Effect of the volume fraction of the icosahedral phase on the microstructures, hot compressive behaviors and processing maps of Mg-Zn-Y alloys

• Published in: Journal of alloys and compounds Vol. 725; pp. 711 - 723
• Main Authors: Kwak, T.Y., Lim, H.K., Kim, W.J.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25-11-2017; Elsevier BV
• Subjects: Alloys; Concentration (composition); Deformation mechanisms; Dynamic recrystallization; Eutectics; Flow stability; Grains; Hot workability; Icosahedral phase; Lamellar structure; Liquid-solid reactions; Magnesium base alloys; Mechanical properties; Metals and alloys; Microstructure; Nuclear electric power generation; Nucleation; Quasicrystals; Recrystallization; Solid phases; Strain rate; Studies; Workability; Yttrium; Zinc base alloys; Mechanical properties; Liquid-solid reactions; Metals and alloys; Microstructure; Quasicrystals
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.07.164

The effect of the volume fraction (0.6–8.4 vol %) of the icosahedral phase (I-phase, Mg3Zn6Y1) on the microstructure, hot deformation mechanism and hot workability of cast Mg-Y-Zn alloys was studied. As the volume fraction of I-phase increased, the fraction of dynamically recrystallized (DRXed) grains increased, indicating that I-phase promoted dynamic recrystallization (DRX) by providing the preferred nucleation sites for DRXed grains through particle stimulated nucleation mechanism. There was, however, a critical amount of I-phase (about 5 vol %) beyond which the fraction of DRXed grains decreased. This was attributed to the formation of relatively coarse divorced eutectic I-phase and lamellar I-phase structures at the volume fraction of I-phase ≥5%. This result indicates that besides the amount of I-phase, the size of I-phase structure is another important factor affecting DRX. Processing maps were constructured to evaluate the hot workability of the alloys with different volume fraction of I-phase. The hot workability increased as the volume fraction of I-phase increased up to about 5 vol % but decreased afterward, confirming that DRX and hot workability are correlated with each other. The hot workability increases with increasing I-phase amount because the occurrence of extensive DRX delays the onset of power-law breakdown and flow instability to higher strain rates and lower temperatures.
•The effect of the amount of I-phase on the hot deformation behavior was examined.•The I-phase promotes dynamic recrystallization (DRX).•There is an optimum amount of I-phase for the highest extent of DRX.•The I-phase suppresses the formation of shear bands at high strain rates.•The benefit of more I-phase on DRX is more pronounced at high strain rates.