Strength and ductility enhancement of twin-roll cast Al-Zn-Mg-Cu alloys with high solidification intervals through a synergistic segregation-controlling strategy

Abstract

Center segregation and banded intergranular segregation (B-IGS) should be well controlled to improve the mechanical properties of twin-roll cast (TRC) aluminum alloys, especially for alloys with high solidification intervals. In the present work, a synergistic grain refinement strategy was designed using an Al-5Ti-B grain refiner and Ti, Zr, and Sc microalloying elements to simultaneously control center segregation and B-IGS in TRC Al-Zn-Mg-Cu alloys. As the grain size decreased, center segregation defects were eliminated and transformed into dispersed B-IGS defects; simultaneously, the width and length of the B-IGS were also reduced. Moreover, the macro-distributions of the alloying elements along the thickness direction became more homogeneous due to a weak shear-induced dilation effect. The well-controlled multiscale segregation improved the uniformity of the alloy macrostructure, accelerated the redissolution of the crystalline phase, dispersed the aggregated residual phase, and refined grains under the T6 state. Hence, the strength and ductility of the alloys under the T6 state were simultaneously improved, and the hardness distribution along the thickness direction became more homogenous. Furthermore, the underlying mechanisms of segregation evolution and strength and ductility enhancements were elucidated. This work provides a novel strategy to effectively control multiscale segregation and produce high-performance aluminum alloys with high solidification intervals by TRC.