The effect of particle content and matrix grain size on the recrystallisation of two-phase aluminium-iron alloys

Abstract

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 Al₃Fe particle spacing decreased from 15 to 4μm. 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 Al₃Fe content increased. These effects have been shown to be independent of the size of the Al₃Fe particles, within the range studied (diameters 0.6 to 2.2μm). 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.