Probing precipitation in aluminium alloys during linear cooling via in-situ differential scanning calorimetry and electrical resistivity measurement

Abstract

Investigating precipitation processes in aluminium alloys during cooling from the solutionising temperature is important because the level of solute supersaturation and the presence of pre-precipitated solutes determine the response to the subsequent age hardening step. Differential scanning calorimetry has been developed to a suitable method to follow precipitation over a wide range of cooling rates. We develop a device that allows us to measure electrical resistivity in-situ during the quenching of alloy samples from the solutionising temperature. A procedure is formulated that allows us to separate the signal related to precipitation from the large background caused by the temperature dependence of electrical resistivity. Application to an aluminium alloy 6014 reveals a two-stage precipitation reaction during cooling at rates between 1 and 20 K min^-1, the first related to precipitation of the stable β phase, the second due to the formation of various metastable phases. Comparison between resistivity and DSC signals measured at the same cooling rate shows very close correspondence between the two. Thus, in the future, both methods could be used in a complementary way.