Abstract
We use a systematic approach to investigate the influence of the specific solution condition on quench-induced precipitation of coarse secondary phase particles during subsequent cooling for a wide range of cooling rates. Commercially produced plate material of aluminum alloy EN AW-6082 was investigated and the applied solution treatment conditions were chosen based on heating differential scanning calorimetry experiments of the initial T651 condition. The kinetics of the quench-induced precipitation were investigated by in situ cooling differential scanning calorimetry for a wide range of cooling rates. The nature of those quench-induced precipitates was analyzed by electron microscopy. The experimental data was evaluated with respect to the detrimental effect of incomplete dissolution on the age-hardening potential. We show that if the chosen solution temperature and soaking duration are too low or short, the solution treatment results in an incomplete dissolution of secondary phase particles. This involves precipitation during subsequent cooling to start concurrently with the onset of cooling, which increases the quench sensitivity. However, if the solution conditions allow the formation of a complete solid solution, precipitation will start after a certain degree of undercooling, thus keeping the upper critical cooling rate at the usual alloy-specific level.
Highlights
The most important heat treatment which allows to increase the strength of several aluminum alloys is the age-hardening heat treatment [1]
The solution-annealing temperature was chosen as 540 ◦ C in several previous investigations of the quench sensitivity of AlMgSi alloys [4,5,12]
As derived from findings in Schumacher et al [20], it can be expected that the specific solvus temperature will be reduced by up to a few tens of Kelvin at even lower heating rates or under isothermal solution-annealing conditions
Summary
The most important heat treatment which allows to increase the strength of several aluminum alloys is the age-hardening heat treatment [1]. Within this heat treatment, solution annealing, which is the generation of a solid solution, establishes the basis for the potential decomposition of solid solutions by quench-induced precipitation and/or supersaturation of the solid solution during subsequent cooling. Quench-induced precipitation reduces the age-hardening potential by lowering the amount of solutes after cooling (prior to aging). This phenomenon is commonly called quench sensitivity. The upper critical cooling rates (uCCR) required to completely suppress quench-induced precipitation, depend on several aspects, for instance, alloy composition
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