Evaluation of different heat treatment cycles on improving single point incremental forming of AA6061 aluminum alloy

Both the formability and hardness of the age-hardenable AA6061 aluminum alloy sheet are highly dependent on the type of the heat treatment. In this research, to simultaneously improve the formability and the final hardness of a truncated pyramid from the AA6061 aluminum alloy formed by single point incremental forming (SPIF), three different heat treatment cycles have been investigated. The considered cycles include solid solution/SPIF/aging (the cycle I), solid solution/aging/SPIF (the cycle II), and annealing/SPIF/solid solution/aging (the cycle III). The maximum forming depth achievable at certain wall angles before fracture was considered as a formability indicator. Microstructural studies were carried out using optical and scanning electron microscopy and differential scanning calorimetry. The obtained results show that the best condition among the investigated heat treatment cycles for SPIF of the 70° wall angle is cold working of the annealed sheet in the cycle III which results in an improvement of 100% in the forming depth and an increase of 2% in the hardness by the subsequent artificial aging treatment, as compared to the as-received condition. Also, microstructural studies revealed that the solution temperature and time considerably affect the formability and hardness of the final formed part during the cycle I.