Coordinating the deformation of a low-alloyed magnesium alloy for a superior combination of strength and ductility through core-shell structured reinforcements

The trade-off between strength and ductility is a longstanding puzzle in metallic materials. Here we present a novel strategy to acquire simultaneously high strength and ductility in a low-alloyed Mg-3.16Zn-0.97Ca-0.55Al-0.44Ag (wt.%) alloy by forming special core-shell structured reinforcements in grain interior through a modified thixoforming technique. The core-shell structured reinforcements consist of inner core of MgZn ₂ second-phase particles (SP _p) and outer shell of a transition zone rich in nano- β 1 ′ (Mg ₄Zn ₇) precipitates. A superior combination of strength and ductility is achieved in the magnesium alloy with an excellent strengthening and toughening efficiency, which is better than the existing counterparts where precious rare earth elements or more elements are contained. At initial deformation stage, the transition zone (1.41 GPa in hardness) mitigates the sharp strain gradient between the hard SP _p (1.85 GPa) and soft matrix (822 MPa) by intensifying dislocation accumulation. Subsequently, excessive < 1 ¯ 011>{10 1 ¯ 2} twins are emitted from SP _p, leading to the successive formation of quilted-looking twins, apparent crossing twins, double twins and real crossing twins that prevailed with type dislocations where secondary {10 1 ¯ 1}-{10 1 ¯ 2} and {10 1 ¯ 2}-{10 1 ¯ 2} twins occur. The formation of twin networks in three-dimension facilitates quadruple interaction between dislocation, twin, precipitate and SP _p, promoting the overall deformation coordination and leading to an enhanced work hardening. This work provides a promising strategy to produce high-performance magnesium alloys at a considerably low cost.