An improved modelling framework for strength and work hardening of precipitate strengthened Al-Mg-Si alloys

A modelling framework for the strength and work hardening contributions in age hardened Al-Mg-Si alloys is presented. The modelling work is based on transmission electron microscopy (TEM) measurements of the needle shaped precipitate lengths and cross sections, and on stress-strain curves up to fracture, obtained by tensile tests applying a necking correction. For strains beyond the uniform limit, further work hardening is found to be strongly suppressed by the presence of the precipitates. At strains up to about 10-15%, new models are proposed for the description of the work hardening at different aging conditions. A detailed way of accounting for the contribution from generation of dislocation loops around non-sheared precipitates is formulated, based on the precipitate size and shape distribution. However, this mechanism overestimates the work hardening, and as an alternative, a new mechanism is suggested, assuming that the precipitates act as obstacles for moving dislocations and contribute to restrict their average slip length, leading to increased storage rate of the dislocations. The model captures measured stress-strain curves at different aging conditions well.

Automated summary

A modelling framework is presented for understanding the strength and work hardening contributions in age hardened Al-Mg-Si alloys. The model is based on TEM measurements of precipitate lengths and cross sections, as well as stress-strain curves obtained from tensile tests. The presence of precipitates strongly suppresses further work hardening beyond the uniform limit. New models are proposed to describe the work hardening at different aging conditions. The contribution from dislocation loops around non-sheared precipitates is taken into account, but an alternative mechanism suggesting that the precipitates act as obstacles for dislocation motion is also suggested.