Effect of Zr Addition on Overaging and Tensile Behavior of 2618 Aluminum Alloy

The effect of Zr addition on overaging and tensile behavior in a 2618 Al-Cu-Mg-Ni-Fe alloy has been investigated in this study. The chemical composition of the base 2618 alloy, containing similar to 0.1 wt % of Zr, was modified by adding Zr to reach the target content of 0.25 wt %. Cast bars were T6 heat-treated according to industrial parameters, involving soaking at 525 degrees C for 8 h, quenching in hot water (50 degrees C), and artificial aging at 200 degrees C for 20 h. Both the T6 2618 and 2618 + Zr alloys were overaged at 250 and 300 degrees C for up to 192 h, to evaluate the decrease in hardness with high temperature exposure time. The tensile behavior of the alloys was investigated in the overaged condition, both at room temperature and at 250 degrees C. The microstructure of the as-cast and solution-treated samples was investigated by optical and scanning electron microscopy, while the precipitate microstructure at the nanoscale was analyzed by transmission electron microscopy in overaged condition. Experimental data revealed that the presence of 0.25 wt % Zr does not induce modifications at the macroscale on the microstructure of 2618 alloy while, at the nanoscale, the presence of Zr-based precipitates was observed. The overaged Zr-enriched alloy showed increased yield and ultimate tensile strength in comparison to the base alloy, at equal heat treatment condition, both at room temperature and 250 degrees C