Effects of yttrium additions on microstructures and mechanical properties of cast Al-Cu-Mg-Ag alloys

The effects of microalloying with yttrium on the microstructures and mechanical properties of cast Al-Cu-Mg-Ag alloys at ambient and elevated temperatures are investigated using tensile testing, differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The present results reveal that the strength properties of peak-aged Al-Cu-Mg-Ag alloys at 300 °C are considerably improved with the additions of Y. Al8Cu4Y phase is found to segregate at the localized regions along grain boundaries and strengthens the grain boundaries at elevated temperature. However, the Ω precipitation is gradually suppressed by Y additions, thereby degrading the strength of Al-Cu-Mg-Ag alloys at ambient temperature. This negative effect of Y is directly associated with the formation of blocky (Cd, Ag, Ti, V, Y)-rich intermetallics, which consumes the available Ag atoms for Ω nucleation and hence leads to the lower number density of Ω plates.