Microstructure and mechanical properties of cast Mg-6Gd-Zr alloy with different Y addition

Microstructures and mechanical properties of Mg-6Gd-xY-0.5Zr (wt.%, x = 0, 0.5, 1 and 3) alloys with different conditions (solution-treated and 200 degrees C peak-aged) are investigated. Species of precipitates in Mg-6Gd-0.5Zr alloys are modified by Y addition. In 0Y, 0.5Y and 1Y alloys, beta ' precipitates and tentacle-like structures with specific crystallographic directions around beta ' body are the main phases. The crystallographic directions of tentacle-like structures are {1120}Mg. When 3Y is added, beta ' and beta 1 precipitates become the main phases. Except that, the size and area number density of beta ' precipitate are also influenced by adding Y. With Y addition, the size of beta ' precipitate is refined, and its area number density increases. This phenomenon has been explained by theoretical method in this paper. According to the study, Mg-6Gd-1Y-0.5Zr alloy with good combination properties is developed. The yield strength, ultimate tensile strength and elongation of Mg-6Gd-1Y-0.5Zr alloy are 164.4 MPa, 280.6 MPa and 16.1 %, respectively. The strengthening precipitates in the peak-aged Mg-6Gd-Y0.5Zr alloys are beta ' precipitates, and the strengthening effect of the beta ' precipitates on the yield strength of the MgGd-(Y)-Zr alloys with low Gd/Y content is more obvious than the Mg-Gd-(Y)-Zr alloys with high Gd/Y content.