Hierarchical magnesium nano-composites for enhanced mechanical response

In this work we have synthesized and investigated the mechanical performance of a hierarchical magnesium (Mg) nano-composite with a novel micro-architecture including a reinforcing constituent that is a composite in itself. Specifically, we developed a nano-composite (alternatively referred to as a level II composite) with monolithic Mg as the matrix, reinforced by another level I composite comprising a sub-micron pure aluminum (Al) matrix in which are embedded nano-alumina (n-Al2O3) particles. The level II composite was obtained by adding a small volume fraction (vf) of the ball-milled level I composite to Mg using the powder metallurgy route followed by microwave-assisted rapid sintering and hot extrusion. Compared with the monolithic pure Mg, the hierarchical composites exhibited significant simultaneous enhancement of strengthening, hardening and failure strain, and also non-monotonic mechanical performance as a function of level I vf. Among the different hierarchical formulations synthesized, the hierarchical level I composition with 0.972% Al and 0.66% Al2O3 by volume (Mg/0.972 Al–0.66 Al2O3) exhibited the best overall mechanical properties compared with monolithic Mg, with an improvement of 96% in the 0.2% yield strength, 80% in the ultimate tensile strength, 42% in failure strain and 147% in the work of fracture. We identified and quantified some of the strengthening mechanisms that may be responsible for the impressive performance of this hierarchical nano-composite.