The origin and nature of multiple loop configurations in quenched aluminum and aluminum alloys

Multiple loop configurations in quenched aluminum—silicon alloys are studied using transmission electron microscopy. An analysis of the defect geometries and complex unfaulting behavior is shown to be consistent with the coplanar loop structure. This is in agreement with a recent electron microscopy contrast analysis of multiple loops in an aluminum—magnesium alloy, but contrary to previous studies on nominally pure aluminum where the layered structure is found. A model is developed in which both the layered and coplanar structures can develop depending on the magnitude of the stresses generated around impurity particles. It is also shown how the coplanar loop structure originates from the operation of a Bardeen‐Herring climb source.