The effect of Sc additions on the microstructure and age hardening behaviour of as cast Al-Sc alloys

The grain refinement effect and the ageing behaviour of Al-0.5 wt.% Sc, Al-0.7 wt.% Sc, and Al-1 wt.% Sc alloys are studied on the basis of optic microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) observations and hardness measurements. In Al-Sc alloys the higher grain refinement is observed for Sc contents greater than 0.5 wt.% accompanied by a notorious morphology modification, from coarse columnar grains to a fine perfect equiaxed structure. The as cast structures are characterized by a rich supersaturated solid solution in Sc, that promotes a great age hardening response at 250 degrees C and 300 degrees C. The age hardening curves also demonstrate a low overageing kinetics for all the alloys. Although the higher Sc content in solid solution for the alloys with 0.7 and 1 wt.% Sc, the age hardening response of all the Al-Sc alloys remains similar. The direct age hardening response of the as cast Al-0.5 wt.% Sc is shown to be greater than the solutionised and age hardened alloy. (c) 2012 Elsevier Ltd. All rights reserved.