Trace element effects on precipitation in Al?Cu?Mg?(Ag, Si) alloys: a computational analysis

Abstract

In order to optimize mechanical properties of age-hardenable Al–Cu–Mg–(Ag, Si) alloys, the nucleation of the strengthening precipitate Ω must be enhanced while competing phases such as S and θ (or θ″/θ′) must be suppressed. One strategy is to promote the formation of the precursors, i.e., certain solute clusters that aid in Ω nucleation, using trace element additions such as Ag, and/or the elimination of deleterious impurities, e.g., Si. This paper describes the use of computational analysis tools to identify those elements that are either helpful or harmful. Using a multi-component quasi-chemical model, short-range-order parameters were calculated based on CALPHAD databases to indicate cluster formation in Al–Cu–Mg–(Ag, Si) solid solutions. To anticipate the orientation of the plate-like clusters that controls the habit-plane selection of the subsequent precipitates, the anisotropy of the associated strain was considered using the second order elastic tensors obtained from first principle total energy calculations.