Abstract
The evolution of precipitate microstructures of the Al-1.0wt%Cu-2.5wt%Li alloys with different micro-alloyed elements addition was investigated during ageing at 175 °C together with the mechanical properties and corrosion resistance. It was found that the Al-Cu-Li alloy with Zn addition possesses not only higher yield strength but also improved intergranular corrosion resistance, compared with the alloy with Mg addition. The corresponding precipitate microstructures were greatly affected by Zn or Mg micro-alloyed element addition, for example, with Zn addition the δ′-Al3Li, T1-Al2CuLi and θ′-Al2Cu (and θ″) phases were formed within grains, whereas the coarse TB-Al7Cu4Li phase and the T1 phases appeared at grain boundaries (GBs). In contrast, the Al-Cu-Li alloy with Mg addition possessed the δ′, T1 and S′-Al2CuMg phases within grains, while the coarse AlCu phase and T1 phases were present at GBs. The alloy with combined Zn + Mg addition exhibited a duplex microstructure of the two alloys, resulting in lower mechanical strengths but the intermediate corrosion resistance. Therefore, the increased amount of Zn-containing coarsened TB phase at GBs was found to improve the corrosion resistance of the alloy with Zn addition, due to the smaller potential difference between the GB precipitates and the adjacent zones.
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