Effect of Cu content on mechanical and intergranular corrosion properties of Al-Cu-Mg-Ag alloy

The differences in the microstructure, mechanical properties, and intergranular corrosion performance of three Al-Cu-Mg-Ag alloys with varying Cu content were analyzed. The results show that Cu content primarily affects the precipitation of intragranular Ω and S′ phases, as well as the type and distribution of grain boundary precipitates (GBPs). As the amount of Cu increases, the diameter and volume fraction of the Ω phase increase, while the proportion of the S′ phase first increases and then decreases. The alloy with high Cu content exhibits higher strength, mainly due to a larger contribution from precipitate strengthening (mainly the Ω phase) and strengthening provided by additional Cu atoms. However, the lower number density of the Ω phase results in poor fatigue resistance. The GBPs transition from the intermittently distributed S phase to the continuously distributed S and θ phases, which is the main reason for the decrease of intergranular corrosion resistance in high Cu alloys and also has some impact on the fatigue resistance of the alloy. Electrochemical characteristics also show that high Cu alloys have higher free corrosion current density and corrosion rate, lower polarization resistance, and smaller charge transfer resistance of the double layer and inductance values.