Correlation of Crystal Orientation, Crystal Morphology and Mechanical Properties of Directionally Solidified Mg-xGd Alloys

The Mg-xGd (x = 4–16, wt%) alloys with columnar crystals were prepared by directional solidification, and the effect of Gd content on the crystal orientation, microstructure, and tensile properties at room temperature were studied. The microstructure of the Mg-4Gd alloy is single α-Mg solid solution, and the microstructure of the Mg-6Gd alloy is composed of α-Mg and Mg24Gd distributed along the longitudinal grain boundaries of columnar crystals, while the microstructure of the Mg-(8−16)Gd alloys consists of α-Mg and lamellar eutectic phase. The Mg-4Gd alloy with growth orientation concentrated in< 112(_)0 > (hard orientation) has high yield strength (186 MPa) and moderate elongation (12 %), because {101(_)1} compression twinning are activated to coordinate strain. However, the Mg-6Gd alloy with growth orientation concentrated in<1(_)21(_)2 > (soft orientation) has excellent elongation (38 %), as a result of activated {101(_)2} tension twinning. When the Gd content exceeds 12 %, plenty of eutectic phases will cause low strength and poor plasticity of the Mg-Gd alloys.