Bonding in MgSi and AlMgSi Compounds Relevant to AlMgSi Alloys

摘要

The bonding and stability of MgSi and AlMgSi compounds relevant to AlMgSialloys is investigated with the use of (L)APW+(lo) DFT calculations. We showthat the $\beta$ and $\beta''$ phases found in the precipitation sequence arecharacterised by the presence of covalent bonds between Si-Si nearest neighbourpairs and covalent/ionic bonds between Mg-Si nearest neighbour pairs. We theninvestigate the stability of two recently discovered precipitate phases, U1 andU2, both containing Al in addition to Mg and Si. We show that both phases arecharacterised by tightly bound Al-Si networks, made possible by a transfer ofcharge from the Mg atoms.