High-ductility fine-grained Mg-1.92Zn-0.34Y alloy fabricated by semisolid and then hot extrusion

Abstract

The combination of semisolid and hot extrusion processing was applied to refine the icosahedral quasicrystalline phase (I-phase) in an extruded Mg-1.92Zn-0.34Y(wt.%) alloy for the first time. The semisolid isothermal heat treatment transformed the micron-sized I-phase particles into nano lamellar eutectic (α-Mg + I-phase) with a lamellar spacing of ~86 nm. After subsequent hot extrusion at 250 °C, the nano lamellar eutectic phases were broken into uniformly dispersed nanoscale I-phase particles. What's more, the matrix microstructure was significantly refined with an equiaxed average grain size of 2.59 ± 0.81 µm, and an unusual texture component (most of the grains’ c-axis is parallel to the extrusion direction) was observed. The processed alloy exhibited a high tensile elongation to failure (EL) of 44 ± 2.6% with an ultimate tensile strength (UTS) of 258 ± 2.0 MPa and a tensile yield strength (TYS) of 176 ± 1.6 MPa at room temperature. The high ductility from the combined effects of the grain refinement, dispersion of nanoscale I-phase particles, and the unusual texture. The uniform dispersion of nanoscale I-phase particles could promote grain refinement by particle stimulated nucleation mechanism, and thus bring the unusual texture (where the c-axis is aligned parallel to the extrusion direction during dynamic recrystallization, which contributed to ductility).