Microstructure and mechanical properties of extruded and rolled Mg–Y–Zn–Ni–Co alloy

Abstract

The as-cast Mg–2Y-0.5Zn-0.5Ni-0.5Co alloy (MYZNC, at%) underwent composite hot working, extrusion and rolling to further improve the mechanical properties, and the corresponding microstructure and mechanical properties were also investigated. The extruded and rolled MYZNC alloy (MYZNC-R) consisted of α-Mg, a long period stacking order (LPSO) phase comprising lamellar and fine block 18R LPSO phase as well as a thin strip 14H LPSO phase, along small amounts of Mg2Y, MgY(Co,Zn,Ni)4 and Mg3(Co,Zn,Ni,Y) particle phases. After composite processing, the dispersion and amounts of LPSO phase in the alloy was significantly enhanced, accompanied by a substantial introduction of low angle grain boundaries (LAGBs) during rolling process. The MYZNC-R alloy exhibited the high mechanical properties, with an ultimate tensile strength (σb) of 350 MPa, a yield strength (σ0.2) of 305 MPa and an elongation to failure (εf) of 10.6 %. In comparison to the extruded MYZNC alloy, both σb and σ0.2 demonstrated significant improvements by 25 % and 35.6 %, respectively. The elongation to failure only decreased by mere 1 %, indicating that the alloy had a good strength-plasticity. The high tensile strengths of MYZNC-R alloy were mainly attributed to grain refinement, LPSO phase strengthening and texture strengthening. The good ductility of MYZNC-R alloy was associated with the coordinated deformed LPSO phase and the formation of a high-volume fraction (∼76.5 %) of LAGBs.

Keywords

• Extruded and rolled Mg–Y–Zn–Ni–Co alloy
• Mechanical properties
• LPSO phase
• Low angle grain boundary