Met. Mater. Int., Vol. 16, No. 4 (2010), pp. 523~531 doi: 10.1007/s12540-010-0802-4 Published 26 August 2010 Calorimetric Study of Precipitation Kinetics of Al–Cu–Mg and Al–Cu–Mg–0.06 wt.% Sn Alloys Sanjib Banerjee 1, * , P. S. Robi 1 , and A. Srinivasan 2 1 Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India 2 Department of Physics, Indian Institute of Technology Guwahati, Guwahati 781039, India (received date: 31 October 2009 / accepted date: 10 April 2010) Al–Cu–Mg alloy and Al–Cu–Mg alloy micro alloyed with 0.06 wt.% of Sn were prepared by casting route. Precipitation kinetics of these alloys was studied by differential scanning calorimeter (DSC) from 50 ° C to 550 ° C at constant heating rates of 10 ° C/min, 15 ° C/min, 20 ° C/min and 25 ° C/min. DSC curves of the Al– Cu–Mg alloy revealed two exothermic peaks in the temperature ranges from 245.3 ° C to 257.5 ° C and from 267.7 ° C to 288.3 ° C. For Al–Cu–Mg–0.06 wt.% Sn alloy, two similar exothermic peaks were observed in the temperature ranges from 233.5 ° C to 252.1 ° C and from 271.3 ° C to 296.7 ° C. Both peak temperatures increased with increase in heating rate. The reaction kinetics was investigated and the kinetic parameters of the rate equation were determined from the experimental results by using a new methodology. Activation energy of precipitation increased from 96.3 kJ/mole to 99.1 kJ/mole for the first exothermic peak and decreased from 78.0 kJ/mole to 69.0 kJ/mole for the second exothermic peak due to trace addition of 0.06 wt.% of Sn. Fairly good accuracy was obtained when the rate of reaction predicted using the derived parameters was compared with the experimental values. Keywords: alloys, casting, precipitation, thermal analysis, differential scanning calorimeter (DSC) 1. INTRODUCTION Aluminum alloys, especially the precipitation strength- ened 2XXX, 6XXX and 7XXX series of alloys, have been developed for aircraft and space applications, mainly due to their high strength to weight ratio. The present research trend is to microalloy these materials with elements like Sn, In, Cd, Ag, etc. [1-7] in order to achieve higher strength com- bined with reasonable toughness and low density. The pre- cipitation strengthening in these alloys is accomplished by a sequence of solutionising heat treatment at elevated temper- ature, quenching to room temperature, and precipitation heat treatment at some intermediate temperature for a sufficient period of time. During this precipitation heat treatment, brit- tle second phase particles precipitate uniformly in the alumi- num matrix, thereby increasing the strength. In Al–Cu alloys, the equilibrium precipitate phase is CuAl 2 ( θ). The sequence of formation of the precipitates in the matrix can be repre- sented as: GP-zones (clusters, which are generally mono-atomic lay- ers of Cu on (001) planes of Al lattice) →θ" (thin discs, fully coherent with the matrix) →θ' (disc shaped and semi-coher- ent with the matrix →θ (CuAl 2 , which is spherical and inco- herent at the precipitate-matrix interface). The strength and ductility achieved by the alloy depend on the composition, aging time and precipitation temperature. For a particular alloy composition, the activation energy (Q), which denotes the energy required for formation per mole of precipitates, is assumed to be constant for a reaction, and the kinetics of precipitation is governed by the precipitation tem- perature and time. Differential scanning calorimetry (DSC) is generally used to determine the kinetic parameters of the precipitation hardening process. A method was adopted to get the value of Q and the fre- quency factor (k0 ) by fitting the experimental plot of the mole fraction transformed (Y) vs. temperature (T) with the theoretical one, while studying the precipitation and dissolu- tion kinetics in aluminum alloys 2219 and 7075 [8]. In some other methods, the rate constants were evaluated by consid- ering first order reaction kinetics; Q value was calculated for aluminum alloy 2219 [9]. Kissinger was able to evaluate Q and k 0 values from differential thermal analysis (DTA) experi- ments by studying homogenous reactions following the first *Corresponding author: sanjibb@iitg.ernet.in ©KIM and Springer