SPINODAL DECOMPOSITION IN AI/ZN ALLOYS .3. METALLOGRAPHY AND ELECTRON MICROSCOPY

Decomposition of the quenched spinodal structure in Al/Zn alloys containing from 30 to 60 wt % zinc occurred by discontinuous zinc precipitation in the grain-boundaries followed by precipitation of zinc colonies within the grains. Precipitate morphology differed when solution-treated at 365 as compared to 435° C. Fracture of tensile samples having the spinodal structure was intergranular with but one exception, cold-rolled spinodal structures. Transmission electron microscopy showed significant variation in the size and density of dislocation loops depending upon solution-treatment and ageing conditions. Numerous helical dislocations were also observed. Individual dislocations generally were long and straight. The observed structures are analysed in terms of existing models for vacancy behaviour in alloys. © 1969 Chapman and Hall.