Abstract:The valence electron structures of Al-Mg alloy with minor Sc and Zr were calculated according to the empirical electron theory(EET) in solid. The results show that because of the strong interaction of Al atom with Zr and Sc atom in melting during solidification, the Al₃Sc and Al₃(Sc_1-xZr_x) particles which act as heterogeneous nuclear are firstly crystallized in alloy to make grains refine. In progress of solidification, the Al-Sc, Al-Zr-Sc segregation regions are formed in solid solution matrix of Al-Mg alloy owing to the strong interaction of Al atom with Zr, Sc atoms in bulk of alloy, so in the following homogenization treatment, the finer dispersed Al₃Sc and Al₃(Sc_1-xZr_x) second-particles which are coherence with the matrix are precipitated in the segregation region. These finer second-particles with the strong Al—Zr, Al—Sc covalent bonds can strengthen the covalent bonds in matrix of the alloy, and also enhance the hardness and strength of Al-Mg alloy. Those finer second-particles precipitated in interface of sub-grains can also strengthen the covalence bonds there, and effectively hinder the interface of sub-grains from migrating and restrain the sub-grains from growing, and cause better thermal stability of Al-Mg alloy.

Key words: Al-Mg alloy; Zr; Sc; covalent bond; grain refinement; mechanical properties