Abstract
The Al-Mg-Si-Cu (6xxx) alloys are widely used for industrial purposes due to their high strength, formability and resistance against corrosion. These are heat-treatable alloys, which are characterized by a large increase in hardness upon ageing. The strengthening effect is found to be caused by interface strain between the Al-matrix and small, semi-coherent, metastable precipitates that form in solid solution. The precipitation sequence is reported to be:super saturated solid solution (SSS)-> atomic clusters-> GP zones->beta'', L/S/C, QP, QC, ', Q'-> QTo optimize alloy composition for achieving specific properties, detailed information on theprecipitate structure and morphology is required. Since the metastable phases are so small (~nm), they can readily be investigated with a transmission electron microscope (TEM). Recentadvances in high-resolution TEM (HRTEM) imaging and quantitative electron diffractiontechniques have enabled the crystal structures of most precipitates in the Al-Mg-Si system tobe solved [4-7]. This paper reports the refined crystal structures of the Q’ phase and that ofthe C-plate precipitate. Initial models were derived based on experimental data, and were furtherimproved by quantitative analysis of electron diffraction data.
