Correlation between microstructure and mechanical properties of columnar crystals in the directionally solidified Mg-Gd-Y-Er alloy

Abstract

The Mg-4.58Gd-0.45Y-0.01Er alloys with different volume fractions of columnar crystals in hard orientation (orientation factor of basal plane slip system is less than 0.2) were prepared by changing the pulling rate to regulate the crystal growth orientation. Tensile tests were performed on the Mg-4.58Gd-0.45Y-0.01Er alloy at room temperature, and the structure after deformation was investigated by electron backscatter diffraction (EBSD). Subsequently, the strengthening mechanism of columnar crystals in hard orientation was explored. The results show if orientation factors of basal plane slip system of columnar crystals are all greater than 0.4 (soft orientation), the alloy has low yield strength σs (64 MPa), but great work hardening ability, and ultimate tensile strength σb and elongation δ are 114 MPa and 37.3%, respectively. If orientation factors of basal plane slip system of columnar crystals are all less than 0.2 (hard orientation), the alloy has high strength (σs, 125 MPa), but poor plasticity (δ, 6.32%). If the “hard orientation” and the “soft orientation” columnar crystals are arranged alternately along the direction perpendicular to the crystal growth, the alloy has both superior strength (σs, 102 MPa) and excellent plasticity (δ, 22.5%) at room temperature. The improved comprehensive mechanical property can be attributed to two factors. On the one hand, the “hard orientation” columnar crystals can prevent the “soft orientation” crystals deforming, so the strength is improved. On the other hand, the “hard orientation” columnar crystals themselves can withstand a certain amount of deformation to retain appropriate plasticity.

Keywords

• Directional solidification
• Mg-Gd-Y-Er alloy
• Hard orientation
• Mechanical properties