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 °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, β′ precipitates and tentacle-like structures with specific crystallographic directions around β′ body are the main phases. The crystallographic directions of tentacle-like structures are {112‾0}Mg. When 3Y is added, β′ and β1 precipitates become the main phases. Except that, the size and area number density of β′ precipitate are also influenced by adding Y. With Y addition, the size of β′ 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-Y-0.5Zr alloys are β′ precipitates, and the strengthening effect of the β′ precipitates on the yield strength of the Mg-Gd-(Y)–Zr alloys with low Gd/Y content is more obvious than the Mg-Gd-(Y)–Zr alloys with high Gd/Y content.