An Automotive Almgsi Alloy Enhanced by Li-Addition

Abstract

Li-addition is often used in aluminum alloys, e.g., typically in the AlCuLi(Mg) alloy system, in order to further enhance their strength-to-weight ratio. However, little has been known about the effect and mechanism of Li-alloying on the microstructures and properties of automotive AlMgSi(Li) alloys. Using state-of-the-art characterization and testing instruments, here we report the enhanced properties of a Li-added AlMgSi(Li) alloy in relation with its precipitation microstructures, which are significantly modified by Li-addition. It is clearly revealed that during precipitation upon thermal aging, Li-atoms can enter all strengthening phases such as β", U2, and β' phases, as well as their interfaces, and occupy specific Mg sites. Hence, for alloys with a low Mg/Si ratio, Li-addition has the effect of increasing the volume fractions of hardening precipitates and therefore enhances the alloy’s strength. Additionally, calculations indicate that the Li-containing β"Li-phase can be more effective in strengthening the alloys as compared to the β"-phase without Li-content. Our study offers an atomic-scale insight into the enhanced properties of Li-added automotive AlMgSi(Li) alloys in more detailed relations with their microstructures.

Keywords: AlMgSi alloys, Precipitation, Strength, Electron microscopy, Atom probe tomography, Li-addition