Low cycle fatigue at room temperature of over ageing cast aluminium alloys

After a cumulative plastic strain of 2%, a secondary hardening appears. TEM observations show that a homogeneous distribution of dislocations takes place before the secondary hardening and that a heterogeneous distribution of dislocations develops during tho secondary hardening. These heterogeneous substructures correspond to hard dislocation bundles or cells of high dislocation density surrounded by soft regions of low dislocation density. This anisotropic dislocation distribution promotes substantial long range interactions and gives rise to internal stress X. Using the composite model of Mughrabi, the intercellular stress can be calculated.