Effects of preferentially aligned precipitates on plastic anisotropy in Al-Cu-Mg-Ag and Al-Cu alloys

The influence of a preferential alignment of plate shaped precipitates on the yield strength anisotropy in aluminum alloys was investigated. Stress-aging in tension, i.e. externally applied tensile stresses during aging, was utilized to produce preferential nucleation of precipitates on those 100 and 111 habit plane variants that formed the smallest angle with the load. In-plane yield anisotropy was investigated in tension for various heat treatment conditions. The data was evaluated using the Taylor/ Bishop-Hill model for texture-induced anisotropy as well as the plastic and elastic inclusion models proposed by W.F. Hosford, R.H. Zeisloft, Metall. Trans 3 (1972) 113–121 and P. Bate, W.T. Roberts, D.V. Wilson, Acta Metall. 29 (1981) 1797–1262; 30 (1982) 725–737, which incorporate anisotropic particle strengthening. In a cube textured Al-Cu alloy containing θ′ on only two out of the three possible 100 variants the maximum deviations in yield strength reached 14% when compared to conventionally aged material. In an Al-Cu-Mg-Ag alloy containing the Ω phase on 111 and having a strong brass type deformation texture, less pronounced effects were found after partial removal of one of the Ω variants. Qualitative predictions of the plastic and elastic inclusion models were in good agreement with the findings for anisotropic particle strengthening by randomly distributed precipitates. Effects of aligned precipitates coincided somewhat better with predicted trends by the elastic inclusion model, however, additional verification for either model is required. Stress-aging provides a tool to control anisotropy in high strength aluminum alloys.