Modelling of the Pre-Strain Dependent Age Hardening Response in AA6000 Series Aluminium Alloys

The usual application of AA6000 series aluminium alloys in the automotive industry consists of forming the material in a soft T4 temper and applying a post-forming heat treatment, artificially ageing the material to achieve a higher final component strength. The strengthening response of a given AA6000 alloy has been found to depend on the heat treatment parameters as well as the amount of plastic deformation the material has undergone during the forming process. As a consequence, an inhomogeneous distribution of mechanical properties occurs over the finished component. In this work, a method of modelling the pre-strain dependant age hardening response of the material to be used in finite element simulations on the component level is presented. A microstructural model of the precipitation process has been applied to predict the material properties after age hardening as a function of the thermal exposure as well as the accumulated plastic deformation in the material. The results of the microstructural model are then implemented into a finite element analysis to determine the behaviour of components produced in this manner under high levels of plastic deformation (e.g. automotive crash simulation). Initial validation of the method is carried out on the example of a uniaxial tensile test; final validation is conducted using top-hat type tubes under axial crushing.