Mechanical Properties of a Heat-Treatable Al-Sc Alloy Reinforced with Al2O3 Dispersoids

The mechanical behavior of precipitation-strengthened Al-0.18 wt.% Sc alloys containing 30 vol.% Al2O3 dispersoids is studied at 25, 300 and 350°C. The effect of Al3Sc precipitate size is studied by varying aging treatments. Microhardness measurements show that both populations of particles (nanometer-sized Al3Sc precipitates and submicron-sized Al2O3 dispersoids) contribute to strength at ambient temperature. At elevated temperature, a threshold stress is observed, indicative of interactions between matrix dislocations and the particles. The threshold stress is significantly higher than either Al0.18 wt.% Sc alloys without Al2O3 dispersoids or Al-30 vol.% Al2O3 without Al3Sc precipitates. This indicates that strengthening is occurring at both length scales and in a nonlinear manner, as the reinforced alloy exhibits strength higher than the sum of the strengths of Al-Sc and Al-Al2O3 alloys.