979-8-3503-4521-6/23/$31.00 ©2023 IEEE Effect of Pulsed Current Frequency on Electroplasticity in Plain Carbon Steel : An Experimental Study Thilini Dhanushka Department of Materials Science and Engineering University of Moratuwa Moratuwa, Sri Lanka mkdtdhanushka@gmail.com Gayan Aravinda Abeygunawardena Department of Materials Science and Engineering University of Moratuwa Moratuwa, Sri Lanka aravindag@uom.lk Indika De. Silva Department of Materials Science and Engineering University of Moratuwa Moratuwa, Sri Lanka indikagip@uom.lk Abstract— This research investigates the impact of the electroplasticity phenomenon on the mechanical behavior of two plain carbon steel samples with different carbon contents (0.09wt.% and 0.39wt.%) under uniaxial tensile loading combined with low-frequency high amplitude electrical pulses. Prior to the tensile tests, all samples underwent normalization heat treatment. The experimental results demonstrate a progressive decrease in yield stress accompanied by an improvement in ductility as the pulse frequency increases, up to a frequency of 0.83 Hz. These findings suggest a positive influence of the electroplasticity effect on the tensile properties of plain carbon steels. However, beyond 0.83 Hz, despite further reduction in yield stress, a gradual decline in ductility is observed until a frequency of 1.64 Hz, primarily attributed to enhanced strain localization and induced defects resulting in premature fracture. Microstructural analysis reveals that the fracture surfaces of samples tested under electrical current exhibit intermediate grain sizes between non-deformed samples and deformed samples tested without current. Additionally, the presence of characteristic dimples on the fractographs further supports the observed variation in ductility with pulse frequency. Notably, the combination of a pulse frequency of 0.83 Hz and an effective current of 777.8 A yields a significant enhancement in formability. Keywords— electroplasticity effect, electrically assisted forming, plain carbon steel, uniaxial tensile test, pulsed current I. INTRODUCTION Steel, especially plain carbon steel, is extensively utilized in engineering applications due to its diverse microstructures and desirable properties achievable through metal forming processes and heat treatments [1,2]. However, traditional metal forming methods have notable drawbacks, leading to the emergence of electrically-assist forming as a solution to enhance metal formability at room temperature while achieving the desired shape and properties [3,4]. The enhancement of plasticity during the tensile deformation of a zinc single crystal by irradiation with a 1 MeV electron beam was first observed by Troitskii and Likhtman [5]. A reduction of ultimate tensile strength and strain hardening exponent with the increase in peak current density was observed for AZ31B magnesium alloy under the uniaxial tensile testing and the tensile testing was performed at 323 ℃. Moreover, for the fracture strain, an optimum pulsed current condition has been observed for improving its elongation [6]. Apart from this, the influence of the electroplasticity effect on tensile properties of magnesium alloys [7,8,20], duplex steel [9] and aluminum alloys [14,15] has been observed by researchers. Flow stress reduction induced by electric current during the plastic deformation of a metal is known as electroplasticity [10]. Several studies have shown that thermal effect caused by joule heating alone is sufficient for the reduction of the flow stress to improve the formability [11,12]. According to those studies, temperature rising due to the joule heating effect will be able to activate the dislocation movement to increase the plasticity of the metal. Several hypotheses, including electron wind force, de-pining of dislocations by paramagnetic obstacles, and grain boundary sliding due to charge imbalance have been suggested as factors affecting electroplasticity in addition to joule heating [8,12- 15]. Although electroplasticity was established in 1960 [16], the factors causing this effect remain unclear, and further analysis of electroplasticity in plain carbon steel is needed. On our previous article [19]; the effect of pulsed current on major mechanical properties (Yield Strength) of low carbon steel was elucidated. Nevertheless, the study was limited to single pulse switching frequency with a steel sample of only single low carbon percentage. In this study, low carbon steel specimens (0.09wt.%) and medium carbon steel specimens (0.39wt.%) were exposed to uniaxial tensile forces at a quasi-static pace. Additionally, AC electrical pulsed current was applied concurrently, utilizing 5 distinct switching frequencies. The objective of this study was to examine the TABLE I. CHEMICAL COMPOSITION OF THE AS-RECEIVED PLAIN CARBON STEEL SAMPLES C (wt.%) Mn (wt.%) Si (wt.%) Cu (wt.%) S (wt.%) Cr (wt.%) Fe (wt.%) 0.09 0.50 0.01 0.005 0.016 0.003 99.2 0.39 0.71 0.23 0.131 0.104 0.087 98.1 TABLE II. EXPERIMENTAL CONDITIONS Carbon content (wt.%) Pulse frequency (Hz) RMS value of current (A) 0.09 0.39 0.55 636.4 777.8 0.66 0.83 1.10 1.64 0 0 6 mm 25 mm 2 mm 20 mm Fig. 1. Detailed design of the specimen