抄録
The effect of Ag on the precipitation processes in Al–Mg–Si alloys has been investigated by the specific heat measurement.
In the specific heat versus temperature curve of the quenched Al-1.0wt% Mg2Si alloy, the heat evolutions due to the formation of the ordered G. P. zones (β″) and the intermediate phase β′, the heat evolution due to the transformation β′- the stable phase β and the heat absorption due to the dissolution of β into the matrix were found respectively. The addition of 0.1wt% Ag increased the temperature for the dissolution of β into the matrix, suggesting that the degree of the supersaturation of solute atoms in the matrix is increased. It was also shown that the specific heat curves of specimens with Ag aged at 100° and 200°C immediately after quenching and after pre-aging at room temperature were different from those without Ag. A large shift of the peak temperature of the heat evolution due to the transformation β′–β occurred in the specific heat curves of specimens with Ag pre-aged at room temperature and aged at 100°C after pre-aging. The activation energies of the heat evolutions due to the formation β″ and β′ in the quenched specimens with and without Ag were determined to be 0.92 eV, 1.40 eV, 1.65 eV and 1.70 eV, respectively. From the above considerations, it is concluded that the addition of Ag accelerates the rate of the formation of β″ and stabilizes them.
Pre-aging at room temperature for 75 hr delayed the rate of the formation of β′ from the matrix following by aging at 100°C for 30 min and at 200°C for 45 min.
