Recrystallisation behaviour of twin roll cast commercial aluminium -1% manganese alloy after cold rolling

Abstract

The recrystallisation kinetics of a commercial, twin roll cast 3003 aluminium alloy has been studied by means of restoration of the flow stress during annealing at a constant temperature of 673 K. Particular attention has been paid to the restoration behaviour of the material when it is composed of a ‘hard’ unrecrystallised and a ‘soft’ recrystallised fraction. Evaluation of the hypothesis of equal strain distribution between the fractions present indicates that such a model is not satisfactory. On the contrary, the experimental results imply that such a model predicts a slower kinetics than that observed, particularly regarding restoration of the ‘soft’ fraction. Thus, during deformation of a partially recrystallised material, the consequent applied strain tends to accumulate more in the softer fraction of the aggregate. The restoration behaviour of the alloy investigated indicates that, under some deformation conditions, precipitation of fine secondary particles from the supersaturated matrix can occur concurrently with recrystallisation. Such an interaction gives rise to restoration curves that can be satisfactorily described by means of the integration or convolution of two Johnson - Mehl - Avrami - Kolmogorov (JMAK) equations. It has been determined that the time to achieve a given restored fraction and the recrystallised grain size can be described as functions of the effective strain applied to the material by means of simple parametric relationships. However, the strain dependence of the restoration time has been found to vary significantly with the achieved fraction restored. As the fraction restored increases, the restoration time becomes markedly dependent on the strain applied to the material, which is associated with possible interaction between the recrystallisation and precipitation processes that occur during annealing. Restoration curves determined experimentally for the partially recrystallised alloy can also be satisfactorily described by means of the convolution of two JMAK equations.