Aging Behavior of Flexcast® Al-Mg Alloys with Sc and Zr Additions

Abstract

AA5xxx series Al alloys have presented great potential in recent decades for packaging and automotive applications. A recent further development of these alloys has been the addition of Sc and Zr. The presence of these elements is known to develop strengthening phases that also influence other metallurgical phenomena such as recovery and recrystallization. However, the low solubility of both Sc and Zr in Al requires high cooling rates during casting in order to attain a supersaturated solid solution which conventional DC casting is unable to achieve. In this study, two Al- 3%Mg alloys, one Sc-free and the other containing 0.4% Sc were cast using the Flexcaster® available at the Novelis Global Technology Center (Kingston, Ontario). The Flexcaster® is a strip casting technology that transforms liquid aluminum into a directly rollable cast ingot that is not subject to scalping or homogenization processing. This technology is characterized by relatively high solidification and cooling rates. Aging experiments were performed on as-cast and cold-rolled samples of the two alloys to study the evolution of strengthening phases and their impact on recovery and recrystallization. Both alloys were artificially aged following casting at 200, 300 and 400°C for times ranging from 30s to 72 hours. The alloys were characterized by hardness and tensile tests and electrical resistivity measurements as well as optical and electron microscopy in order to monitor the aging behavior of the alloys. Results show enhanced strengthening in the Sc-containing alloy and superior high temperature microstructural stability in comparison to the Sc-free alloy as well as conventionally cast AlMgSc alloys.