Preparation of high-strength Mg–3Al–Zn alloy with ultrafine-grained microstructure by powder metallurgy

Mg–3Al–Zn alloys with ultrafine grain size (UFG) have been fabricated by consolidation of ball milling nanocrystalline powders. Firstly, the elemental powders of Mg, Al and Zn were ball milled to synthesize nanocrystalline alloy powders. The milled powders stored in an Al container were sintered for 40 min at 633 K in a vacuum furnace. The sintered samples were extruded at the temperature range from 373 to 573 K for further densification. The bulk alloys with an average grain size of 180 nm showed a yield stress of 379 MPa, which was two times higher than that of the coarse-grained AZ31, and their ultimate strength was 417 MPa with a 5% elongation. The high strength of the alloys was attributed to three strengthening mechanism: the fine grain strengthening, dispersion strengthening and solid solution strengthening. Low strain hardening was observed in the UFG alloy, which may be caused by room temperature dynamic recovery during plastic deformation.