LXXXV. The mechanism of work softening in aluminium

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Abstract
The appearance of slip lines on polished surfaces of aluminium crystals has been studied under the optical microscope as a function of plastic extension at 90°K and at room temperature. Measurements have been made of the lengths of the slip traces produced by the emergence of screw and edge dislocation segments. During deformation at both temperatures the first slip lines produced are long and straight. Further deformation at 90°K results in the appearance of shorter slip traces whilst at room temperature cross slip is observed. Crystals strained at one temperature and subsequently deformed at a higher temperature show a yield point (work softening); this is accompanied by an increase in the amount of cross slip and in the intensity of cross slip traces. The result is discussed in terms of dislocation movements.