Analysis of plastic deformation behavior of ultrafine-grained aluminum processed by the newly developed ultrasonic vibration enhanced ECAP: Simulation and experiments

Abstract

In this research, plastic deformation behavior of the commercially aluminum AA-1050 processed by using a newly developed ultrasonic vibration enhanced equal channel angular pressing (UV-ECAP) method has been investigated. A finite element model, including constitutive equations describing the acoustic softening effect, is developed to study the effect of applying high-intensity vibration in the ECAP process. Experiments are carried out to validate model predictions and to characterize microstructure and hardness of processed specimens. The experimental results suggested that the developed FE model is capable of predicting the deformation behavior of aluminum reasonably well under various process parameters. The results showed that applying ultrasonic vibration in frequency 20 kHz and amplitude 15 μm in the UV-ECAP process exhibits 31% reduction in the required load, eliminates the folding defect during ECAP, increases the effective length with reducing the corner gap. The predicted maximum and average equivalent plastic strains of the UV-ECAPed samples exhibited an increase of 33% and 58% comparing conventional ECAP. More uniform Misses stress distribution with lower longitudinal strain inhomogeneity factor were achieved in this process. The microhardness exhibited an increase by a factor of about 2.1 after first pass of UV-ECAP on aluminum. The average grain size of specimens was measured about 2.6 μm and 1.7 μm after one and two passes of UV-ECAP process respectively. It is found that a greater ultrasonic energy is required to maintain the efficiency of the UV-ECAP method in higher passes due to enhanced work-hardening caused by ultrasonic vibration in the specimen.