Processing maps (with flow instability criterion based on power-law breakdown) integrated into finite element simulations for evaluating the hot workability of 7075 aluminum alloy

Abstract A series of isothermal compression tests were performed on the cast 7075 alloy processed by the electromagnetic stirring method in the temperature range between 573 and 723 K and in the strain rate range of 10-3 and 10 s-1. By analyzing the flow-stress behavior of the alloy as a function of the temperature, strain rate and strain, processing maps were constructed by using the Prasad’s, Murty’s and KJ methods. The processing maps were integrated into the plastic forming process by using the user routines in the finite element simulation software (DEFORM-2D), and the differences between the methods in predicting the power dissipation efficiency and unstable flow conditions during hot compression were compared. For the Prasad’s and Murty’s methods, the calculation of ξ or η is not easy since the definition of ξ in the Prasad’s method includes numerical differentiation and the definition of η in the Murty’s method includes numerical integration. In contrast, for the KJ method, the calculations of η and ξ is easy because they are explicitly expressed as a function of stress exponent, which is beneficial over the other methods in comparison when the input data are coupled with the FEM simulation. Through microstructure observation, the reliability of the FEM simulation coupled with the KJ method was verified.