Theory of high-strain-rate superplastic flow in particulate-reinforced aluminium composites

Through analysing the effects of grain size and temperature on the strain rate of superplastic aluminium composites and several other kinds of superplastic aluminium material, it is clear that microstructure is related to the superplastic test temperature. The more thermally stable microstructure, the higher test temperature. The strain rates increase with decreasing grain size and with increasing rest temperature. Grain-boundary sliding (GBS) and interfacial sliding (IS) with accommodation of dislocation movements along grain boundaries are considered to be the deformation mechanisms of superplastic composites at temperatures slightly below the solidus temperature. On the other hand, their deformation mechanisms are considered to be GBS and IS with accommodation of dislocation movements and of liquid phase at temperatures slightly higher than the solidus temperature. A deformation model for superplastic particle-reinforced composites is set up. Accordingly, superplastic constitutive equations are developed for temperatures just below and above the solidus temperature of the composite. The theoretical predictions derived from the proposed constitutive equations are in a reasonable agreement with published experimental results of normal flow stress and normal strain rate obtained at test temperatures below and above the solidus temperature.