In-situ deformation of aluminium alloy polycrystals observed by high-voltage electron microscopy

In-situ deformation of aluminium alloy polycrystals has been investigated within a high-voltage transmission electron microscope in order to observe dislocation phenomena related to the PortevinLe Chatelier effect. The alloys examined are commercially pure aluminium, binary Al2 at.% Ag, Al2 at.% Zn, Al2 at.% Mg and a commercial alloy containing approximately 5 at.% Mg. All the materials tested exhibit flow-stress discontinuities during room temperature deformation, although the amplitude of serrations is substantially higher in the material containing Mg. In-situ deformation is correspondingly discontinuous in all cases but the co-ordination of dislocation motion in the material containing Mg is markedly higher. Deformation in all the material examined is characterised by the sudden activation and collective motion of multiple dislocations, but this is predominantly confined to a single-slip system in the case of alloys containing Mg. In contrast, alloys which do not contain Mg exhibit concurrent, dispersed slip on multiple intersecting slip systems characterised by extensive cross-slip.