Effects of grain refinement and precipitate strengthening on mechanical properties of double-extruded Mg-12Gd-2Er-0.4Zr alloy.

The Mg-12Gd-2Er-0.4Zr (GE122K) is fabricated by double extrusion, and the effects of grain refinement and precipitate evolution on the mechanical performance of the extruded alloys are deeply analyzed. Scanning electron microscope results spectacle that some bulky precipitates in the single extruded alloy are fragmented to fine precipitates during double extrusion and distribute linearly along the extrusion direction (ED). The fine precipitates exhibit the strongest dispersion strengthening effect, whereas the bulky precipitates act as crack resources and decrease the elongation. After double extrusion, a refined grain structure with an average grain size of 2.7 µm is achieved, which is attributed to dynamic recrystallization (DRX). Moreover, double extrusion boosts the content of rare-earth elements into the matrix by dissolving the fine precipitates. During aging, extensive β′ precipitates form in the double extruded alloy than in the single extrude alloy. As a result, refined grains and strong precipitation strengthening make a significant contribution to a high yield strength (YS) of 422 ± 1.59 MPa with an elongation (EL) of 6.5 ± 0.89% in the double extruded+peak-aged alloy (ACX2). The possible strengthening mechanisms are discussed, and it is found that grain refinement and precipitate strengthening are the main contributors to the high strength of the GE122K alloy. Fabrication of Mg-12Gd-2Er-0.4Zr (wt%) alloy via double extrusion+aging with excellent mechanical performance. [Display omitted] • A facile and robust fabrication mechanism is adopted to attain an excellent balance of yield strength and elongation. • Grain refinement and precipitates have different effects on the strength of Mg-12Gd-2Er-0.4Zr alloy. • The β′ precipitate strengthening is the dominate strengthening mechanism during aging treatment of the extruded alloys. [ABSTRACT FROM AUTHOR]