Effect of Initial Grain Size on Dynamically Recrystallized Grain Size in AZ31 Magnesium Alloy

The effect of initial grain size on dynamically recrystallized grain size (DRX grain size) is examined in AZ31 magnesium alloy with four kinds of initial grain sizes. When the average grain size after the high-temperature compression test is plotted against Zenner-Hollomon parameter (Z-parameter), initial grain size dependence on DRX grain size appears only in the specimen with large initial grain size in the low Z region, but not in the specimen with small grain size or in high Z region. When the grain size measured only in recrystallized region is plotted against Z-parameter, initial grain size dependence on DRX grain size does not appear. From these results, it is concluded that there is no initial grain size dependence on DRX grain size when the DRX proceeds to some degree, because the DRX grain size becomes constant for a given Zvalue. The initial grain size dependence on DRX grain size observed in the low Z region would be related to the rotation of basal plane perpendicular to the compression axis during deformation before the DRX grains have been developed sufficiently

Fabrication of Ti-Alloy powder/solid composite with uniaxial anisotropy by introducing unidirectional honeycomb structure via electron beam powder bed fusion

In this study, a Ti–6Al–4V alloy composite with uniaxial anisotropy and a hierarchical structure is fabricated using electron beam powder bed fusion, one of the additive manufacturing techniques that enable arbitrary fabrication, and subsequent heat treatment. The uniaxial anisotropic deformation behavior and mechanical properties such as Young’s modulus are obtained by introducing a unidirectional honeycomb structure. The main feature of this structure is that the unmelted powder retained in the pores of the honeycomb structure. After appropriate heat treatment at 1020◦C, necks are formed between the powder particles and between the powder particles and the honeycomb wall, enabling a stress transmission through the necks when the composite is loaded. This means that the powder part has been mechanically functionalized by the neck formation. As a result, a plateau region appears in the stress–strain curve. The stress transfer among the powder particles leads to the cooperative deformation of the composites, contributing to the excellent energy absorption capacity. Therefore, it is expected that the composite can be applied to bone plates on uniaxially oriented microstructures such as long bones owing to its excellent energy absorption capacity and low elasticity to unidirectionally suppress stress shielding.Ikeo N., Matsumi T., Ishimoto T., et al. Fabrication of Ti-Alloy powder/solid composite with uniaxial anisotropy by introducing unidirectional honeycomb structure via electron beam powder bed fusion. Crystals, 11, 9, 1074. https://doi.org/10.3390/cryst11091074

Experimental Investigation of Cavitation Behavior in AZ61 Magnesium Alloy

The rate of cavitation with superplastic strain was investigated for a superplastic AZ61 magnesium alloy at a strain rate of 2 Â 10 À4 s À1 and temperature of 648 K, under the conditions of which an elongation of more than 250% has been found. Cavities initiated at grain boundaries. The cavitation showed a growth perpendicular to the applied stress direction after the initial strains. The subsequent growth and coalescence of cavities invariably leads to failure of the material. The experimental growth rates are in good agreement with the rate predicted by the plasticitycontrolled growth mechanism