Behaviour of extruded aluminium alloys under proportional and non-proportional strain paths

The behaviour of the extruded aluminium alloys AA7003-T6 and AA6063-T6 under proportional and non-proportional strain paths is studied. Uniaxial tension tests in different directions are carried out for as-received profiles and profiles pre-strained in uniaxial tension. Both alloys are seen to be strongly anisotropic with respect to strength, plastic flow and elongation. The characteristic anisotropy differs between the two alloys owing to the different grain structures and textures. Two linear transformation-based anisotropic yield functions are evaluated for the alloys. It is found that the Yld2004-18p yield function proposed by Barlat et al. [Barlat, F., Aretz, H., Yoon, J.W., Karabin, M.E., Brem, J.C., Dick, R.E., 2005. Linear transformation based anisotropic yield functions. Int. J. Plasticity 21, 1009–1039] accurately represents the experimental data for both alloys. With some exceptions, pre-straining leads to an increase of the flow stress and a transient increase in the work-hardening rate. After the transient phase, the work-hardening rates are about the same for the as-received and pre-strained material. The increase of the flow stress is directional, and most significant for orthogonal sequences.