Assessment of the Microstructural Evolution of Naturally Aged Open-Cell Al-1.96Cu (at.%) Foams

Open-cell Al-1.96Cu (at.%) foams were produced by the replication casting technique in a 2.00–2.38 mm cell size. The produced foams were solution-treated at 535 °C for 5.5 h. Afterward, natural aging occurred at room temperature for 12, 24, and 36 months, and as a reference artificial aging at 170 °C for 8 h was also reported. The microstructural evolution of the studied samples was assessed through X-ray diffraction, the Rietveld refinement technique, and transmission electron microscopy. In addition, Vickers microhardness tests were carried out for all testing conditions. It was found that the lattice parameter of the supersaturated α-Al phase increased progressively with the natural aging at room temperature, which was attributed to the diffusion from the solid solution of the initially supersaturating Cu atoms toward Guinier–Preston zones and Cu-rich precipitates, thereby relaxing the Al lattice. In addition, it was demonstrated that the microstructure after natural and artificial aging is different.