Investigation into the Stress Relaxation Behavior and Microstructural Evolution Under Electropulsing-Assisted Heating in Ti55 Alloy Sheets

Abstract Electrical-assisted stress relaxation (EASR) experiments were conducted on Ti55 alloy sheets under varying electrical parameters. The results show that the stress relaxation rate increases with higher effective current density but with current frequency decreases. To capture this behavior, a stress relaxation model incorporating electrical parameters was developed based on the Arrhenius equation, showing a strong correlation with experimental data. Microstructural evolution during EASR was analyzed using electron backscatter diffraction (EBSD). At an effective current density of 11 A/mm2 and a frequency of 50 Hz, grain rotation and grain boundary sliding were the primary mechanisms. As the current density increased to 12.5 A/mm2, dislocation motion became dominant, contributing to an increased stress relaxation rate and limit, as indicated by local misorientation changes. At a current density of 13.5 A/mm2 and a stable temperature of 834.8 °C, dynamic recrystallization (DRX) emerged as the main mechanism. Analysis of grain locations and subgrain boundaries revealed that DRX occurs through grain boundary protrusion and subgrain movement. Finally, phase transformation was identified as a crucial mechanism at an effective current density of 19.5 A/mm2, inducing temperatures above the phase transition point of Ti55 alloy. This study provides a comprehensive understanding of how electrical parameters influence stress relaxation mechanisms in Ti55 alloy, offering key insights for optimizing high-temperature forming processes in titanium alloys.