Recent publications [1,2] describe a mechanical training procedure for high strength aluminum alloys which is based on cyclic plasticity. A tailored load profile is applied in which an alternating tension-compression stress state is always kept close to the yield strength of the material, which is increasing with time due to the formation and growth of precipitates. Vacancies which are continuously introduced by plastic deformation enable diffusion within the aluminum matrix and thus promote formation and growth of precipitates. The mechanical training can therefore replace a traditional heat treatment used for precipitation hardening. In the ongoing project “ResAlFat” of the Sustainability Center Freiburg (LZN) [3], this idea is investigated as a basis to develop more energy efficient processing routes for aluminum used in engineering applications. The training as initially published by the group of Hutchinson [1] is investigated to adjust the mechanical properties of 2024, 6061 and 7075 aluminum alloys with respect to static strength and fatigue properties. The results of [1,2] (initially based on conventional tensile and fatigue specimens) are reproduced with micro specimens (typical cross section of the measurement region of approx. 200 x 200 µm²) which enable in situ observation of the damage mechanisms during tensile and fatigue tests. Using larger bending specimens, the plasticity induced hardening mechanism is investigated also for component-like stress gradients. The energy consumption of a traditional heat treatment is compared to the mechanical training for an exemplary scenario highlighting its potential for a greener aluminum processing.

[1] Sun et al. Precipitation strengthening of aluminum alloys by room-temp. cyclic plasticity. Science 2019(363):972–5
[2] Zhang et al. Training high-strength aluminum alloys to withstand fatigue. Nature Communications 2020(11:5198).
[3] Project “ResAlFat”, Sustainability Center Freiburg (LZN), 2022-2024, https://www.leistungszentrum-nachhaltigkeit.de/projekte-des-lzn/pilotprojekte/resalfat/