HRTEM OBSERVATION OF PRECIPITATES IN Al-Mg-Si ALLOY WITH COPPER

摘要

The Q' phase in the Al -1.0 mass percent Mg_2Si - 0.5 mass percent Cu alloy at a peak aged condition of 523 K was observed by a high resolution transmission electron microscope in order to identify its structure and chemistry, and was compared with the type-C precipitate in the Al- 1.0 mass percent Mg_2Si -0.4 mass percent Si (the excess Si alloy). The Q' phase had a similar feature to the type-C precipitates. The type-C precipitates 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 by the energy dispersive X-ray spectroscopic (EDS) analysis. It is possible to explain about the formation of ternary or quaternary metastable phases in Al-Mg-Si alloys in the same way as the formation of quaternary phases in the Al-Cu-Mg-Si alloys.