Hydrogen-induced decomposition of Zr-rich cores in an Mg−6Zn−0.6Zr−0.5Cu alloy Original Research Article

This study presents the first experimental evidence of a hydrogen-induced decomposition reaction in an Mg–6Zn–0.6Zr–0.5Cu alloy from combined transmission electron microscopy and atom-probe tomography characterization. The reaction takes place due to the presence of H in the Mg matrix, causes the decomposition of pre-existing, high-temperature Zr–Zn intermetallic rods into Zr-rich hydride and β′ (Zn3Mg2), and forms novel composite precipitates in the Zr-rich cores of the alloy during ageing at 180 °C. The stoichiometry of the Zr–Zn rods was found to be Zn3(Zr1−x, Mgx)2, rather than Zn2Zr3, although both have a similar tetragonal crystal structure. The intrinsic link between the high-temperature Zr–Zn rods and the subsequent elongated composite precipitates, as depicted by the reaction, highlights the importance of engineering the Zr–Zn rod microstructures to control the final precipitate microstructure and effectively strengthen the Zr-rich cores, and hence the advanced Mg alloys.