Influence of short-term heat treatment on the microstructure and mechanical properties of EN AW-6060 T4 extrusion profiles: Part A

Aluminium alloys are applied in various industrial fields and play an important role concerning weight reduction especially in the automotive industry. Because of their higher strength, age-hardening alloys are commonly preferred. However, the cold formability in comparison to other materials like mild steels is quite low and due to this, complex parts are hardly producible at higher temperatures. One possibility to improve the cold formability of aluminium alloys is the so called tailor heat treatment. In this approach, a short-term heat treatment is conducted to achieve a local softening of the material due to dissolution of strengthening clusters (retrogression). This effect is used to improve the material flow, relief critical forming zones and enhance the overall formability of the material. Afterwards, strength can be increased again by aging. However, up till now tailor heat treatment has mainly been used for aluminium sheet. Further, a holistic process understanding, taking into account all process parameters as well as a complete integration of microstructural findings is missing. Therefore, the dissolution and precipitation behaviour during heating of Tailor Heat Treated Profiles (THTP) from the aluminium alloy EN AW-6060 T4 is investigated. Heating curves from 20 to 600 °C with heating rates of 0.01 up to 5 K/s are recorded, using the differential scanning calorimetry (DSC). Based on the peak temperatures of one DSC-curve, tensile tests were carried out after a comparable heat treatment. It is shown, that the mechanical properties gained by the tensile test correlate with the microstructure results of the DSC measurements. The correlation of the microstructure and the mechanical properties enables the derivation of optimal parameters for the development of THTP through a local softening. In Part B the heat treatment parameter for the subsequent forming process as well as the evolution of the mechanical properties during natural aging after different short-term heat treatments are discussed.