(Y, Gd) phase formation in as-cast Mg-6Gd-3Y-0.5Zr alloy

• Published in: China foundry 2021-05, Vol.18 (3), p.217
• Main Authors: Wang, Fei, Fu, Bin-guo, Wang, Yu-feng, Dong, Tian-shun, Li, Guo-lu, Zhao, Xue-bo, Liu, Jin-hai, Zhang, Gui-xian
• Format: Article
• Language: English
• Subjects: Alloys; Analysis; Hydrogen; Specialty metals industry; Thermodynamics; Zirconium
• ISSN: 1672-6421
• DOI: 10.1007/s41230-021-1013-y

In this work, a new (Y, Gd)[H.sub.2] precipitate was identified and systematically investigated in the as-cast Mg-6Gd-3Y-0.5Zr alloy by XRD, SEM with EDS, TEM with EDS techniques and thermodynamics analysis. Results show that the as-cast alloy contains [alpha]-Mg, [Mg.sub.24][(Gd, Y).sub.5], and (Y, Gd)[H.sub.2] phase. The (Y, Gd)[H.sub.2] phase usually forms near the eutectic phase [Mg.sub.24][(Gd, Y).sub.5] or in the [alpha]-Mg grains, displaying a rectangle-shape. The [Mg.sub.24][(Gd, Y).sub.5] and (Y, Gd)[H.sub.2] phases crystalize in bcc and fcc structure, respectively, and the (Y, Gd)[H.sub.2] phase has a semi-coherent relationship with [alpha]-Mg matrix. The thermodynamics calculation results reveal that the hydrogen dissolved in the melt leads to the formation of hydrides. It is also found that the (Y, Gd)[H.sub.2] hydride can form directly from the liquid phase during solidification. Additionally, it can precipitate by the decomposition of [Mg.sub.24][(Gd, Y).sub.5] phase due to absorbing hydrogen from the remaining melt.