Characterisation of dynamic recovery during hot deformation of spray formed Al–Li alloy (UL40) using processing map approach

Abstract

Processing maps, also known as power dissipation maps, for spray formed Al–Li alloy (UL40), encompassing a wide range of hot working temperature (375–575°C) and strain rate (3 × 10−4–101 s−1) have been developed. The constant true strain rate compression tests were carried out under isothermal conditions to generate the stress–strain data required for computing the efficiency of power dissipation η. The maps exhibit three distinct regimes. The two high efficiency (>55%) regimes occur at the low strain rates (<10−3 s&minus1) and at the high strain rates (>1 s−1), and the other with moderate efficiency values (20–23%) occurs at the intermediate strain rate (10−1 s−1). The latter one has been interpreted to be associated with dynamic recovery (DRV) process while the other two regimes have been found to be associated with cracking processes. The DRV regime in the map has been characterised in terms of stress–strain response, microstructure and tensile ductility. The kinetic rate analysis carried out in the DRV regime suggested that the thermally activated cross-slip is the rate controlling mechanism for the DRV process. The effect of Li addition on the optimum deformation condition of DRV in Al has also been discussed qualitatively.