The Effect of Particle Content and Matrix Grain Size on the Recrystallisation of Two-Phase Aluminium-Iron Alloys

The recrystallisation of aluminium alloys in the composition range 0.002 to 1.08 wt % iron has been followed metallographically and by hardness measurements. The recrystallisation of solid-solution alloys was retarded as the iron content increased, whereas that of the two-phase alloys was accelerated. This latter effect was associated with a marked increase in nucleation rate, with no significant change of growth rate, as the Al(3)Fe particle spacing decreased from 15 to 4 mu m. Decreasing the grain size of the two-phase alloys, at constant composition, also caused an acceleration of recrystallisation, the magnitude of which decreased as the Al(3)Fe content increased. These effects have been shown to be independent of the size of the Al(3)Fe particles, within the range studied (diameters 0.6 to 2.2 mu m). The results are discussed in terms of a model (which is based on metallographic observations) of nucleation at matrix grain boundaries and at particle/matrix interfaces. It is suggested that the retardation of nucleation, observed by other workers, in more closely spaced dispersions, occurs because nucleation at particle/matrix interfaces becomes difficult when the inter-particle spacing becomes of the same order as the diameter of the sub-structure of the deformed matrix.