Microstructure and mechanical properties of AA5052 after electromagnetic hydraulic forming

Hydroforming (HF) is a traditional sheet metal forming method with high forming efficiency and reliability. However, under HF, the material at room temperature is easy to crack due to the low strain rate. Electromagnetic hydraulic forming (EMHF) is a high-speed forming process, which can significantly improve the forming limit of materials. Nevertheless, there is a lack of research on the performance and microstructure of parts deformed under EMHF. In this paper, AA5052 sheets are formed into flat bottom parts under the HF and EMHF processes. The tensile properties and hardness of the deformed parts are tested. The yield strength and tensile strength of the EMHF samples were higher by 7.5% and 9.0%, respectively, compared to those of the HF samples. Trans-mission electron microscopy (TEM) and electron backscatter diffraction (EBSD) showed that the EMHF samples had higher internal dislocation density, smaller grain size, higher proportion of small-angle grain boundaries, and higher texture intensity compared to those of the HF samples. This corresponds to the higher strength and hardness observations. Finite element models of the EMHF and HF configurations were developed. The deformation velocity of the EMHF sample exceeded 200 m/s and the strain rate exceeded 600 s-1, while the maximum local liquid pressure reached 211 MPa. The comparison of the thickness distribution obtained by simulation and experimentally indicated that the simulation results were in good agreement with the experimental ones. Moreover, the reasons for the improvement of strength and hardness are discussed, and the strength evolution mechanism is elaborated.