Experimental and numerical investigation of texture evolution and the effects of intragranular backstresses in aluminum alloys subjected to large strain cyclic deformation

Strain hardening in FCC metals and alloys can be accompanied by the formation of deformation induced dislocation microstructures. These microstructures tend to form dislocation cells or nets which are characterized by three-dimensional tangles of dislocations that serve as “cell walls” and less dense internal regions “cell interiors”. The presence of such dislocation microstructure induces intragranular backstresses due to blockage of dislocation passage leading to kinematic hardening at the macroscopic scale. The present work focuses on the effects of dislocation induced backstresses and the accompanying texture evolution on strain hardening behavior of AA 6063-T6 extruded aluminum alloy during cyclic forward-reverse-forward (FRF) simple shear deformation. The accompanying texture evolution is characterized using electron backscatter diffraction (EBSD) texture measurements. The development of the underlying dislocation substructure during the cyclic simple shear loading is determined using transmission electron microscopy (TEM). Furthermore, a new crystal plasticity backstress hardening model is proposed to incorporate the effects of intragranular backstresses due to the dislocation cells substructure. The hardening model is validated by comparing the numerically predicted results against the experimental cyclic simple shear flow response as well as texture evolution. An excellent agreement is found between the simulated and experimental results. In particular, the proposed model is able to predict the experimentally observed Bauschinger effect as well as the accompanying texture evolution during cyclic simple shear testing. The applicability of the proposed backstress hardening model is further validated by applying it to different cyclic strain paths (i.e. tension-compression-tension (TCT) and compression-tension-compression (CTC)) for different strain amplitudes. The numerically predicted results show good agreement to the corresponding experimental cyclic test results.