Nucleation of Precipitates on Multiple Habit Planes in an Artificially Aged AA2618 Alloy

The aim of this investigation is to study precipitation behavior in an aluminum alloy AA2618, based on Al–Cu–Mg–Si–Ni–Fe system. The as-received extruded alloy was solution treated and independently aged at ambient temperature as well as aged for various times at 193 ± 1 ℃, and at 275 ± 1 ℃ for 5 h. TEM revealed that the microstructure developed due to prolonged natural aging consisted of a fine distribution of Guinier–Preston–Bagaryatski (G-P-B) zones. During artificial aging, the sample aged for as low as 1 h revealed the presence of very fine precipitates on both {220}Al and {420}Al planes. With increasing artificial aging hours, widespread precipitation occurred on both {220}Al planes, and, of course, on {420}Al planes that are known to be due to the S′/S (Al2CuMg) phase. The corresponding selected area diffraction patterns confirmed the presence of G-P-B zones and S phase in the microstructure. Preliminary high-resolution transmission electron microscopy (HRTEM) did confirm the presence of precipitates on {220}Al planes in the artificially aged samples of AA2618.