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The work hardening properties of 99.99% purity aluminum were investigated by tensile tests at RT on samples with average grain sizes between 40 and 300 μm. It is shown that the stress–strain curves can only be described by two different functions valid at moderate and at higher strains, respectively. New constitutive equations due to these two different stages are derived on the basis of a new phenomenological model, and their validity is proved by experimental results. It is shown that the work hardening parameters depend strongly on the grain size in the first stage, while the rate of hardening in the second stage is independent of the grain size. The constitutive equations derived are used to analyze the grain size dependence of the flow stress as a function of the strain.

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