A considerable part of the available literature on scandium in aluminium alloys is reviewed. Experimental data and assessments of the binary Al-Sc phase diagram, a wide range of ternary Al-Sc-X phase diagrams and a few higher order phase diagrams are accounted for, with emphasis on the aluminium rich part of the diagrams. The phase which is in equilibrium with Al, Al 3 Sc, can form by several different mechanisms, all of which are described. The precipitation kinetics of Al 3 Sc in binary Al-Sc alloys are discussed, and an overview of the reported influences of ternary alloying elements on the precipitation of Al 3 Sc is given. The Al 3 Sc phase particles can serve as a grain refiner in the Al melt, a dispersoid for controlling the grain structure of the alloy and a strengthening precipitate. Several examples of these three effects are mentioned, both in binary Al-Sc alloys, and in more complex alloys. The reported effects of Sc on the precipitation behaviour in Al-Cu, Al-Mg-Si, Al-Zn-Mg and Al-Li alloys are also revised. A brief account of the effects of Sc additions on the corrosion behaviour of Al and Al-alloys is given. Finally, some views on the current and future use of Sc-containing Al alloys are given.

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