Effect of Quenching Temperature on Age Hardening of AA6016 Sheets
Heat treatable AlMgSi alloys are being used increasingly for automotive skin sheet. AA6016 sheets produced from direct chill (DC) cast ingots are the material of choice in Europe. However, manufacturing of sheets using twin-roll casting (TRC) is a cost effective alternative to DC casting. The effect of processing parameters on the age hardening of TRC AA6016 sheets was assessed. The influence of quenching temperature after solution annealing and subsequent pre-aging at 100 °C was studied. Sheets in the artificially aged condition were prepared using a simulated car-body paint baking procedure (180 °C/30 min). The precipitation kinetics, resulting dispersion of the agehardening phase and their correlations with properties were investigated by differential scanning calorimetry, transmission electron microscopy and tensile tests. It is demonstrated that pre-aging results in increased age hardening effect, especially in the material quenched to 20 °C after solution annealing. The differences in strength are ascribed to the differences in the nucleation rate of β'' precipitates during stabilisation and the formation of stable GP-I zones in naturally aged specimen. The differences in precipitate microstructure inherited from the pre-treatment affect precipitation kinetics during paint baking and result in different precipitate dispersion and sheet strength.
M. Slámová et al., "Effect of Quenching Temperature on Age Hardening of AA6016 Sheets", Materials Science Forum, Vols. 567-568, pp. 333-336, 2008