An electron microscope study of dislocation arrangements in fatigued Al + 1% Mg crystals

Abstract

A study has been made by transmission electron microscopy of aluminium + 1% magnesium crystals fatigued in plane bending. A specimen preparation technique has been used that allows selected areas of a fatigued surface to be examined. It is shown that a surface sub-structure exists, which is associated with ‘persistent markings’ observed optically. Electron micrographs of areas between striations show bands of loops and line dislocations similar to those observed in copper and other face-centred cubic metals, but quite different from the structures seen in fatigued aluminium crystals. It is suggested that the sub-structure is formed as the result of a stress concentration effect at the roots of intrusions, and that the differences between fatigue structures observed in aluminium and aluminium-magnesium crystals are explainable in terms of ease of cross-slip.