Significantly improved particle strengthening of Al–Sc alloy by high Sc composition design and rapid solidification

Abstract

Sc alloying is usually carried out by adding a small amount of Sc in typical aluminum alloys to improve the mechanical properties, however, the effect of high-Sc content on the microstructure and properties of aluminum alloys is rarely concerned. To further understand the role of Sc alloying, several Al–Sc binary alloys with high-Sc content are designed and the relationship between the Sc content and mechanical properties were investigated. It is found that the mechanical properties of Al–Sc binary alloy is determined by both the Sc content and the cooling rate. The addition amount of Sc shows relatively small effect on the mechanical properties at low cooling rate, but higher at high cooling rate, because cooling rate turns the size and distribution of Al3Sc particles. Through the high Sc content alloy design and melt spinning rapid cooling technology, the densely distributed Al3Sc precipitate of about 250 nm can be located inside the α-Al grains, resulting in the intracsystalline reinforcement. The combination of high tensile strength (344 MPa) and good plasticity (5.7%) were achieved at a grain size of ~500 nm in the hypereutectic Al–Sc binary alloys ribbons. The significant strengthening could be attributed to multiple strengthening mechanisms including (1) Orowan strengthening; (2) coefficient of thermal expansion (CTE) mismatch strengthening; (3) the Hall-Petch effect caused by grain refinement; (4) solid solution strengthening. When the cooling rate is increased, the effects of thermal mismatch strengthening and Orowan mechanism are more prominent, significantly improving the strength of the Al–Sc alloy. The present experimental results provide an insight into the understanding of microstructural evolution of nanoparticles, and extend the effort for the development of hypereutectic Al–Sc alloys as a member of high-strength structural materials.