Effects of semisolid treatment and ECAP on the microstructure and mechanical properties of Mg-6.52Zn-0.95Y alloy with icosahedral phase

The microstructure evolutions and mechanical properties of Mg-6.52Zn-0.95Y (wt%) alloy with icosahedral phase (I-phase) by semisolid treatment and equal channel angular processing (ECAP) were systematically investigated. After semisolid treatment, lamellar ultra-fine eutectic phases with spacing of 100 +/- 19 nm formed at the grain boundaries. After subsequent 4 passes ECAP, fine grains (2.9 +/- 0.4 gm) were obtained and the lamellar eutectic phases were fragmented into 50-500 nm granular particles. The best comprehensive mechanical properties with ultimate tensile strength (UTS) of 385 +/- 18 MPa, tensile yield strength (TYS) of 290 +/- 3 MPa and elongation to failure (EL) of 22.0 +/- 1.6% were obtained by the combination of semisolid treatment and subsequent 2 passes ECAP at 300 degrees C followed by 2 passes ECAP at 200 degrees C, compared with that by the initial alloy. The improvement of mechanical properties results from combined effects of the grain refinement, dispersion of nanoscale I-phase particles and weakened basal texture. In addition, the I-phase particles contributed to the grain refinement during dynamic recrystallization by particle stimulated nucleation (PSN), which contributed to both strength and ductility. The average Schmid factor (SF) of basal slip increased from 0.2 to 0.4 after semisolid treatment and ECAP processing, which benefit the ductility.