Aluminium scandium alloys

Scandium is the first of the transition elements and occupies an intermediate position between the typical rare-earth elements and the light metallic elements. The most significant technological potential for scandium is as an alloying element in aluminium. Indeed, extensive research has demonstrated that a minor alloying addition of scandium can result in a major increase in strength, with reports of a 50–100 MPa increment per 0.1 wt.%Sc added. This enhanced strength can be attributed to the fine spherical L12 Al3Sc dispersoids, typically with a diameter under 10 nm. Sc acts as a solid solution hardener and Al3Sc as a precipitation hardener and recrystallization inhibiter and has also been reported to act as a favourable nucleation site for strengthening phases. This increase in strength is generally accompanied by an improved or stable ductility and the strong antirecrystallization of Al3Sc enables the creation of superplastic alloys, formable at strain rates up to 10− 2 s− 1. Finally, scandium has been reported to improve various corrosion-related properties. In this chapter, a brief history and details of the chemical and physical metallurgy of the scandium element will be presented. The impact of scandium on phase transformations, microstructure, and bulk properties in the industrially relevant Al alloys (casting and wrought, heat-treatable, and nonheat-treatable) is reviewed. A particular emphasis on the interaction between scandium and other alloying elements is also outlined.