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 t he yield strength anisotropy in aluminum alloys was investigated. Stress-ag ing 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 tr eatment conditions. The data was evaluated using the Taylor/ Bishop-Hill mo del for texture-induced anisotropy as well as the plastic and elastic inclu sion 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) 179 7-1262; 30 (1982) 725-737, which incorporate anisotropic particle strengthe ning. In a cube textured Al-Cu alloy containing theta' on only two out of t he three possible {100} variants the maximum deviations in yield strength r eached 14% when compared to conventionally aged material. In an Al-Cu-Mg-Ag alloy containing the Omega phase on {111} and having a strong brass type d eformation texture, less pronounced effects were found after partial remova l of one of the Omega variants. Qualitative predictions of the plastic and elastic inclusion models were in good agreement with the findings for aniso tropic 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 m odel is required. Stress-aging provides a tool to control anisotropy in hig h strength aluminum alloys. (C) 1998 Elsevier Science S.A. All rights reser ved.