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

摘要

The grain refinement effect and the ageing behaviour of Al–0.5 wt.% Sc, Al–0.7 wt.% Sc, and Al–1 wt.% Scalloys 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 isobserved 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 characterizedby a rich supersaturated solid solution in Sc, that promotes a great age hardening response at 250 C and300 C. The age hardening curves also demonstrate a low overageing kinetics for all the alloys. Althoughthe higher Sc content in solid solution for the alloys with 0.7 and 1 wt.% Sc, the age hardening response ofall the Al–Sc alloys remains similar. The direct age hardening response of the as cast Al–0.5 wt.% Sc isshown to be greater than the solutionised and age hardened alloy.