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, Al3Sc, can form by several different mechanisms, all of which are described. The precipitation kinetics of Al3Sc in binary Al–Sc alloys are discussed, and an overview of the reported influences of ternary alloying elements on the precipitation of Al3Sc is given. The Al3Sc 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 ...

http://www.arc.nucapt.northwestern.edu/refbase/files/Royset-2005.pdf

Scandium in aluminium alloys

The solidification behaviour of dilute aluminium–scandium alloys

The effect of scandium on the microstructure, mechanical properties and weldability of a cast Al–Mg alloy

The precipitation of coherent Al 3 Sc particles in Al–Sc alloys containing 0.06, 0.12 and 0.18 at.% Sc was investigated. The alloys were aged at 350°C for times up to 4663 h and the kinetics of particle growth, the particle size distributions and the evolution of particle morphology were measured and evaluated using transmission electron microscopy. Al 3 Sc precipitates did not nucleate homogeneously in the most dilute alloy; this result was unexpected because 0.06 at.% Sc exceeds the solubility limit at 350°C. Persistent dislocation networks were observed in the alloy containing 0.12 at.% Sc under normal solution treatment conditions (e.g. 1 h at 600°C) and the dislocations acted as heterogeneous nucleation sites. The dislocations were ultimately eliminated using a very long solution treatment time of ∼70 h near the melting temperature. Aging of both of the more concentrated alloys produced coherent precipitates. At short aging times the particles in the alloy containing 0.12% Sc were cauliflower-shaped and became spherical at longer times. At 4663 h some of the precipitates in this alloy were cuboidal, while others appear to have become semicoherent. The precipitates in this alloy were highly resistant to coarsening, and their size distributions were for the most part narrower than that predicted by the classical theory of Lifshitz, Slezov and Wagner (the LSW theory). The shapes of the precipitates in the alloy containing 0.18% Sc evolved from spherical to cuboidal with increasing aging time. The kinetics of growth of the precipitates in this alloy were consistent with the predictions of the LSW theory, the average size, 〈 r 〉, increasing with aging time, t , according to an equation of the type 〈 r 〉 3 ≃ kt . The experimentally measured rate constant, k , was in very good agreement with that calculated theoretically for this alloy.

/pdf/precipitation-of-al3sc-in-binary-al-sc-alloys-mpw04p8vd6.pdf

Precipitation of Al3Sc in binary Al–Sc alloys

http://www.dunand.northwestern.edu/refs/files/Nieh.pdf

High strain rate superplasticity in a continuously recrystallized Al-6%Mg-0.3%Sc alloy

Aluminium-rich alloys from the Al-Sc system were examined to determine the form of the equilibrium phase diagram and to obtain information on age hardening of chill cast alloys. Samples containing up to 8.75wt% Sc were examined using thermal analysis and optical microscopy. This work indicated a eutectic type of phase diagram with a eutectic temperature of about 665° C and a eutectic composition of about 0.6wt% Sc. The scandium-rich primary phase was found to be ScAl3 which is f c c with a lattice parameter of 0.4105nm. Chill cast samples of a 1 wt% Sc alloy were examined for their age hardening behaviour over the temperature range of 225 to 360° C. A maximum hardness of 77 VHN was obtained after ageing at 250° C for 3 days. This hardness was retained after ageing for a total of at least 12 days. The hardening precipitates were ScAl3 which were observed to form via a discontinuous precipitation mechanism. The ScAl3 precipitates were observed to have a parallel orientation relationship with the matrix.

N. Blake

Papers

Constitution and age hardening of Al-Sc alloys