Achieving superior elevated-temperature strength of Mg-12Gd-3Y alloys by Nd addition

There is a tremendous demand for heat-resistant Mg alloys in aerospace and automotive applications. In this paper, different Nd contents are added to Mg-12Gd-3Y alloy to design the joint action of multiple rare earth (RE) elements to improve the elevated-temperature (ET) strength. The Mg-12Gd-3Y-1.0Nd alloy after extrusion and aging (E-A) process showed excellent strength and toughness matching at room temperature (RT), 200 °C, and 250 °C. The E-Aed Mg-12Gd-3Y-1.0Nd alloy showed ultimate tensile strength (UTS), tensile yield strength (TYS), and elongation (EL) of 440 MPa, 312 MPa, and 6.2% at RT. The E-Aed Mg-12Gd-3Y-1.0Nd alloy showed UTS, TYS, and EL of 405 MPa, 306 MPa, and 12.6% at 200 °C. The E-Aed Mg-12Gd-3Y-1.0Nd alloy showed UTS, TYS, and EL of 382 MPa, 303 MPa, and 19.4% at 250 °C. The addition of Nd elements reduces the solid solubility of Gd, and Y in the Mg matrix, thus precipitating many Mg5RE and β′ phases in the alloy. The excellent mechanical properties of Mg-12Gd-3Y-1.0Nd alloy after E-A treatment come from the fine grain size, segregation at grain boundaries (GBs), and delicate dispersed second phases. The fine grain size is beneficial to inhibit crack expansion, allowing it to consume more energy during the expansion process and improve strength. Both grain boundary segregation and diffusely distributed second phase can effectively inhibit grain boundary sliding and enhance strength.