High-ductility AA6061 alloys produced by combination of sub-rapid solidification and Cr-alloying

Abstract

Fe-containing phases had a critical influence on the mechanical properties especially the ductility of Al–Mg–Si alloys. In the present study, the Fe-containing phases in Al-1.2Mg-0.7Si-0.1Fe (wt.%, AA6061) alloys had been regulated by the combination of sub-rapid solidification (SRS) and alloying with 0.12 wt.% Cr. Consequently, the coarse needle/platelet β-Al5FeSi phases (average length: ∼27 μm) were regulated as polyhedral α-AlCrFeSi phases with smaller size (∼2 μm) and uniform distribution. Based on the thermodynamic calculation of solidification paths, this study developed a possible mechanism of the Fe-containing phase transformation. Specifically, alloying with Cr accelerated the formation of fivefold symmetry icosahedral quasicrystal θ-Al13(Fe, Cr)4 phases (Al13M4 phases), which then combined with Si atoms in the surrounding melt and favored the formation of polyhedral α-AlCrFeSi phases. Tensile properties of artificial aged alloys were significantly improved by the combination of SRS and alloying with 0.12 wt.% Cr. The yield and ultimate strength increased from ∼254 to ∼293 MPa and ∼288–∼335 MPa, respectively, and the elongation to failure increased from ∼10% to ∼21%. This study may provide guidelines to produce high-ductility Al–Mg–Si alloys by optimizing the Fe-containing phases.