Microstructural Characterization of Flexcast® Al-Mg Alloys with Scandium and Zirconium Additions

This contribution focuses on the microstructural characterization work performed on two Flexcast® Al-Mg alloys with Sc and Zr additions: one with and the other without Sc. In the as-cast state, both alloys showed fine Al- Fe intermetallic compounds along the solidification cell boundaries due to the high solidification rate in the belt caster. After heat treatment at 300°C, fine Al-Mn dispersoids were observed in both alloys. When the alloys were cold-rolled and aged at 300°C, the Sc-free alloy gradually recrystallized adjacent to constituents, while the Sc-containing alloy started to precipitate thermally stable L1₂ structured Al₃(Sc,Zr) particles. After heat treatment at 400°C, the Sc-free alloy exhibited Al-Mn dispersoids only and the cold-rolled alloy was fully recrystallized in less than 30 seconds. On the other hand, the Sc-containing alloy showed more enhanced precipitation of coherent Al₃(Sc,Zr) particles after aging at 400°C (1 minute) without recrystallizing. The highest strength of Flexcast® Al-Mg alloys was obtained in the Sc-containing alloy cold-rolled and aged at 300°C (4 hours) and this was ascribed to the combined effects of residual dislocations and coherent precipitates.