Effect of heat treatments on discontinuous precipitation kinetics in Al-30 wt.% Zn alloy

The discontinuous precipitation kinetics in Al-30% wt. Zn alloy have been investigated at temperatures ranging from 348 to 503 K (75 to 230 °C) by using an optical microscopy, X-ray diffraction, differential dilatometer, differential scanning calorimetry and microhardness measurement. We have found that at all temperatures less than 180 °C the supersaturated solid solution of quenched alloy was observed to decompose completely by a cellular precipitation reaction. Quantitative metallography methods have been applied to measure the corresponding transformed volume fractions at different temperatures and times of precipitation. The variation of the heating rate and the application of different methods have allowed us to calculate two kinetic parameters of precipitation: the activation energy of the process and the Avrami exponent.