Effect of Mg Content on Al₃Sc-Dispersoid Formation in Cast Billets of Al-Mg-Sc Alloys

Small additions (0.05–0.1 at.%) of scandium to 5000 aluminum alloys (3–5 at.% Mg) can strengthen these alloys to make them competitive with high strength aluminum grades (e.g. 2000, 7000). A common issue with 5000 series aluminum alloys, however, is the formation of Lüders bands, strain heterogeneities caused by high concentration of Mg in solution. Scandium additions in aluminum alloys form Al₃Sc nano-dispersoids which can homogenize strain throughout the material, while zirconium additions stabilize the dispersoids to prevent coarsening. This study develops processing methods and compositions to optimize strength and formability in these wrought alloys. Coherent, semi-coherent, and incoherent precipitates were produced to study the effect of dispersoid size and to assess the tradeoff between production requirements and mechanical properties. Heat treatments were developed to attain these specific structures.