Identification for the optimal working parameters of Al–Zn–Mg–Cu alloy with the processing maps based on DMM

Abstract

As an important parameter in metal forming process, workability can be evaluated by means of processing maps on the basis of dynamic material model, which are constructed from experimentally generated stress variation with respect to strain, strain rate, and temperature. To obtain the processing map, hot compression tests were performed over a range of temperatures 573∼723 K and strain rates 0.01∼10 s−1. As the true strain is 0.2, 0.4, 0.6, 0.8 respectively, the response of strain rate sensitivity (m value), power dissipation efficiency (η value), and instability parameter (ξ value) to each temperature and strain rate were evaluated. And the processing map for Al–Zn–Mg–Cu alloy was developed by the superimposition of the power dissipation and the instability maps, and the regions having the highest efficiency of power dissipation and negative instability criterion were added for more clarification of low and high workability regions. By the metallographic observations, the grain refinement by dynamic recrystallization under the optimal deformation conditions, and wedge cracks under the unstable deformation conditions were found. The optimal working parameters identified from the processing maps contribute to designing the hot forming process of Al–Zn–Mg–Cu alloy without any defect.