Al-Mg

Abstract: Interatomic potentials for pure Mg and the Mg-Al binary system have been developed based on the modified embedded-atom method (MEAM) potential formalism. The potentials can describe various fundamental physical properties of pure Mg (bulk, point defect, planar defect and thermal properties) and alloy behaviors (thermodynamic, structural and elastic properties) in reasonable agreement with experimental data or higher-level calculations. The applicability of the potential to atomistic investigations on the deformation behavior of pure Mg and the effect of alloying element Al on it is discussed.

Abstract: Different approaches are analyzed for construction of semi-empirical potentials for binary alloys, focusing specifically on the capability of these potentials to describe solid–liquid phase equilibria, as a pre-requisite to studies of solidification phenomena. Fitting ab initio compound data does not ensure correct reproduction of the dilute solid-solution formation energy, and explicit inclusion of this quantity in the potential development procedure does not guarantee that the potential will predict the correct solid–liquid phase diagram. Therefore, we conclude that fitting only to solid phase properties, as is done in most potential development procedures, generally is not sufficient to develop a semi-empirical potential suitable for the simulation of solidification. A method is proposed for the incorporation of data for liquid solution energies in the potential development procedure, and a new semi-empirical potential developed suitable for simulations of dilute alloys of Mg in Al. The potential correctly reproduces both zero-temperature solid properties and solidus and liquid lines on the Al-rich part of the Al–Mg phase diagram.

Abstract: Monte-Carlo simulations are done to determine Mg enrichment at various grain-boundaries of Al–10%Mg alloys at hot working temperatures. The interatomic potentials used in the simulations are developed using the force-matching method. The Mg segregation levels at the grain-boundaries are found to vary from 20% to 40%. The segregation enrichment differences at different grain-boundary sites are explained in terms of atomic size and local hydrostatic stress. The segregation level varies strongly with [110] tilt boundaries from low to high angle while showing minimal variation with [100] twist boundaries. Segregation levels are found to have some correlation with grain-boundary energy. The effect on grain-boundary decohesion due to Mg segregation is found to be a modest (10--35%) reduction in fracture energy compared to the fracture energy in pure Al.

Abstract: A set of embedded-atom method (EAM) potentials for Al-Mg alloys are developed using the "force matching" method. The potentials are fitted to both experimental data and a massive quantum mechanical database of atomic forces at finite temperatures. Using the potentials, Monte Carlo simulations are performed to study Mg segregation at different low-index surfaces of an Al alloy with 1–10 at% Mg. Surface enrichments of Mg of the order of 80% are found, and the segregation behavior is generally anisotropic. A set of discrete lattice-plane calculations, based on the nearest-neighbor broken-bond model corrected for strain energy, are shown to drastically reduce the anisotropy of surface segregation.