Diffusion kinetics, mechanical properties, and crystallographic characterization of intermetallic compounds in the Mg–Zn binary system

• A diffusion bonded sample is used to study structure and properties of Mg–Zn phases.
• SAED by TEM is used to characterize crystal symmetry and lattice parameters.
• Quasi-static indentation testing is used to determine mechanical properties.

Pure Mg was diffusion bonded to pure Zn at 315 °C for 168 h to produce equilibrium intermetallic compounds of the Mg–Zn system. All equilibrium phases at 315 °C, Mg21Zn25, Mg4Zn7, MgZn2, Mg2Zn11, were observed to develop. Concentration profiles by electron probe microanalysis, electron diffraction patterns by transmission electron microscopy, and load–displacement curves by nano-indentation were examined to characterize the phase constituents, crystal structure, diffusion kinetics, and mechanical properties. Mg21Zn25 with trigonal, Mg4Zn7 with monoclinic, and Mg2Zn11 with cubic structures were found and their lattice parameters were reported herein. Mg4Zn7 and Mg2Zn11 were observed to have a range of solubility of approximately 2.4 at% and 1.6 at%, respectively. Interdiffusion in MgZn2 occurred most rapidly, was an order of magnitude slower in Mg4Zn7 and Mg2Zn11, and was the slowest in Mg21Zn25. Composition-dependence of interdiffusion within each intermetallic phase was negligible. The intermetallic phases exhibited insignificant creep, but evidence of discontinuous yielding was observed. The average hardness and reduced moduli were similar for Mg21Zn25, Mg4Zn7, and MgZn2 phases, ∼5 GPa and ∼90 GPa, respectively. However, the Mg2Zn11 phase had lower hardness of 3.76 GPa and higher modulus of 108.9 GPa. The mechanical properties in the characterized intermetallic phases, exclusive of Mg21Zn25, were strongly concentration-dependent.