Improved Corrosion Resistance of a Dual-Phase Mg-Li-Al-Zn Alloy via Partial Zn Substitution with Gd

Zn was partially substituted with Gd in a dual-phase Mg-Li-Al-Zn (LAZ) alloy, aiming to further reduce the density of these ultra-light materials. The effects of Gd addition (LAZ-Gd) and subsequent annealing treatment (LAZ-Gd-T) on the microstructural evolution and corrosion behavior of the alloys were investigated. The Gd-containing alloys exhibited a lower density of 1.50 g·cm -3 compared to the baseline LAZ alloy (1.52 g·cm -3 ). Microstructural analysis showed that the LAZ alloy consists of a β -Li + α -Mg dual-phase along with significant amounts of secondary (Al,Zn)Li and (Li,Mg) 3 (Al,Zn) phases. Partial substitution of Zn with Gd suppressed the formation of (Al,Zn)Li and (Li,Mg) 3 (Al,Zn) phases, while promoting the precipitation of the Al 2 Gd intermetallics. Fine (Li,Mg) 3 (Al,Zn) and coarser (Al,Zn)Li phases re-precipitated in LAZ-Gd-T, which mitigated galvanic corrosion activity. The LAZ-Gd alloy developed a more protective corrosion film, attributed to a higher aluminum oxide content and a distribution of Gd oxides within the corrosion layer. Therefore, Gd alloying reduced the corrosion rate of the LAZ alloy from 2.55 mm/y to 0.63 mm/y (LAZ-Gd). Annealing slightly increased the corrosion rate to 1.29 mm/y in the LAZ-Gd-T condition. This work provides valuable insights into designing lighter Mg-Li based alloys with simultaneously enhanced corrosion resistance.