Metastable phases in an Al-Mg-Si alloy containing copper

The Q ' phase in an Al-1.0 mass pet Mg2Si-0.5 mass pet Cu alloy at a peak-a ged condition of 523 K was observed by a high-resolution transmission elect ron microscope (HRTEM), in order to identify its structure and chemical com position, and was compared with the type-C precipitate in an Al-1.0 mass pe t Mg2Si-0.4 mass pet Si alloy (the excess-Si alloy). The Q ' phase has simi lar features to the type-C precipitate, according to results of electron di ffraction patterns and images taken by the HRTEM, that is, they have simila r hexagonal crystal lattices (a = 1.04 nm and c = 0.405 nm) to each other. The type-C precipitate in the excess-Si alloy was the ternary Al-Mg-Si phas e, and the Q ' phase was the quaternary Al-Mg-Si-Cu phase in the Al-Mg-Si-C u alloy, as determined by energy-dispersive X-ray spectroscopic (EDS) analy sis.