Quench sensitivity of Al–Cu–Mg alloy thick plate

The quench sensitivity of Al–Cu–Mg alloy was investigated at different thicknesses of the thick plate. The quenching process was simulated via finite element analysis (FEA); time–temperature–property (TTP) curves and time–temperature–transformation (TTT) curves were obtained through hardness test and differential scanning calorimetry (DSC) test; and the microstructural observation was carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Experimental results exhibit that the quench cooling rate decreases dramatically from the surface to the center of the plate, and the inhomogeneous quenching causes the difference in microstructure. With the decrease in quench cooling rate, constituent particles are coarsening gradually; the quantity of T-phase (Al₂₀Cu₂Mn₃) increases and the S-phase (Al₂CuMg) decreases. According to the precipitation kinetics analysis, the decrease in S-phase is caused by the increase in precipitate activation energy. So that the center of the plate shows the highest quenching sensitivity, which is consistent with the analysis of time–temperature–property curves and time–temperature–transformation curves.