Sammendrag
The β″ phase is the major hardening precipitate in Al-Mg-Si alloys. It was studied by atomistic
calculations based on density functional theory (DFT), using an atomistic model where the
precipitate was embedded in an Al matrix. This allowed quantifying and visualizing the
coherency strain in the matrix and within the precipitates. The elastic strain was found to
decrease exponentially in the matrix as a function of distance from the precipitate interface. The
formation enthalpy of several different chemical compositions of β″ was calculated, and the
most stable composition was found to be Mg5Al2Si4. A study of the calculated valence charge
density and electron localization function showed that the covalency network between Si-atoms
in the precipitate structure is broken when the precipitate contains Al.
calculations based on density functional theory (DFT), using an atomistic model where the
precipitate was embedded in an Al matrix. This allowed quantifying and visualizing the
coherency strain in the matrix and within the precipitates. The elastic strain was found to
decrease exponentially in the matrix as a function of distance from the precipitate interface. The
formation enthalpy of several different chemical compositions of β″ was calculated, and the
most stable composition was found to be Mg5Al2Si4. A study of the calculated valence charge
density and electron localization function showed that the covalency network between Si-atoms
in the precipitate structure is broken when the precipitate contains Al.