Processing map for hot working of spray formed and hot isostatically pressed Al–Li alloy (UL40)

Abstract

The hot deformation behavior of spray formed + HIPed Al–Li (UL40) alloy was studied using processing map technique. The map has been interpreted in terms of the microstructural processes occurring in situ with deformation, based on the values of a dimensionless parameter η which is an efficiency index of energy dissipation through microstructural processes. An instability criterion has also been applied to demarcate the flow instability regions in the processing map using another parameter ( ξ). Both the parameters ( η and ξ) were computed from the experimental data generated by compression tests conducted at various temperature and strain rate combinations over the hot working range (375–575 °C and 3 × 10 −4 to 1 s −1) of the present material. The processing map exhibits three distinct η domains without any unstable flow conditions under the investigated temperature and strain rate conditions. The dominant microstructural mechanisms corresponding to these domains were identified to be extended dynamic recovery, grain boundary cavitation and flow localization. The stress–strain, microstructure and hot ductility recorded under the deformation conditions of these domains were correlated to the microstructural processes. The ‘safe window’ for hot working of HIPed UL40 material has been identified based on these results. Further, the significance of HIPing on the hot workability has been enunciated by comparing the results of the present material with the as-spray formed material.