The role of internal stresses on the plastic deformation of the Al-Mg-Si-Cu alloy AA6111

Henry Proudhon (1) , Warren J Poole (1) , Xiang Wang (2) , Yves Jm Brechet (3)

1 Dept. of Materials Engineering
2 Department of Materials Science and Engineering
3 SIMaP - Science et Ingénierie des Matériaux et Procédés

In this work, we have investigated the internal stress contribution to the flow stress for a commercial 6xxx aluminium alloy (AA6111). In contrast to stresses from forest and precipitation hardening, the internal stress cannot be assessed properly with a uniaxial tensile test. Instead, tension-compression tests have been used to measure the Bauschinger stress and produce a comprehensive study which examines its evolution with i) the precipitation structure and ii) a wide range of applied strain. A large set of ageing conditions was investigated to explore the effect of the precipitation state on the development of internal stress within the material. It is shown that the Bauschinger stress generally increases with the applied strain and critically depends on the precipitate average radius and is thus linked to the shearable/non shearable transition. Further work in the case of non-shearable particles shows that higher strain eventually lead to particle fracture and the Bauschinger stress then rapidly decreases. Following the seminal work of Brown et al, a physically based approach including plastic relaxation and particle fracture is developed to predict the evolution of the internal stress as a function of the applied strain. Knowing the precipitation structure main characteristics --such as the average precipitate radius, length and volume fraction-- allows one to estimate accurately the internal stress contribution to the flow stress with this model.

Mots clés: Physical Sciences

Domaines: Matériaux

Henry Proudhon, Warren J Poole, Xiang Wang, Yves Jm Brechet. The role of internal stresses on the plastic deformation of the Al-Mg-Si-Cu alloy AA6111. Philosophical Magazine, 2008, 88 (05), pp.621-640. ⟨10.1080/14786430801894569⟩. ⟨hal-00513861⟩