Latent hardening and plastic anisotropy evolution in AA6060 aluminium alloy

Abstract

The crystal plasticity theory predicts that hardening on a particular slip system and its corresponding work-hardening rate will depend on the slip activity on both this slip system and all others. The exact form of this dependence is defined by the latent hardening description in form of the latent hardening matrix or the interaction matrix. It has been assumed that this matrix describes the relative strength of various dislocation interactions and is therefore the same for a wide range of alloys with the same lattice structure. Different methods have been used to estimate the values of the interaction matrix components: one is experimental and uses strain-path changes; another simulates the dislocations dynamics in a crystal directly at the microscale and estimates the strength of the forming locks. In this work, the influence of the interaction matrix (and thus latent hardening) on the development of plastic anisotropy is studied. An extruded AA6060 alloy is tested in uniaxial tension in different directions and the anisotropy of the alloy is found to evolve considerably throughout the deformation. A crystal plasticity model is used to simulate the experimental tests, and the use of different interaction matrices is evaluated. A noticeable influence on the predicted evolution of plastic anisotropy as well as the stress-strain field and slip inside the constituent grains is found.

A microstructure-based yield stress and work-hardening model for textured 6xxx aluminium alloys

“…The information about the solid solution concentration and the precipitate particles comes directly from the precipitation model of NaMo. The results from two series of tensile tests have been reported previously by Khadyko et al for different temper conditions of the AA6060 and AA6082 alloys with pronounced texture [40] and for different material directions of the AA6060 alloy [41]. In the current paper, these experimental results were compared to the predictions of NaMo with and without the crystal plasticity modification.…”

“…The predictions of the strain ratio could be improved by using a more advanced homogenisation method, namely modelling individual grains with one or several finite elements (CP-FEM). The results in [41] indicate that CP-FEM allows to obtain more quantitatively accurate prediction of the anisotropy in plastic flow. Concerning the flow stress ratio, the experimental results seem to show that the texture is not the only source of strength anisotropy for the AA6060 alloy.…”

“…The two series of quasi-static tensile tests on cylindrical specimens of aluminium alloys AA6060 and AA6082, previously reported by Khadyko et al [40,41], are briefly recapitulated in the following for completeness. The compositions of the two alloys are given in Table 1.…”

“…This parameter was found for the 90° direction by fitting the corrected stress-strain curve found from Equation (1) to the equivalent stress-strain curve found from the optimization procedure described above. The obtained value of 0.9 k = was then used for all other orientations, while p u θ ε was found directly from the directional tensile tests, see [41] for a more detailed account of the procedure.…”

Reviewing the class of Al-rich Ti-Al alloys: modeling high temperature plastic anisotropy and asymmetry

“…Activation of a slip system depends not only on the orientation but also on the deformation history, which contributes to the hardening (Khadyko et al 2016). This function is responsible for deformation history effects and it depends on the plastic flow accumulation ν α with two related material parameters φ 0 and δ as given in Eq.…”