Evolution of Precipitate Structure and Age-Hardening Behavior of Al-Mg-Si-Zn Alloys with Different Mg/Si Ratios

Abstract:

The precipitation hardening behavior of Al-Mg-Si-Zn alloys with different Mg/Si ratios was studied by mechanical property test, differential scanning calorimetry, and high-angle annular dark-field scanning transmission electron microscope. The results show that the addition of Zn significantly increases the peak-aging hardness and yield strength of Mg-rich Al-Mg-Si alloys. There are three pathways for the transformation from the phase to the late-stage phases ( phase or phase) in Al-Mg-Si-Zn alloys during aging. The Mg-rich alloy is more likely to undergo transition from the phase to the phase, while the Si-rich alloy is more prone to experience transition from the phase to the phase. During the early and peak-aging stages, the Zn atoms enter the precipitates and occupy the energetically favorable atomic sites. During the over aging stage, the Zn atoms will gradually diffuse from the precipitate interior to the interface between the precipitates and the Al-matrix.