Abstract
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.
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Blake, N., Hopkins, M.A. Constitution and age hardening of Al-Sc alloys. J Mater Sci 20, 2861–2867 (1985). https://doi.org/10.1007/BF00553049
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DOI: https://doi.org/10.1007/BF00553049