Mechanical Properties and Microstructure of Al – Sc with Rare - Earth Element or Al 2 O 3 Additions

Mechanical Properties and Microstructure of Al–Sc with Rare-Earth Element or Al2O3 Additions Richard Albert Karnesky, Jr. Aluminum alloys strengthened with coherent (L12), nanosize Al3Sc precipitates are structural materials that have outstanding strength at ambient and elevated temperatures. They are creep resistant at 300 ◦C and exhibit a threshold stress, below which creep is not measurable. Introducing ternary alloying additions, such as rare-earth elements (RE=Y, Dy, Er), that segregate within Al3Sc precipitates improves this creep resistance by increasing the lattice parameter misfit of precipitates with Al. In this thesis, Al–600 Sc–200 RE and Al–900 Sc–300 Er (at. ppm) are studied. These elements are an order of magnitude less expensive than Sc, so reduce alloy costs. As an alternative or supplement to ternary additions, submicron (incoherent) Al2O3 dispersoids impart additional strengthening. The dispersion-strengthened cast alloys, DSC–Al–1100 Sc and DSC–Al–800 Sc–300 Zr, studied in this thesis contain 30 vol.% Al2O3.