Systematic comparison between electromagnetic repulsive and attractive forming for aluminum alloy tube expansion

Electromagnetic attractive forming (EMAF) has shown significant value in expanding the range of electromagnetic forming (EMF) process applications, but it faces difficulties in realization, and current research is still mostly limited to the preliminary method validation stage. To address this issue, an easy to implement and efficient EMAF approach is developed, which successfully realizes the effective expansion of 6061-O aluminum alloy tubes through the introduction of an inner die and the optimization of the coil current waveform and frequency. On this basis, the comparison between EMAF process and conventional electromagnetic repulsive force forming (EMRF) in terms of macroscopic morphology, deformation behavior and microstructure is performed. The experimental and simulation results show that, although EMRF samples can obtain a fuller contour shape, there are problems such as significant wall thinning and serious orange peel phenomenon on the surface. In contrast, EMAF samples not only have more uniform wall thickness distribution, but also show better surface forming quality. This difference is mainly due to the different mechanisms of the axial Lorentz force, which inhibits the material flow during the EMRF process, while promotes the material flow during the EMAF process. Further, microstructural analysis shows that the EMRF process induces significant grain refinement, while EMAF has less effect on grain size. This may be attributed to the significant difference in strain rate between the two forming processes. This study not only expands the application prospects of EMF technology, but also provides an important experimental basis for understanding different EMF forming mechanisms.