An experimental assessment of grain size effects in the uniaxial straining of thin Al sheet with a few grains across the thickness

The mechanical behaviour under uniaxial tension of polycrystalline 99.999 at.% Al sheet with a thickness of a single or a few crystallites is investigated experimentally. The specimens are cold rolled to a thickness (t) of 100 up to 340 μm and the grain size (d) is varied by recrystallisation between 75 and 480 μm. All specimens have a similar texture and a regular grain structure. For t/d < 1 the flow stress varies only slightly with t/d, independently of t or d itself. For 1 < t/d < 3, a strong increase in the flow stress is observed. The main explanation for this different behaviour in tension, stems from the grain boundaries parallel to the specimen surface, impacting the deformation and rotation of the grains. Furthermore, it is shown that a single Hall–Petch type relation does not apply to these kinds of specimen. Extrapolations towards specimens with columnar grains are made through the analysis.