Atomic Bonding and Properties of Al–Mg–Sc Alloy

Abstract

Atomic bonding of Al–Mg alloy with minor Sc is calculated according to the “Empirical electron theory in solid” (EET). The results show that the particles Al₃Sc precipitate firstly in melting during solidification is owing to the strong interaction of Al with Sc atom. The strong interaction of Al with Sc atom can also cause to form the Al–Sc and Mg–Sc segregation regions in solid solution matrix of Al–Mg alloy in further process of solidification. So in following homogenization treatment, finer dispersed Al₃Sc second-particles owing to its strong Al–Sc covalent bonds are easily precipitated in these segregation regions. These secondary tiny Al₃Sc particles coherent with the matrix can hinder the recrystallization of the alloy under high temperature by pinning the grain boundary. The reason, that the large Al₃Sc particles can improve the strength and hardness of the alloy, is attributed to the strong Al–Sc covalent bond net in larger Al₃Sc particles which are difficultly sheared by dislocation.