Investigation on the microstructural evolution and corrosion behaviors of Zn-microalloyed Al-Cu-Li alloys

Zn microalloying made great contributions to microstructures evolution and performances enhancement. The effects of various contents of Zn on the precipitate microstructure, tensile property and corrosion behavior of Al3.2Cu-1.5Li alloys with medium Cu/Li mass ratio were examined by tensile testing and corrosion measurement. Experimental results demonstrated that the tensile strength of the Zn microalloyed samples dropped slightly as the Zn content increased due to the number density of precipitates with minor size variation showed a downward trend within the grains. Corrosion testing revealed that the corrosion type of Zn microalloyed samples was primarily localized intragranular corrosion, slight intergranular corrosion and local pitting corrosion was also partially involved. The emergence of Zn element in grain boundary (GB) coarse (T1) phases and the suppressed precipitation of intragranular phases in the alloys with higher content Zn were found to reduce corrosion sensitivity with the increase of Zn content, which was ascribed to the decreased potential difference between the GB and adjacent matrix, and between the GB precipitates and precipitation free zone (PFZ).