Microstructures and mechanical properties of the ultrafine-grained Mg–3Al–Zn alloys fabricated by powder metallurgy

• The Mg–3Al–Zn powders with nano-MgO particles have been successfully fabricated.
• The recrystallization behavior induced by warm extrusion was studied.
• The contribution ratios of ultrafine grains and nano-MgO hardening were calculated.
• The grain size and center-to-center spacing of nano-MgO particles were determined.

The ultrafine-grained Mg–3Al–Zn alloys were successfully fabricated by the method of mechanical milling, cold press consolidation and warm extrusion. The effect of extrusion temperature on the microstructure and compression properties of the as-extruded samples has been investigated. The results indicate that with the increase of extrusion temperature from 423 K to 473 K, full dynamic recrystallization (DRX) behavior replaces partial DRX, while the average grain size increases from 246 nm to 499 nm. The uniformly dispersioned nano-MgO particles derived from mechanical milling could significantly enhance the compressive properties of as-extruded samples. The yield strength, ultimate compression strength, and fracture strain of the as-extruded alloy with an average grain size of 246 nm are, respectively, 508.0 MPa, 512.8 MPa and 9.2%. The high strength of the alloy is principally ascribed to ultra-fine grained structure and nano-MgO dispersion strengthening, and the contribution ratios are 23.58% and 62.36%, respectively.

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