Effects of thermomechanical treatment on the microstructure, precipitation strengthening, internal friction, and thermal stability of Al–Er-Yb-Sc alloys with good electrical conductivity

Abstract

Rare-earth elements improve the mechanical properties of aluminum owing to the formation of the L12-structured nanoprecipitates providing the precipitation strengthening effect. The precipitates type, size, and number density depend on the alloy chemical composition and a thermomechanical treatment regime. It is essential to develop the alloys and treatments, providing a combination of the enhanced mechanical strength and a high level of electrical conductivity. This study investigates the influence of thermomechanical treatments on the microstructure, precipitation strengthening, mechanical properties, and electrical conductivity of Al–Er-Yb-Sc alloys with differing Sc content. An as-cast structure of the alloys studied consists of a supersaturated aluminum solid solution and Al3(Er,Yb) phase particles of eutectic origin with the particle thickness of 50–200 nm. A significant strengthening during post-deformation annealing is achieved by precipitation of L12-Al3(Sc,Er,Yb) phase dispersoids of 4–8 nm in size. The mechanical spectroscopy method is successfully used to understand the precipitation kinetics of the studied alloys in comparison with analogous Al-Yb-Y-Sc alloys. This method is highly sensitive to lattice defects parameters, i.e., recrystallization and precipitation kinetics. High-scandium alloys demonstrate an increase of the hardness and tensile strength and insignificant changes in the internal friction background level during post-deformation annealing of cold-worked samples at 300 °C. The yield strength of the Al–Er-Yb-Sc alloys after post-deformation annealing is 142–231 MPa, elongation-to-failure is 3.6–13.5%, and electrical conductivity is 54.8–60.9% IACS, dependent on scandium content and annealing parameters. The studied alloys exhibit high thermal stability of the tensile properties, which remains unchanged during annealing at 300 °C for 100 h.