Effects of Ag Microalloying on Precipitated Phase Structure of Al-Mg-Si Alloy
The precipitated phase structure of Al-Mg-Si-Ag alloy was systematically investigated by first-principles calculation and spherical aberration corrected transmission electron microscopy in aspects of formation enthalpy,charge density and atomic scale microstructure.The results indicate that the stability of β″ phase is decreased after Ag microal-loying,and Ag atoms tend to segregate at the β″ phase/matrix interface,which is mainly attributed to the electron grabbing effect of Ag.Ag microalloying is beneficial to the structural stability of β′ phase.Ag atoms can enter the inte-rior of β′ phase,possibly occupying the Si1 and Si2 positions,and the formation enthalpy is lower than that of β″phase,promoting the transformation of β″ phase into β′ phase,which is related to the strong covalent bond between Ag-Al atoms.Ag microalloying is adverse to the structural stability of β phase,which results from the weak bond strength between Ag-Mg atoms.
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