Strain hardening anisotropy of aluminium alloys during complex loading: Strain reversal effects

Two aluminium alloys were prestrained in tension and subjected to a subsequent deformation in simple shear. The shear direction is such that the strain tensor is nearly reversed. In case of the AA1050-O, the stress-strain curves exhibit a behaviour typical of Bauschinger type tests that consists in a transient attenuation of the hardening rate. Transmission electron microscopy observations demonstrate that the transient is related to the dissolution of pre-existing dislocations walls. Due to its high precipitate content, the substructure in the Al-Mg-Si alloy (6022-T4) is composed of a high density of individual dislocations homogeneously distributed. The dislocation arrangement is apparently unaffected during reloading. Consequently, monotonous hardening is recorded at reloading for this alloy.