Solidification Behavior of Mg-Zn and Mg-Zn-Zr Alloys Using In-Situ Neutron Diffraction

In-situ neutron diffraction was used to examine the solidification behaviors of Mg-Zn and Mg-Zn-Zr alloys by melting the alloy in a graphite crucible and irradiating the sample using monochromatic neutrons at 25 different temperatures as it solidified and cooled from 650 to 300 °C. The microstructure of the solidified Mg-Zn sample after in-situ neutron diffraction consisted of Zn-enriched Mg matrix and had an average grain size of ~1500 μm. The Mg-Zn-Zr alloy had a grain size of ~240 μm. The coarse grain size of the Mg-Zn alloy resulted in a large variation in neutron-scattering intensities between the \( ( 1 0 {{\bar{1}0)}} \) and \( ( 1 0 {{\bar{1}1)}} \) planes with the \( ( 0 0 0 2 ) \) plane being absent, while the Mg-Zn-Zr alloy had the planes \( ( 1 0 {{\bar{1}0)}} \), \( ( 1 0 {{\bar{1}1)}} \), and \( ( 0 0 0 2 ) \) which are all clearly represented. The authors determined that finer grain sizes improved counting statistics and that increasing sample dimensions or sample oscillation could further improve the diffraction results.