Effect of natural ageing and pre-straining on strength and anisotropy in aluminium alloy AA 6016

During processing of age-hardenable AA 6xxx series alloys for automotive applications the sheets may experience significant time spans between solution heat treatment at the aluminium supplier and age hardening upon the final paint bake cycle at the carmaker. Natural ageing during these pause times and intermediate deformations by sheet levelling or forming operations both affect materials properties of autobody sheet. In the present study we explore the impact of a combination of natural ageing and pre-straining on the tensile properties and the in-plane anisotropy of alloy AA 6016. Materials properties are modelled with the help of a nano-scale material model called NaMo, which consists of a precipitation model simulating the formation of clusters and phases upon natural ageing as input to a mechanical model simulating the evolution of yield strength and work hardening as a function of natural ageing and pre-straining. Plastic anisotropy is modelled by polycrystal-plasticity simulations under consideration of latent hardening to account for strain path change effects introduced by the pre-straining.