Polycrystal modeling of precipitate effects on the mechanical behavior of an aluminum-copper alloy

Modeling mechanical behavior based upon a material's microstructural characteristics is a long-standing and complex problem. Precipitation-hardened alloys are regularly used in industrial applications because their mechanical properties can be modified by heat treatments. Aluminum alloys are one example of this group and are becoming increasingly more important in commercial applications that require lightweight, high-strength materials, such as the automotive industry. Precipitation-hardened materials present a complicated modeling problem as different metastable phases can be nucleated in the matrix acting as barriers to dislocation motion. The most versatile model would be capable of describing the changing stress-strain behavior of an alloy resulting from the different hardening mechanisms brought about by the various precipitates.; A physically-based hardening formulation was developed in this work, incorporated into a polycrystal model, and applied to a binary aluminum-copper precipitation-hardened alloy. The alloy was heat treated at 190°C and 260°C for various times and was studied in both polycrystal and single crystal forms. Single crystals eliminated the complicating effects of grain boundaries allowing clear determination of the active deformation mechanisms as well as a detailed study of the effect of precipitates on the flow anisotropy behavior. Pure aluminum was also studied to highlight the change in deformation mechanisms due to the introduction of precipitates in the matrix. Different deformation mechanisms were observed corresponding to the degree of coherency between the precipitate and matrix. The influence of precipitate-induced anisotropy on single crystal flow behavior was clearly established, again relating to the precipitate character.; The physically-based hardening formulation was derived from dislocation theory resulting in both statistical and geometrical storage components, where the distinguishing microstructural length scales were included in the geometrical storage terms. The phenomenon of precipitation-induced anisotropy was incorporated into the hardening description. Model results were compared to single crystal and polycrystal compression experiments. Accurate simulations were obtained for most of the aging conditions and the correct trends due to precipitate-induced anisotropy were predicted.