Evolutions of Microstructure and Mechanical Properties in Mg-5Li-1Zn-0.5Ag-0.5Zr-xGd Alloy

The evolution of the microstructure and mechanical properties of alloy system with nominally composition Mg-5Li-1Zn-0.5Ag-0.5Zr-xGd (x = 0, 1.2, 2.4, 3.6, 4.8, 6) is evaluated based on computational phase diagram and corresponding experimental studies. The results show that grains are significantly refined with the increase of Gd content. The main phases of as-cast alloys are alpha-Mg, beta-Li, AgLi2Mg, and Mg3Gd. With the increase of Gd content, the amounts of Mg3Gd phase and beta-Li phase have been increased. When the Gd content exceeds 3.6 wt%, Mg3Gd phase precipitates in a form of the network at the grain boundaries. The precipitation of beta-Li can be attributed to the competitive dissolution of Zn, Gd, and Li in Mg. Meanwhile, gamma & DPRIME; is formed after the addition of Gd, which grows and transforms into gamma & PRIME; with the increase of Gd content. In solidification process, stacking faults are formed by solid transformation of partial alpha-Mg and Mg3Gd. Eventually, with the synergistic effect of Mg3Gd, beta-Li, and gamma & DPRIME; (or gamma & PRIME;), as the Gd content increasing, the tensile strength of the alloy first increases, then decreases, and the elongation decreases. When the content of Gd is 4.8 wt%, the ultimate tensile strength and yield strength reach the maximum values of 227 MPa and 139 MPa, and the elongation is 18.1%, respectively.

Automated summary

The evolution of the microstructure and mechanical properties of the alloy system with different Gd content was evaluated. The results show that grains are refined with the increase of Gd content. The main phases are alpha-Mg, beta-Li, AgLi2Mg, and Mg3Gd. The tensile strength first increases and then decreases with the increase of Gd content, reaching a maximum at 4.8 wt% Gd.