Microstructure of AlLiCuMgZr alloys with In additions

The effects of small additions of In on the age-hardening and microstructure of Al-Li-Cu-Mg-Zr alloys are studied. The addition of In significantly increases the peak hardness of the alloys aged at 185°C. Optical metallography, X-ray diffraction, scanning and transmission electron microscopy, electrical resistivity and differential scanning calorimetry were employed in order to study the microstructure and the precipitation kinetics of the alloys. The addition of In seems to modify the δ′ and S′ precipitations, while large In-rich precipitates develop within the grains and mainly at grain boundaries. The alloys containing In show a homogeneous distribution of fine, rod-shaped and still uncharacterised intraganular precipitates.