Fe-bearing phase formation, microstructure evolution, and mechanical properties of Al-Mg-Si-Fe alloy fabricated by the twin-roll casting process

The composition and morphology of the Fe-bearing phase play a significant role in the mechanical properties of aluminum (Al) alloy sheets. In this work, we have studied the formation of Fe-bearing phases in an Al-0.53Mg-0.69Si-0.14Fe (wt%) alloy under the twin-roll casting (TRC) and the direct chill casting (DC) processes, respectively. We found that the pi-AlFeMgSi phase was formed in the as-cast TRC sample, while the beta-AlFeSi phase was formed in the as-cast DC sample. The differences in the formation of Fe-bearing phases are attributed to the promotion of the peritectic reaction to form the pi-AlFeMgSi phase via the TRC process. Furthermore, after homogenization treatment at 550 degrees C and 2 h, the pi-AlFeMgSi phase in the as cast TRC sample completely decomposed into the fine beta-AlFeSi phase, while it was insufficient to dissolve the beta-AlFeSi phase in the as-cast DC sample. This is owing to the lower dissolution temperature of the pi AlFeMgSi phase compared to the beta-AlFeSi phase. The decomposition of the pi-AlFeMgSi phase expands the solid solubility and promotes the aging precipitation, resulting in higher yield strength of the TRC sample than that of the DC sample during the peak-aging treatment. Our work provides new insight into the development of high-performance AA6xxx series alloys based on the TRC process. (c) 2021 Elsevier B.V. All rights reserved.