A bimodal grain structured Al-Mg-Sc-Zr alloy with excellent strength and ductility by the combination of hot rolling and thermal-ECAP

The eminent role of equal channel angular pressing (ECAP) in enhancing the comprehensive mechanical properties of Al-Mg-Sc-Zr alloy is significant, even with inadequate formability. However, the combination of different thermal processing methods can solve this problem and the obtained strengthening mechanism and microstructure evolution remain largely unknown. In this study, the strength and ductility of Al-Mg-Sc-Zr alloy were synergistically improved by the combination processing of hot rolling (HR) and thermal-ECAP (T-ECAP). Specifically, the ultimate tensile strength, yield strength and failure elongation of ECAPed alloy (350 degrees C and 6 passes) reached 425 MPa, 291 MPa and 30.3 %, respectively. Grain refinement (from 5.1 mu m to 1.5 mu m) mainly produced by discontinuous dynamic recrystallization (DDRX) during multi-pass T-ECAP and the presence of nano-scale Al-3(Sc, Zr) particles (<21.2 nm) are essential to excellent strength, while high ductility is determined by the microstructure characteristics of low dislocation densities (<2 x10(13) m(-2)) and bimodal grain structure. The flinty micron-scale Al-3(Sc, Zr) phases promote recrystallization by pinning-induced dislocation accumulation to readily shape uniform refined-grain zones. After T-ECAP, the initial rolling texture gradually weakens and transforms into ECAP shear texture. The microstructure refinement caused by DDRX generates a deviation from the ideal shear texture position.