Synergistic Improvement of Mechanical and Electromagnetic Shielding Properties of a Mg-Li-Y-Zn Alloy Following Heat Treatment

The performances of magnesium alloys remain insufficient to further enhance the application potential of ultralight magnesium alloys. In this work, a Mg-8Li-3Y-2Zn alloy was prepared through vacuum melting and subsequent heat treatment at 300, 450, and 500 °C. The material properties of the resulting samples were assessed through microstructural observation, tensile testing, electrical conductivity measurements, and electromagnetic shielding effectiveness (EMI-SE) testing. The influence of the Mg-8Li-3Y-2Zn alloy microstructure on its mechanical and electromagnetic shielding properties in different states was investigated. It was found that the as-cast alloy contains α-Mg, β-Li, Mg3Zn3Y2, and Mg12ZnY phases. Following heat treatment at 500℃ (HT500), the block α-Mg phase transformed fine needle-shapes, its tensile strength increased to 263.7 MPa, and its elongation reached 45.3%. The mechanical properties of the alloy were significantly improved by the synergistic effects imparted by the needle-shaped α-Mg phase, solid solution strengthening, and precipitation strengthening. The addition of Y and Zn improved the EMI-SE of Mg-8Li-1Zn alloy, wherein the HT500 sample exhibits the highest SE, maintaining a value of 106.7–76.9 dB in the frequency range of 30–4500 MHz; this performance has rarely been reported for electromagnetically shielded alloys. This effect was mainly attributed to the multiple reflections of electromagnetic waves caused by the severe impedance mismatch of the abundant phase boundaries, which were in turn provided by the dual-phase (α/β) and secondary phases. Furthermore, the presence of nano-precipitation was also believed to enhance the absorption of electromagnetic waves.