Effect of valence electron concentration on the glass forming ability in Al-based alloys

É. Fazakas, L.K. Varga

Metallic glasses-formation rules are mainly based on alloys with one or two principal components. The purpose of this paper is, by summarizing the microstructure characteristics of my and the reported Al-based glasses in terms of their atomic-size difference and enthalpy of mixing. The low GFA of Al- based alloys can be attributed to the relatively low heat of mixing and low relative atomic volume differences of the constituent elements. In addition, the lack of a deep eutectic at high Al-concentrations also contributes to the low GFA. By analyzing the density data of Al-based amorphous alloys, we have demonstrated that the atomic volumes (i.e., the metallic radii) are conserved during alloy formation and the rule of mixture can be applied for the average molar volume. A correlation was found between the crystallization temperatures and hardness values for the Al-based amorphous alloys. Furthermore, a correlation was found between the number of valence electrons and the hardness of Al-based amorphous alloys.  In this way, an electronic rule for the formation of amorphous alloys with high thermal stability and strength could be established: the larger the average total electron number, e/a (or the Pauling valency, VEC), the better the strength and stability.