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High-resolution 2D and 3D electron microscopy have been employed to investigate the dealloying of S phase (Al 2 CuMg) particles in an AA 2024-T3 aluminium alloy. Preferential dissolution of magnesium and aluminium produced a sponge-like remnant with nanosize porosity and a copper-rich remnant network. The dealloyed S phase remnant retains a tetragonal structure with a smaller lattice parameter than the S phase. Metallic copper nanoparticles, constituting 4–8% of the dealloyed remnant, are present at the intersections of remnant branches. At the surface of the remnant, a copper layer of ∼2 nm thickness is formed, which terminates further dissolution of the less noble elements. [ABSTRACT FROM AUTHOR]