Control of kink-band formation in mille-feuille structured Al/Al2Cu eutectic alloys

Kink bands have recently received significant attention owing to their ability to increase the strength and ductility of some Mg alloys. In this study, we first demonstrated that it is also expected even in Al alloys, by controlling the morphology of the introduced kink bands. Several directionally solidified Al–Cu alloys, wherein an Al/Al2Cu eutectic lamellar microstructure developed, were focused, and the variations in deformation behavior with microstructure were examined. The alloys can be deformed at room temperature, and the yield stress exhibits strong anisotropy. A high yield stress appears when stress is applied parallel to the lamellar interface, accompanied by kink-band formation. The microstructure was found to play an important role in controlling kink-band formation and the resultant mechanical properties. Only a few large kink bands form in a eutectic alloy specimen with a full lamellar microstructure, which is accompanied by a lower yield stress. Thus, the kink band cannot be used positively in it. In hypoeutectic alloys in which primary Al grains coexist with the lamellar microstructure, however, significantly high yield stresses appear, which are accompanied by the homogeneous formation of small kink bands. The results demonstrate that microstructural control can vary the role of the deformation kink band from the fracture (buckling) mode to the deformation mode via the change in its morphology. This enables a large increase in yield stress while maintaining the ductility of the Al/Al2Cu eutectic alloy. The high yield stress is maintained at temperatures up to ~300 °C owing to the high thermal stability of the lamellar microstructure. These findings provide new ways to develop novel high-temperature high-strength Al alloys.