EFFECTS OF TEXTURE GRADIENTS ON YIELD LOCI AND FORMING LIMIT DIAGRAMSIN VARIOUS ALUMINUM-LITHIUM SHEET ALLOYS

Marked through-thickness variations of preferred crystallographic orie ntations in aluminum-lithium (Al-Li) sheet alloys have been observed a nd documented. These metallurgical features could have an effect on th e way in which these materials distribute strain during plastic deform ation. From a theoretical or a practical point of view, it is importan t to investigate these texture effects on plastic-deformation properti es and particularly on forming limit strains. In this work, quantitati ve texture data, which were determined by X-ray and neutron diffractio n techniques, were used with a polycrystal model to predict the yield locus of recrystallized and unrecrystallized AA8090 and AA2090 Al-Li s heets. The conventional AA2024 alloy in the annealed condition was als o investigated as a reference material. Subsequently, these yield loci were used to calculate forming limit diagrams (FLDs) in the stretchin g range, using the Marciniak-Kuczynski (M-K) approach with strain rate potentials to describe the constitutive properties of the sheets. A s imple critical thickness-strain criterion was used to predict the FLD in the drawing range. The predicted FLDs were found to be in fair agre ement with experimental curves obtained under punch-stretching conditi ons. In general, experimental trends were accounted for by the results predicted using the average texture data. However, the texture gradie nts do not completely explain the large scatter observed in the experi mental forming limits and the high average limit strain of the recryst allized AA8090.