Effect of High Lithium Content on the Microstructure and Properties of Al-Mg-Si-Mn Casting Alloys

The widespread use of lithium-containing wrought aluminum alloys is attributed to their high mechanical strength combined with reduced density. Currently, Al-Cu-Li and Al-Mg-Li wrought alloys are regarded as promising materials for applications where low density is essential. Despite this, the development of lithium-containing casting aluminum alloys remains limited. In this study, the Al5Mg2SiMn-type alloy was selected as the base material, with lithium additions ranging from 0.8 to 4.0 wt.%. The microstructure of the experimental alloys was characterized using macro- and microstructural analyses, energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction, and mechanical testing to determine hardness and compressive yield strength. The addition of 2.1 wt.% lithium resulted in a complete change of the alloy structure from a fine-lamellar eutectic-type to coarser blocky intermetallics. This trend persisted in alloys with 2.5, 3.0, and 4.0 wt.% Li. The alloy with 4.0 wt.% lithium led to a significant increase in hardness, from 82 HV5 in the base alloy to 157 HV5. Compression tests demonstrated a similar improvement, with yield strength increasing from 135 MPa to 352 MPa in the as-cast condition. Tests conducted at 300 °C showed a gradual increase in yield strength from 124 MPa to 170 MPa at 4.0 wt.% lithium. These results demonstrate the strong potential of lithium-containing Al5Mg2SiMn-type alloys for foundry applications without the need for additional heat treatment.