), in order to identify its structure and chemical composition, and was compared with the type-C precipitate in an Al-1.0 mass pct Mg2Si-0.4 mass pct Si alloy (the excess-Si alloy). The Q'phase has similar features to the type-C precipitate, according to results of electron diffraction patterns and images taken by the HRTEM, that is, they have similar hexagonal crystal lattices (a 5 1.04 nm and c 5 0.405 nm) to each other. The type-C precipitate in the excess-Si alloy was the ternary Al-Mg-Si phase, and the Q' phase was the quaternary Al-Mg-Si-Cu phase in the Al-Mg-Si-Cu alloy, as determined by energydispersive X-ray spectroscopic (EDS) analysis. 6061 is mentioned once.