Hot compression characteristics and processing maps of a cast Mg–9.5Zn–2.0Y alloy with icosahedral quasicrystalline phase

Abstract

Hot compressive characteristics and processing maps of a cast Mg–9.5Zn–2.0Y alloy with I-phase (ZW92) were studied in the temperature range between 523 and 723K and in the strain rate range between 10−3 and 10s−1. According to the analysis of deformation behavior, the rate-controlling mechanism governing deformation during entire compression process was lattice diffusion controlled dislocation climb creep and power-law breakdown. Comparison of the processing maps of ZW92 with those of the cast Mg–Zn–Y alloys with different types of intermetallic compounds (W- and long period stacking ordered phases) and the cast Mg–Al–Zn alloy (AZ80) alloy with β-Mg17Al12 phase in terms of η values and the domain sizes of the unstable regime indicated that ZW92 exhibited a better hot workability at high strain rates above 1s−1. This result was attributed to the suppression of power law breakdown in ZW92 due to occurrence of extensive dynamic recrystallization at high strain rates, which was facilitated by the effective fragmentation and dispersion of I-phase during deformation at high strain rates. A fully recrystallized microstructure composed of defect-free fine grains (9.34μm) with high fraction of high angle grain boundaries (0.81) was obtained at 623K – 10s−1.