Abstract
In the present study, the dissolution and precipitation behaviour of four different aluminium alloys (EN AW-6005A, EN AW-6082, EN AW-6016, and EN AW-6181) in four different initial heat treatment conditions (T4, T6, overaged, and soft annealed) was investigated during heating in a wide dynamic range. Differential scanning calorimetry (DSC) was used to record heating curves between 20 and 600 °C. Heating rates were studied from 0.01 K/s to 5 K/s. We paid particular attention to control baseline stability, generating flat baselines and allowing accurate quantitative evaluation of the resulting DSC curves. As the heating rate increases, the individual dissolution and precipitation reactions shift to higher temperatures. The reactions during heating are significantly superimposed and partially run simultaneously. In addition, precipitation and dissolution reactions are increasingly suppressed as the heating rate increases, whereby exothermic precipitation reactions are suppressed earlier than endothermic dissolution reactions. Integrating the heating curves allowed the enthalpy levels of the different initial microstructural conditions to be quantified. Referring to time–temperature–austenitisation diagrams for steels, continuous heating dissolution diagrams for aluminium alloys were constructed to summarise the results in graphical form. These diagrams may support process optimisation in heat treatment shops.
Highlights
Al–Mg–Si alloys can be strengthened through precipitation hardening
Energy has to be supplied if chemical bonds dissociate, which refers to an endothermic reaction
Aluminium alloy dissolutions correspond to endothermic reactions while precipitations belong to exothermic reactions
Summary
Al–Mg–Si alloys can be strengthened through precipitation hardening. The process consists of solution annealing, quenching, and ageing; it contains heating, cooling, and isothermal steps, and thereby precipitation and dissolution reactions occur. The knowledge of the precipitation and dissolution behaviour of aluminium alloys is important for optimising heat treatment steps and acquiring information for simulation in the production chain. Knowledge of the dissolution behaviour over a wide dynamic range would help to select an appropriate heating rate, generate a full solution already during heating, and exhaust the full age-hardening potential. Another important field of application of dissolution is heat treatments which lead to an increase of plastic formability. This holds for forming processes such as tailored heat treated blanks (e.g., [1]), and for joining processes such as laser-assisted clinching [2]
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