High strength-ductility synergy induced by sub-rapid solidification in twin-roll cast Al–Mg–Si alloys

Abstract

Regulating the morphology and composition of Fe-containing phases can significantly improve the mechanical properties of Al–Mg–Si alloys. Here, we successfully prepared the high-performance AA6061 alloys by the route of sub-rapid solidification (SRS) based on twin-roll casting (TRC). Excellent tensile strength (∼372 MPa) and elongation (∼19%) were achieved in the peak-aged TRC sample, which increased simultaneously compared with the counterpart (∼351 MPa and ∼14%) fabricated via ingot casting (IC). It was found that the strength-ductility synergy of the TRC sample was caused by the high cooling rate, wherein the SRS can refine the microstructure significantly and promote the reaction from the AlFeSi to the AlFeMgSi (Mg:Fe:Si = 1:1.5:2.5) phase. The centerline segregation in the TRC strip could be well mitigated during solution treatment because the reduced size and Mg-incorporation accelerated the redissolution of AlFeMgSi phases. The alleviative segregation greatly promoted supersaturated solution, and thus contributing to the synergy of strength and ductility. Meanwhile, the Si-rich AlFeMgSi phase could decompose into the Fe-rich α-AlFeSi (Fe:Si > 1) during solution treatment, which expanded the solid solubility of Si and Mg. Therefore, an enhanced aging hardening response was obtained in the peak-aged TRC sample, showing the high number density and volume fraction of β” phase. The results would provide guidelines for developing high-performance Al–Mg–Si alloys based on the SRS during TRC.