Improved strength-ductility with bimodal microstructure composed of kink-strengthening grains in a layer-structured Mg-Al-Y alloy

We report that a mille-feuille-type layer-structured Mg-Al-Y alloy shows a remarkably improved strength-ductility balance after applying a hot-extrusion process, which successfully generates a unique bimodal microstructure consisting of fine recrystallized grains and large kink-deformed grains. The strength originates primarily from the work-hardened large grains composed of a large number of kink boundaries (KBs), while the ductility is mainly due to the recrystallized grains that are almost free from defects. On the contrary to the significant solute-segregations at the KBs observed so far for the most kink-strengthened Mg-transition-metal-rare-earth alloys, the present Mg-Al-Y alloy exhibits notably weak solute-segregations, hence suggesting that the solute-segregation is not an essential factor to realize the KB strengthening effect. The solute-segregation behaviors as well as the layer-structure stability are discussed based on solute-pair interaction energy calculations and solute diffusion kinetics during the initial heat treatment and the hot-extrusion process.