Effects of Rare-earth Y Doping on the High-temperature Plastic Flow Behavior of As-cast ZK30 Magnesium Alloy

In order to improve the understanding of the effect mechanism of rare earth yttrium (Y) element on the plastic deformation of as-cast ZK30 magnesium alloy, and to use it more effectively, we carried out a series of isothermal compressive tests of specimens in the deformation temperature range of 573 similar to 723 K, and the strain rate range of 0.001 similar to 1 s(-1) on thermo-mechanical simulator. Combined with the microstructure observation; the effects of Y (1.5 wt%) on the microstructure, flow behavior, constitutive parameters and high temperature plastic properties of the ZK30 magnesium alloy were investigated. According to the hyperbolic function, constitutive parameters of the alloy were obtained by linear fitting, a nonlinear flow model and its constitutive equation have been established and employed for studying the plastic deformation behavior and the relationship between temperature, strain rate and flow stress. The results show that Y could refine the as-cast grain and increase the amount of eutectic intermetallic compound in grain boundaries. The Y doping could also effectively enhance the flow stress level and peak stress, but the change trend of true stress-strain curves are less affected. The average activation energy (Q=181.082 kJ.mol(-1)) and stress exponent (n = 5.778) for the plastic deformation have been determined, enlarged by 21.6% and 14.2%, respectively. The plastic deformation resistance of the alloy is enhanced. Combined with metallurgy microstructure of these samples after deformation, Y could refine the grains and increase the amount of the dynamic recrystallization in triangle boundaries. Y facilitates the dynamic recrystallization, and it influences the mechanism of interface migration.