my ans is:If the material were a single crystal, the yield stress would be lower. The dislocation could move easily because there is only 1 crystal. In addition, single crystal metals have directional stiffness. But I'm not sure about that
Discuss in terms of the possible microstructural differences how the proof
stress of the aluminium alloy tested in bending could be greater than the proof stress of the alloy
tested in the tensile machine. (Be specific to aluminium alloys)