Hot deformation behaviour of particle-stabilized structures in Zr-bearing Al alloys

The hot-deformation behaviour of a cold-rolled Zr-bearing Al-Mn alloy and a commercial superplastic Al-Cu-Zr alloy has been investigated. During hot-deformation the subgrain size increased while the density of Al₃Zr particles decreased with increasing strain. The decrease in particle density was caused by a discontinuous dissolution reaction at migrating sub-boundaries. This dissolution resulted in a subsequent reprecipitation of Al₃Zr particles (the metastable phase). The strain-induced subgrain growth process has been classified as a continuous recrystallization reaction. In the superplastic alloy, grain growth ceased above a certain deformation level. The subgrain growth is interpreted as being a result of the strain-induced decrease in particle density. The kinetics has been discussed in terms of a two-stage model where the initial stage is associated with the discontinuous dissolution of the Al₃Zr particles. During the later stage the effects of undissolved and reprecipitated particles have been considered. The stabilization of the grain size during deformation of the commercial superplastic alloy is an effect caused by the presence of a coarse distribution of Cu-rich particles.