Cyclic hardening and substructure of AlMg alloys

The dislocation substructure and macroscopic regularities of cyclic hardening of aluminium alloy AMg6 are studied in the low and high cycle fatigue regions. The density of dislocations and dislocation loops as well as the microhardnesses of the surface and the near-surface layer are measured as functions of the strain amplitude, the number of cycles, the environment and the temperature. It is found that, as the number of cycles increases, the quantitative evolution of the initial dislocation substructure occurs mainly in the near-surface layer and the cyclic hardening develops in two (the high amplitude region) or three (the low amplitude region) stages. The importance of each structural component is estimated in relation to hardening in these regions. On the basis of our results and reports (on alloys with lower contents of magnesium) in the literature the effects of the stacking fault energy upon the substructures due to cyclic hardening of AlMg alloys are analysed in a wide range of magnesium contents (0-6.5 at.%) together with the difference between the substructures of these alloys and those of pure f.c.c. metals under similar conditions.