Aluminium is a lightweight metal that is easy to shape, making it a major asset for lightening vehicles. However, its use in automotive industry is restricted by its low yield strength and tensile strength. High-strength aluminium alloys, such as the 2XXX and 7XXX series, were developed for the aerospace industry, but they present drawbacks for the mass production required in the automotive industry. The high resistance is achieved at the expense of a very limited formability at room temperature, and reaching their full strength requires an expensive heat treatment that can last several days. Alternative processes routes are being developed to make these alloys cost effective for the automotive industry. For example, the use of plastic deformation during warm forming increases the formability and accelerate precipitation [1].

The high resistance of these aluminium alloys is obtained by precipitation hardening. After solution treatment, the alloy is quenched to obtain a saturated solid solution. Usually, the alloy is then artificially aged at a relatively high temperature to improve the diffusion of the alloying elements in the aluminium matrix (thermal energy, vacancy formation…) to form precipitates. Plastic deformation can enhance precipitate formation during ageing by inducing excess vacancies and dislocations [2]. The purpose of this paper is to understand and describe the influence of plastic deformation on precipitation, during artificial ageing, and at room temperature.

Cyclic and monotonic deformation were compared at different strain amplitudes and strain rates. SAXS was used to determine the precipitation state (density, radius, etc.) of deformed samples. In-situ experiments were performed using adapted tensile devices. This method was complemented by DSC to compare the impact of strain on the different steps of precipitation. The precipitates were directly observed by TEM. SEM was also used to determine the dislocation density using the ECCI method [3]. A KWN-type model [4] was developed to specifically account for the effect of deformation on precipitation. Modelled precipitation kinetics were compared with experimental results.

References

[1] L. Couturier, A. Deschamps, F. De Geuser, F. Fazeli, W.J. Poole ; Scripta Materialia, 2017, 136, 120-123.

[2] W. Sun, Y. Zhu, R? Marceau, L. Wang, Q. Zhang,X. Gao, C ; Science, 2019, 363, 972-975.

[3] G.L’Hôte, S.Cazottes, J.Lachambre, M.Montagnat, P.Courtois, J.Weiss, D.Deschanel ; Materiala, 2019, 8, 100501.

[4] M. Perez, M. Dumont D. Acevedo-Reyes; Acta Materialia, 2008, 56, 2119-2132.