Optimum heating time for warm forming of AA7075 aluminum alloy in T6 condition
Résumé
The T6 condition of AA7075 gives the highest elastic strength and ultimate strength of this alloy. To ensure that this condition is obtained at the end of the warm forming process, it is necessary to control the forming temperature (typically 200 ◦C) to avoid any evolution of precipitates and consequent changes in mechanical behaviour. The aim of this work is to determine the optimal warm heating conditions for AA7075 to maintain the T6 state at the end of the forming. To find these parameters, several heating, temperature holding and cooling conditions used duringmulti-stepwarm forming are reproduced on aGleeble machine. Vickers hardness and conductivity measurements, as well as tensile tests, are then carried out to check that this aluminum alloy still complies with the values of the T6 state standard values. A holding time of 10 s, with a fast heating rate of 250 ◦C/s, and a cooling by air quenching prevent the development of precipitates and help to maintain the T6 state. These optimum conditions are finally validated using a multi-step warm forming process of a U-channel part.