Li-ALLOYED Mg–Zn–Ca Systems’ Phase Structure Modification, Mechanical Properties and Corrosion Performance

Abstract Magnesium–lithium (Mg–Li) binary alloys have attracted significant attention in recent years due to their exceptionally low density and high specific strength. Lithium, with a density of 0.58 g/cm 3 , is lighter than magnesium, making Mg–Li alloys highly attractive for aerospace, defense, and additive manufacturing applications where weight reduction is critical. The mechanical properties of Mg–Li alloys are strongly dependent on their crystal structure, which varies with lithium content and can exist in hexagonal close-packed (HCP), body-centered cubic (BCC), or dual-phase (HCP + BCC) forms. Additional alloying with calcium (Ca) and zinc (Zn), either individually or in combination, can further enhance mechanical performance. In the present study, three Mg–Li–Zn–Ca alloys—LZX110, LZX420, and LZX920—were produced via permanent mold casting following ASTM standards, with fixed Zn and Ca contents. LZX110 consisted solely of the α-Mg(Li) HCP phase, while LZX920 was composed entirely of the β-Li(Mg) BCC phase. X-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM–EDS) analyses revealed that LZX420 exhibited a dual-phase structure containing both α-Mg(Li) and β-Li(Mg) phases. Zn and Ca were found to dissolve within the matrix phases, contributing to solid solution strengthening without forming distinct secondary phases. Hardness increased with Li content, with average values of 50.92 HV, 66.68 HV, and 73.56 HV for LZX110, LZX420, and LZX920, respectively. LZX920 exhibited the highest yield strength (195 MPa) and ultimate tensile strength (196 MPa), whereas LZX420 demonstrated the greatest ductility (13.5%). Overall, the dual-phase LZX420 alloy provided an optimal balance of strength and ductility, making it a promising candidate for lightweight structural applications.