Precipitation enthalpy during cooling of aluminum alloys obtained from calorimetric reheating experiments

Precipitation reactions inside aluminum alloys are known to be very important for hardness and yield strength. Premature precipitation during quenching from solution annealing decreases the yield strength after aging. A methodology to determine the amount of precipitates as a function of quench rate (quench sensitivity) for a wide range of aluminum alloys from calorimetric reheating scans is proposed. The method allows determining the critical cooling rate for suppressing precipitation during quenching. Differential fast-scanning calorimetry was applied to cover the cooling rate range needed for high alloyed materials. The critical cooling rate for the quench sensitive EN AW 7049A alloy was determined as 300 K/s. A new methodology, called differential reheating method, was applied for differential fast-scanning calorimetry (DFSC) and differential scanning calorimetry (DSC). The method was quantitatively verified with EN AW 6063 alloy in a DSC due to its low critical cooling rate. The combination of DSC and DFSC extends the available cooling rate range for precipitation studies from mK/s up to some 10,000 K/s. (C) 2011 Elsevier B.V. All rights reserved.