H. Choo, Z. Yu, University of Tennessee, Knoxville, TN
A series of compression tests was conducted for AZ31B magnesium alloy at temperatures ranging from 350°C to 500°C and strain rates between 10-3 and 10 s-1 to establish a constitutive relationship among the deformation mechanisms, grain refinement, and Zener-Hollomon parameter (Z) as a function of the initial grain size. Two dynamic recrystallization (DRX) processes corresponding to different deformation mechanisms were identified under the current experimental conditions. At lower temperatures and higher strain rates, when Z is greater than 1×1014 s-1, the dominant mechanism is discontinuous DRX. As Z parameter decreases, twins are observed in declining numbers, and more DRX grains start to originate at grain boundaries instead of at the twin boundaries. As Z decreases below 1×1013 s-1 under higher temperatures and lower strain rates, DRX mechanism changes to a continuous process and final microstructure was more homogeneous and exhibited equiaxed grain structure. Furthermore, the influence of initial grain size was considered in the Z-d relationship. Finally, the dependence of the final grain size on Z parameter was compared to the relationship between the grain sizes and welding parameters in the stir zone (SZ) of friction stir welded (FSW) AZ31B plates. The comparison shows a good agreement implying that the current study may be useful in predicting the deformation mechanisms, peak temperatures, and microstructures in the SZ based on the FSW parameters.
Summary: A series of compression tests was conducted for AZ31B magnesium alloy at temperatures ranging from 350°C to 500°C and strain rates between 10-3 and 10 s-1 to establish a constitutive relationship among the deformation mechanisms, grain refinement, and Zener-Hollomon parameter (Z) as a function of the initial grain size. Two dynamic recrystallization (DRX) processes corresponding to different deformation mechanisms were identified under the current experimental conditions.
