Kinetics of Solid-State Reactions in Al-Li-Cu-Mg-Zr Alloys from Calorimetric Studies

Abstract

Differential scanning calorimetric (DSC) studies at different heating rates have been carried out to examine the solid-state reactions in 1441 and 8090 Al-Li-Cu-Mg-Zr alloys of water-quenched (WQ) and retrogressed tempers. The DSC peaks indicating the reactions sequence such as formation of GPB zones, precipitations of d¢ phase, dissolution of GPB zones and d¢ precipitates, and precipitations of S¢, T 1 , T 2 , and d phases have been identified. From the heat flow associated with the peaks of the thermograms, the fraction transformation (Y), the rate of transformation (dY/dt), the activation energy (Q*), the frequency factor (k 0 ), and the transformation function f(Y) for all the reactions of the 1441 and 8090 alloys have been determined. The appearance of separate peaks of GPB zone formation and d¢ precipitation in the 1441 alloy of retrogressed tempers has enabled determination of the kinetic parameters, which is otherwise not possible from the thermograms of the WQ state due to peak overlapping, by varying heating rate method. The kinetic parameters determined from the DSC data of all the reactions of the alloys are in good agreement with the previously published data.

Precipitation during Quenching in 2A97 Aluminum Alloy and the Influences from Grain Structure

“…There are three endothermic peaks (A, D and F) and three exotherm peaks (B, C and E) existing in the DSC thermogram of the WQ specimen. Endothermic peak A, observed in the temperature range of 90–120 °C, marked the dissolution of Li clusters and GP zones, referring to the previous research [ 27 , 28 , 29 ]. The exotherm peak B at approximately 138 °C indicates the precipitation of GP zones [ 27 , 28 , 30 , 31 , 32 ].…”

“…Endothermic peak A, observed in the temperature range of 90–120 °C, marked the dissolution of Li clusters and GP zones, referring to the previous research [ 27 , 28 , 29 ]. The exotherm peak B at approximately 138 °C indicates the precipitation of GP zones [ 27 , 28 , 30 , 31 , 32 ]. The precipitation of δ′ phase contributes to the peak C at about 180 °C [ 27 , 28 , 30 , 31 , 32 ].…”

“…The exotherm peak B at approximately 138 °C indicates the precipitation of GP zones [ 27 , 28 , 30 , 31 , 32 ]. The precipitation of δ′ phase contributes to the peak C at about 180 °C [ 27 , 28 , 30 , 31 , 32 ]. The appearance of the endothermic peak D between 190 °C and 230 °C proves the dissolution of GP zones and δ′ phase that formed in the temperature range of peak B and peak C [ 27 , 28 , 30 , 31 , 32 ].…”

“…The precipitation of δ phase contributes to the peak C at about 180 • C [27,28,[30][31][32]. The appearance of the endothermic peak D between 190 • C and 230 • C proves the dissolution of GP zones and δ phase that formed in the temperature range of peak B and peak C [27,28,[30][31][32]. The intense exotherm peak, marked by peak E, is observed in the temperature range of 250-320 • C. Despite the coexistence of T 1 , δ, S and T2 phase reported by the literature [28,30,31,33], the precipitation of the T 1 phase is believed to contribute dominantly to the exotherm [34][35][36].…”

Dissolution and Precipitation Behaviour during Continuous Heating of Al–Mg–Si Alloys in a Wide Range of Heating Rates

“…It is generally accepted that an increasing heating rate shifts the reactions towards higher temperatures (e.g., [ 10 ]). This phenomenon is often used to evaluate kinetic parameters such as the activation energy for specific precipitation reactions (e.g., [ 11 , 12 , 13 ]). A number of different methods exist to evaluate such kinetic parameters [ 14 , 15 ].…”