Dendritic Growth, Solidification Thermal Parameters, and Mg Content Affecting the Tensile Properties of Al-Mg-1.5 Wt Pct Fe Alloys

Abstract

Al-Mg-Fe alloys are appointed as favorable ones with respect to the costs and all the required properties for successful vessel service. However, the experimental inter-relations of solidification thermal parameters, microstructure, and mechanical strength are still undetermined. In the present research work, the dependences of tensile properties on the length scale of the dendritic morphology of ternary Al-1.2 wt pct Mg-1.5 wt pct Fe and Al-7 wt pct Mg-1.5 wt pct Fe alloys are examined. Transient heat flow conditions during solidification have been achieved by the use of a directional solidification system, thus permitting a comprehensive characterization of the dendritic microstructures to be performed. Thermo-Calc computations, X-ray diffraction, and scanning electron microscopy analyses are carried out to give support to the extensive microstructural evaluation performed with both ternary Al-Mg-Fe alloys. Experimental growth relations of primary, λ ₁, and secondary, λ ₂, dendrite arm spacings with cooling rate (${\dot T}_{\rm{L}}$) and of tensile properties with λ ₂ are proposed. For both alloys examined, Hall–Petch type formulas show that the tensile strength increases with the decrease in λ ₂. The soundest strength–ductility balance is exhibited by the Al-7 wt pct Mg-1.5 wt pct Fe alloy specimen with refined microstructure. This is shown to be due to a more homogeneous distribution of intermetallic particles in connection with solid solution strengthening propitiated by Mg. Functional experimental inter-relations of tensile properties with growth (V _L) and cooling rates (${\dot T}_{\rm{L}}$) for both ternary Al-Mg-Fe alloys have also been derived.