Experimental Investigation on the Effect of Electrically Assisted Rapid Heating in Bulk Metal Forming

Many industries utilize hot metal forming to reduce forming forces and material flow issues. In this study, electrically assisted (EA) rapid heating is used in direct comparison to conventional heating methods. Three materials were investigated: AISI 4340, Al-7075-T6, and Ti-6Al-4V. Samples were heated at an approximate rate of 100 °C/s before applying compressive loads, simulating forging or other bulk deformation processes. Afterwards, samples were prepared for further microstructure evaluation. It was observed that high-rate temperature increase resulted in some developments in the microstructure and phases, as seen in AISI 4330, for example. Additionally, the effect of electricity was noticed to have a significant impact on flow stresses, as observed in many of the compression tests, immediately following the rapid heating process. Experiments and images from optical microscopy show that samples experienced drastic and immediate decrease in flow stress at all temperatures when using the EA rapid heating method versus the conventional method with seemingly no change to the material microstructure. This may be explained by the lack of phase changes at lower temperatures combined with the effect of electricity. Further investigation into the changes in micro-porosity, intermetallic phases, and changes in precipitates are suggested to supplement the current understanding of the drastic stress drop caused by passing electrical currents through metals.