Precipitation in 339 and 2124 aluminum: A caveat for calorimetry

The sequence of precipitation in solutionized (SOL) 2124 aluminum and direct-quenched from the die (DQD) 339 aluminum has been identified by a combination of differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Both alloys form S' (Al2CuMg) as the first precipitate after GP zone dissolution. In each alloy a second phase forms at higher temperatures—Si for DQD 339 Al, θ′ (CuAl2) for SOL 2124 Al. These results …