Is Mg17Al12 ductile or brittle? A theoretical insight

Abstract

The Mg 17 Al 12 -phase, which is common and important in Mg-Al alloy, has long been regarded as a brittle phase in experiments but theoretical calculations report controversial results. To unravel why theoretical calculations report controversial results and determine whether Mg 17 Al 12 is brittle or ductile, density functional theory calculations on atomic level are performed to investigate mechanic properties of Mg 17 Al 12 without containing alloying elements and without taking the size effect. The results showed that the parameter k -point played critical role in the DFT-based elastic calculations. The convergent G/B ratio of Mg 17 Al 12 was about 0.52, suggesting that the Mg 17 Al 12 -phase was theoretically ductile although its ductility was poor. The chemical bonding in Mg 17 Al 12 was the mixture of metallic Mg-Mg bond and covalent Al-Al bond. The advantage of metallic bonding over covalent bonding provided a possible explanation for the ductility of Mg 17 Al 12 . Possible reasons for the brittleness of Mg 17 Al 12 in experiments are also discussed.