Effects of Al addition on microstructure and mechanical properties of extruded Mg-Y-Zn-Co alloy

Abstract

The effects of Al addition on microstructure and mechanical properties of an extruded Mg-Y-Zn-Co (MYZC) alloy were investigated. The addition of Al into the alloy refined dendrite of as-cast MYZC alloy, promoted the precipitation of a great number of long period stacking order (LPSO) phases with a 18R structure at dendritic boundaries and facilitated the formation of (Al,Zn)₂Y phases. After homogenization treatment, a fraction of the lamellar 18R-LPSO phases at grain boundaries transformed into the fine strip-like 14H-LPSO phases within the grains. During extrusion, compared with the extruded MYZC alloy, the extruded Mg-Y-Zn-Co-Al (MYZCA) alloy exhibited a finer grain size of ∼2.76 µm, and a weaker basal texture. Tensile test results indicated that the extruded MYZCA alloy exhibited the excellent strength-ductility synergy, whose yield strength, ultimate tensile strength, and elongation at fracture were 309.6 MPa, 398.5 MPa, and 22.2%, respectively. The high tensile strengths at room temperature were primarily attributed to grain refinement and secondary phase strengthening, while the good ductility was mainly owing to texture weakening and the activation of non-basal dislocations.

Keywords

extruded Mg-Y-Zn-Co-Al alloy / long period stacking order (LPSO) phase / microstructure / mechanical properties

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