The microstructural evolution of a pre-alloyed AZ91 magnesium alloy powder through high-energy milling and subsequent isothermal annealing

This study analyzed the effect of high-energy milling (HEM) and subsequent isothermal annealing on the microstructural characteristics of a pre-alloyed AZ91 Mg alloy powder. To this end, the mentioned powder was milled for 14 h using a horizontal attritor. Then, the mechanically milled powder was isothermally annealed at temperatures ranging from 200 °C to 500 °C for 1 h up to 4 h in an Ar atmosphere. HEM caused the β-Mg17Al12 phase present in the microstructure of AZ91 powder particles to dissolve into their α-Mg solid solution matrix. In addition, the crystallite size of the α-Mg phase decreased to 25 nm through HEM. In contrast to the annealing time, the temperature of isothermal annealing had a significant effect on the microstructural features of the mechanically milled AZ91 powder.

► A nanostructured AZ91 Mg alloy was prepared by high-energy milling.
► The crystallite size of the milled AZ91 powder was measured to be 25 nm.
► The nanostructured AZ91 alloy was annealed at different temperatures for up to 4 h.
► Processed AZ91 Mg alloy presented a good thermal stability against grain growth.