J. FENG et al.: EFFECT OF OUTPUT VOLTAGE ON AN AZ91D MAGNESIUM ALLOY ROLLED USING ... 113–120 EFFECT OF OUTPUT VOLTAGE ON AN AZ91D MAGNESIUM ALLOY ROLLED USING AN ELECTRIC PULSE TREATMENT VPLIV VHODNE NAPETOSTI NA MAGNEZIJEVO ZLITINO VRSTE AZ91D, VALJANE POD VPLIVOM ELEKTRI^NIH IMPULZOV Jing Feng 1 , Yuezhang Zhou 2 , Dehua Liu 1 , Yong Zhang 3 , Guihong Geng 1* 1 School of Materials Science and Engineering, North Minzu University, Yinchuan 750021, P.R. China 2 Beijing Chemical Industry Research Institute Co., Ltd, Beijing 100080, China 3 State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, Beijing 100083, China Prejem rokopisa – received: 2023-07-27; sprejem za objavo – accepted for publication: 2024-01-11 doi:10.17222/mit.2023.960 Magnesium alloys have poor deformation properties at room temperature, and the application of an electric pulse current during deformation can improve the plastic-forming ability. In this study, the electric pulse rolling of AZ91D magnesium alloy speci- mens has been examined by changing the pulse output voltage. The results demonstrate that the best surface quality and lowest content (8.4 %) of the -Mg17Al12 phase are achieved at an output voltage of 300 V. EBSD tests have revealed the lowest weave strength on {0002} and {1010} at a pulse output voltage of 300 V, as well as the greatest enhancement of twinning. The maxi- mum tensile strength was 165 MPa at an output voltage of 300 V, with a maximum elongation of 4.1 % at an output voltage of 200 V. Keywords: output voltage; electric pulse rolling; AZ91D magnesium alloy; properties Zlitine na osnovi magnezija se slabo deformirajo pri sobni temperaturi, vendar uporaba elektri~nih tokovnih impulzov med deformacijo lahko izbolj{a njihovo sposobnost za plasti~no preoblikovanje. V tem ~lanku avtorji opisujejo {tudijo valjanja magnezijeve zlitine vrste AZ91D spodbujeno z elektri~nimi impulzi razli~no visoke vhodne) napajalne napetosti. Rezultati preizkusov so pokazali, da so avtorji dosegli najbolj{o kvaliteto povr{ine in najmanj{o vsebnost (8,4%) intermetalne faze -Mg17Al12 pri napetosti 300V. Preiskave s pomo~jo spektrostopije s povratno sipanimi elektroni (EBSD; angl.: electron back scattered dispersion) so pokazale najmanj{o zvojno trdnost na kristalografskih ravninah {0002} in {1010} pri 300V tokovnih impulzih ter najve~je pove~anje dvoj~enja. Najve~ja natezna trdnost izbrane zlitin 165 MPa pri napetosti 300 V in maksimalni raztezek zlitine 4,1% so dosegli pri napetosti 200 V. Klju~ne besede: zunanja (napajalna) napetost, valjanje pod vplivom elektri~nih impulzov, magnezijeva zlitina vrste AZ91D, lastnosti 1 INTRODUCTION Magnesium alloys exhibit a high specific strength and stiffness, good electrical and thermal conductivity and electromagnetic shielding properties with excellent casting properties. The use of these alloys as structural parts in automotive, aerospace, electronic products and communication equipment represents wide-ranging ap- plications. 1–3 However, the room-temperature deforma- tion of these alloys is poor, preventing cold rolling, cold stamping and other cold-deformation methods for mass production. Moreover, under hot-forming conditions the magnesium alloy readily undergoes oxidation with asso- ciated mold surface friction and wear. There is now an urgent need to develop a new and efficient plastic-form- ing process for magnesium alloys that can be used in in- dustrial production. In recent years, researchers have found that the appli- cation of a pulse current during the deformation of metal materials can effectively improve the plastic-forming ca- pability, and this phenomenon is termed the "electro- plastic effect". 4,5 The use of pulsed currents has now been applied in various plastic-forming processes. 6–9 The pulsed current can reduce flow stress in metallic materi- als by influencing the movement and proliferation of dis- locations. 10–12 Zhou Yizhou et al. 13,14 found that brass and steel produced by cold rolling formed ultrafine grains in a short time after the electric pulse treatment, which sub- stantially improved the overall mechanical properties of the material. In the pulsed current treatment of cold-rolled Cu-Zn alloys, Dai Wenbin et al. 15,16 observed a current induced recrystallization that occurred in a di- rectional manner. Fan et al. 17,18 have performed electrical pulse treatments on magnesium alloys and found that the non-thermal effect of the pulsed current can promote ma- terial recovery and recrystallization at a lower tempera- ture. Jeong et al. 19 investigated the tensile deformation of an extruded AZ91 magnesium alloy under the action of a pulsed current by performing standard-tensile in addition to pulsed-tensile experiments at room temperature and 70 °C. The results showed that the Mg 17 Al 12 phase was significantly reduced in the tensile specimens treated by an electric pulse when compared to the samples without any electric-pulse treatment. The pulse current promoted Materiali in tehnologije / Materials and technology 58 (2024) 2, 113–120 113 UDK 546.46:629.5.017.22 ISSN 1580-2949 Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 58(2)113(2024) *Corresponding author's e-mail: gengguihong@nmu.edu.cn (Guihong Geng) dissolution of the Mg 17 Al 12 phase in the extruded AZ91, which improved the overall performance of the alloy. Indhiarto et al. 20 performed unidirectional tensile experi- ments on AZ31B by applying pulsed currents with dif- ferent peak-current densities at the same temperature. The results revealed that the ultimate tensile strength de- creased with increasing peak-current density, independ- ent of the temperature, demonstrating a non-thermal pos- itive effect of the pulsed current on the tensile properties. Currently, the evolution of the tissue properties of the pulsed-current-induced deformation of magnesium al- loys has not been sufficiently studied. There is relatively little research on the electroplasticity of magnesium al- loys and the effect of electric pulse on the alloy during processing. This has hampered the application of elec- tric-pulse-rolling magnesium alloy technology. In this study, the effects of different pulse output volt- ages on the structure and properties of an AZ91D mag- nesium alloy rolled using electric pulses have been inves- tigated. The results generated are significant in advancing the electroplasticity of magnesium alloys and the production practice of electric-pulse rolling. 2 EXPERIMENTAL MATERIALS AND METHODS 2.1 Experimental materials The cast AZ91D magnesium alloy was selected as the test material, and the main components are shown in Table 1. Samples were completely annealed at 400 °C for 3h, with air cooling before use. The AZ91D alloy samples were cut into (60×12×3) mm experimental plates using wire cutting. Table 1: Main components of the AZ91D magnesium alloy Element Al Zn Mn Si Cu Mg w/% 9 0.67 0.25 0.05 0.015 Allowance 2.2 Experimental methods The experiments were conducted at five output volt- ages (0 V (no electrical pulse applied), 100 V, 200 V, 300 V and 400 V) for the single-pass, large-depression (20 %) electric-pulse rolling of AZ91D; the rolling pa- rameters are shown in Table 2. An infrared temperature gun was used to measure the temperature of the sample when it entered and exited the roll, and an oscilloscope was used to monitor the output current of the pulse power supply. The microstructure and mechanical prop- erties of the AZ91D samples rolled under the five differ- ent output-voltage conditions were analyzed. The experimental tests used strong-pulsed-current rolling equipment developed in our laboratory, and is composed of two parts: rolling equipment and a strong-pulsed-power supply. Pressure sensors on the rolls displayed the pressure between the upper and lower rolls in real time; the strong-pulse rolling equipment and the working principles are illustrated schematically in Fig- ure 1. Table 2: Rolling parameters Sample number Voltage (V) Fre- quency (Hz) Pulse Width (μs) Current Density (A/mm 2 ) Roll-in tempera- ture (°C) Roll-out tempera- ture (°C) EP0 0 – – – 81 27 EP1 100 600 20 69 77 25 EP2 200 600 20 342 77 26 EP3 300 600 20 364 79 25 EP4 400 600 20 410 78 25 2.3 Analytical Testing Analysis of the fracture morphology of the electro- pulsed rolled AZ91D employed a ZEISS-Vert.A1 in- verted metallurgical microscope. The sample micro- structure was evaluated using a ZEISS Sigma 500 thermal field-emission scanning electron microscope equipped with an X-ray energy spectrum analyzer (EDS) and electron-backscatter diffraction (EBSD) at an accel- erating voltage of 15 kV and an optical diaphragm of 60 μm. An HXD-1000TM microhardness tester was em- ployed with an experimental load of 4.9 N and a load time of 15 s. The CMT5305 microcomputer-controlled electronic universal testing machine was used for room- temperature tensile performance testing. 3 RESULTS AND DISCUSSION 3.1 Effect of output voltage on the surface morphology of AZ91D magnesium alloy rolled by an elec- tric-pulse treatment The sample morphology of the AZ91D rolled by an electric-pulse treatment at different output voltages is il- lustrated in Figure 2. It can be seen that the samples EP4 all have fewer surface cracks than EP0, which was not subjected to electric-pulse rolling. The EP0 sample ex- J. FENG et al.: EFFECT OF OUTPUT VOLTAGE ON AN AZ91D MAGNESIUM ALLOY ROLLED USING ... 114 Materiali in tehnologije / Materials and technology 58 (2024) 2, 113–120 Figure 1: Schematic diagram of the strong-pulse rolling equipment and the working principles: a) shows an image of the strong-pulse roll- ing equipment, b) illustrates the strong-pulse power control panel, c) is a schematic representation of the electric-pulse rolling process hibited more fine cracks at the edges with evidence of bending after rolling. There were no obvious defects such as surface cracks on the surface of EP2 and EP3 samples, where the output voltage was 200 V and 300 V, respectively. A small number of edge cracks appeared on the surface of the EP4 sample rolled by an electric pulse at an output voltage of 400 V. As the dense hexagonal crystal structure of the EP0 alloy is resistant to opening, cracks appeared during the rolling process. The EP1-3 samples treated with electric pulses of 100–300 V exhibited a gradual reduction in surface cracking with an improved plastic-forming capa- bility. This can be attributed to the effects of the energy and magnetic field generated by the pulsed current on the dislocation debonding and debonding rate. The induction magnetic field can alter the binding energy of the dislo- cation and the paramagnetic phase from the S state (sin- gle state) to the T state (triple state), so that the disloca- tion is not entangled but can readily detach from the center of the pegging. This effect facilitates the sliding of dislocations on different crystal surfaces, which mini- mizes or eliminates the surface-crack formation. When the output voltage was 400 V in the case of EP4, the ap- pearance of sample cracks during rolling may be due to further dislocation slippage causing dislocation prolifera- tion that results in process hardening. 21 3.2 Effect of output voltage on the electric-pulse roll- ing of the -Mg 17 Al 12 phase of AZ91D magnesium alloy The SEM images of the AZ91D after rolling by elec- tric pulses with different output voltages are shown in Figure 3. It can be seen that the -Mg 17 Al 12 phase in the EP0 sample is distributed in the -Mg matrix as a coarse, irregular, skeleton-like formation grid, with evidence of significant crack formation. The morphology of the -Mg 17 Al 12 phase in EP1 is similar to that of the EP0 sample, but the surface cracks were significantly re- duced. The -Mg 17 Al 12 phase in the EP2 and EP3 sam- ples changed from a coarse irregular skeletal arrange- ment to fine, worm-like formations with a secondary presence of flakes, and no obvious surface cracks. In the case of EP4, the -Mg 17 Al 12 phase exhibits a coarseness and irregular skeletal morphology, but no obvious crack formation. The content of the -Mg 17 Al 12 phase in the AZ91D was estimated from its area share in the SEM images, and the results of the calculations are presented in Fig- ure 4. It can be seen that the -Mg 17 Al 12 phase content decreased from 11.3 % to 8.4 % with increasing output voltage from0Vto300V .Atav oltage of 400 V, the -Mg 17 Al 12 content increased to 10.5%. In the operation of the rolling process at an output voltage of 0V-300V, the introduction of the pulse current caused a dissolution of the -Mg 17 Al 12 phase at a temperature lower than its J. FENG et al.: EFFECT OF OUTPUT VOLTAGE ON AN AZ91D MAGNESIUM ALLOY ROLLED USING ... Materiali in tehnologije / Materials and technology 58 (2024) 2, 113–120 115 Figure 3: SEM images of AZ91D magnesium alloy rolled by electric pulse treatment at different output voltages: a) EP0 sample (0 V), b) EP1 sample (100 V), c) EP2 sample (200 V), d) EP3 sample (300 V), e) EP4 sample (400 V) Figure 2: Sample morphology of AZ91D magnesium alloy rolled by an electric-pulse treatment at different output voltages dissolution temperature (ca. 420°C). This can be attrib- uted to a "thermal effect + non-thermal effect" syner- gism, where the dissolved -Mg 17 Al 12 phase is dispersed in the AZ91D matrix. When the voltage was increased to 400 V, the solid solution in the Mg matrix reached an up- per limit due to the pulse-voltage energy which impeded -Mg 17 Al 12 dissolution, resulting in a gradual coarsen- ing. 22 3.3 Effect of output voltage on the weave of AZ91D magnesium alloy rolled by electric pulse treatment The EBSD images and polar diagrams for the elec- tric-pulse rolling of the AZ91D magnesium alloy at dif- ferent output voltages are shown in Figure 5. It can be seen that the weave strength of the EP0-EP3 samples on {0002} and {1010} gradually decreased in the out- put-voltage range 0–300 V. The weave strength on {0002} decreased from 10.23 in EP0 to 4.98 in EP3. The weave strength on {1010} decreased from 4.03 for EP0 to 1.88 for EP3. On increasing the output voltage to 400 V, the weave intensity on {0002} and {1010} in- creased. At an output voltage of 0–300 V, the pulse cur- rent resulted in a random grain orientation. This response can optimize the dislocation-slip mechanism configura- tion and lower the stress concentration in adjacent grains during the forming process, enhancing the strain coordi- J. FENG et al.: EFFECT OF OUTPUT VOLTAGE ON AN AZ91D MAGNESIUM ALLOY ROLLED USING ... 116 Materiali in tehnologije / Materials and technology 58 (2024) 2, 113–120 Figure 4: Content of the -Mg 17 Al 12 phase in AZ91D magnesium al- loy rolled by electric-pulse treatment at different output voltages Figure 5: EBSD image and pole diagram of AZ91D magnesium alloy rolled by electric-pulse treatment at different output voltages: a) EP0 sam- ple (0 V), b) EP1 sample (100 V), c) EP2 sample (200 V), d) EP3 sample (300 V), e) EP4 sample (400 V) nation between grains and optimizing the magnesium al- loy weave. 23,24 3.4 Effect of output voltage on electrical pulse AZ91D magnesium alloy twinning The EBSD images of marked twin grain boundaries of the AZ91D magnesium alloy rolled by an electric pulse at different output voltages are shown in Figure 6. The red line indicates the {1012} tensile twin grain boundaries, and the calculated statistics for twin content in the EP0-4 samples are presented in Figure 6f. It can be seen that the lowest twin content (6.74 %) occurred in the E0 sample where no electrical pulse was applied. The twin crystal content increased with increasing voltage, reaching a maximum of 14.10 % at 300 V, with a subse- quent decrease to 7.86 % at 400 V. The observed trend of an initial increase in twinning content up to 300 V followed and a decrease at 400 V in- dicates that the electric-pulse rolling has a promotional effect on the twinning of the AZ91D magnesium alloy samples that is optimum at 300 V. This increased twinning served to enhance the plastic-forming capabil- ity of AZ91D. Increasing the output voltage in the range 0–300 V produces a Joule heating effect, and the increase in tem- J. FENG et al.: EFFECT OF OUTPUT VOLTAGE ON AN AZ91D MAGNESIUM ALLOY ROLLED USING ... Materiali in tehnologije / Materials and technology 58 (2024) 2, 113–120 117 Figure 7: Distribution of misorientation angle in AZ91D magnesium alloy during electric-pulse rolling treatment under different output voltages: a) EP0 sample (0 V), b) EP1 sample (100 V), c) EP2 sample (200 V), d) EP3 sample (300 V), e) EP4 sample 400 V) Figure 6: EBSD images of labeled twin grain boundaries of AZ91D magnesium alloy rolled by electric-pulse treatment at different output volt- ages: a) EP0 sample (0 V), b) EP1 sample (100 V), c) EP2 sample (200 V), d) EP3 sample (300 V), e) EP4 sample (400 V), f) twin content as a function of output voltage perature reduces the critical parting stress (CRSS) of the non-basal slip system of the magnesium alloy. More slip systems can then participate in plastic deformation with a resulting increase in the number of twins. When the voltage was increased to 400 V, the injection of excess energy caused the number of twins to decrease. This sin- gle-crystal orientation feature served to promote the mi- gration of twin boundaries under cyclic stress, which led to changes in twin structure and even the disappearance of the twins. 25 3.5 Effect of output voltage on the distribution of small-angle grain boundaries in AZ91D magne- sium alloy rolled by electric-pulse treatment The distribution of the grain-boundary angle orienta- tion differences in the AZ91D magnesium alloy rolled by electric pulse at different output voltages is shown in Figure 7. The content of the small-angle grain bound- aries < 5° in the EP0 sample was 69 %, with peaks ap- pearing at 40° and 86°. At an output voltage of 100 V, the content of small-angle grain boundaries < 5° was lowered to 63%, and the peak at the 40° position was significantly enhanced, while the peak at the 86°position was less intense. When the output voltage was increased to 200 V, the content of small-angle grain boundaries < 5° was further lowered to 62 %, the peak at 40° position was negligible but the peak at 86 was enhanced. At an output voltage of 300 V, the content of small-angle grain boundaries < 5° fell to 61 %, the peak at 40° was no longer present, the peak at 86°was weakened, and a peak at 56° appeared. At an output voltage of 400 V, the content of small-angle grain bound- aries < 5° increased to 68 %, the peak at 40° reap- peared, and the peak at 86° showed a decrease in inten- sity. With an increase of the output voltage, the content of small-angle grain boundaries < 5° in AZ91D first de- creased, then increased and reached a minimum value at an output voltage of 300 V. 3.6 Effect of output voltage on the mechanical proper- ties of AZ91D magnesium alloy rolled by elec- tric-pulse treatment 3.6.1 Effect of output voltage on microhardness The microhardness of each phase of AZ91D magne- sium alloy rolled by electric-pulse treatment at different output voltages is illustrated in Figure 8. It can be seen that the -Mg matrix and -Mg 17 Al 12 phase microhard- ness in EP0 are 58.8 HV and 98.8 HV, respectively. When the output voltage was increased to 100–300 V, the -Mg matrix microhardness gradually decreased to give the lowest value (49.8 HV) at an output voltage of 300 V. The microhardness increased to 56.9 HV at an output voltage of 400 V. The microhardness of the -Mg 17 Al 12 phase gradually increased over the voltage range 100–200 V, giving the highest microhardness (118.8 HV) at 200 V. The microhardness subsequently decreased at an output voltage of 300–400 V to reach a microhardness of 101.7 HV at 400 V. The electrical pulse treatment increases the diffusion rate of metal atoms, and high-energy pulse current re- sults in an electron flow at high speed. This produces a high-frequency periodic impact effect on the atoms in the metal, resulting in a high-energy state that enhances the pulse-current non-thermal and Joule-heat effects. 21 The -Mg 17 Al 12 precipitated phase gradually solidifies into the -Mg matrix at 0–200 V, the -Mg 17 Al 12 phase is re- fined and the -Mg matrix solid solution is strengthened. The refinement and solid solution strengthening effect is more effective at an output voltage of 200V, leading to the highest observed AZ91D microhardness. 3.6.2 Effect of output voltage on tensile properties The average tensile strength and elongation of the AZ91D are presented as a function of output voltage in Figure 9. In the voltage range 0–300 V, the tensile strength of the AZ91D increased to give a maximum ten- J. FENG et al.: EFFECT OF OUTPUT VOLTAGE ON AN AZ91D MAGNESIUM ALLOY ROLLED USING ... 118 Materiali in tehnologije / Materials and technology 58 (2024) 2, 113–120 Figure 9: Tensile properties of AZ91D magnesium alloy rolled by electric pulse treatment at different output voltages Figure 8: Microhardness of each phase in AZ91D magnesium alloy rolled by electric-pulse treatment at different output voltages sile strength of 165 MPa at 300 V. In the case of sample elongation, an increase was observed from 0 to 200 V, with a subsequent decrease in the voltage range 200–400 V. The highest elongation of electric-pulse- rolled AZ91D magnesium alloy samples was 4.1 % at an output voltage of 200 V. Combined with the SEM image analysis, it can be seen that when the pulse output volt- age was 0–300 V, dissolution and refinement of the -Mg 17 Al 12 phase occurred in the magnesium alloy speci- men, and the coarsening of the -Mg 17 Al 12 phase in the matrix served to increase the tensile strength. 26 At a pulse output voltage in the 0–200 V range, an appropri- ate electrical, thermal and stress energy was instanta- neously transmitted to the material and the random ther- mal motion of the atoms generated sufficient kinetic energy to disrupt the equilibrium position with an en- hanced diffusion of atoms and facilitated slipping and climbing of dislocations that extended elongation in AZ91D. 21 The SEM images in Figure 10 illustrate the fracture of the AZ91D magnesium alloy rolled by an electric pulse at different output voltages. When no electrical pulse was applied, there is clear evidence of cracks, de- structive steps and some nest formations that demon- strate sample fracture. When the output voltage was in- creased, the tough nest in the fracture of AZ91D and the form of sample fracture changed from brittle to ductile fracture, with an accompanying improvement of plastic deformation. At a voltage of 200–400 V, the tough nest in the sample fracture decreased with a resultant poorer plastic-forming ability. According to the fixed-point en- ergy-spectrum analysis, shown in Figure 11, the tough nests in the fracture were mainly distributed in the -Mg matrix, while the cracks and deconstruction steps were mainly present in the -Mg 17 Al 12 phase and the -Mg matrix, consistent with the analysis given above. With an increase in the output voltage, the tensile strength and elongation of the AZ91D first increased and then decreased, reaching the highest tensile strength of 165 MPa at 300 V. The greatest elongation of the sample was 4.1 %, achieved at an output voltage of 200 V. From a consideration of the fracture analysis, an increased out- put voltage served to increase the tough nests in the frac- ture of AZ91D, most notably at 200 V. At a voltage in excess of 200 V, the tough nests were observed to de- crease. J. FENG et al.: EFFECT OF OUTPUT VOLTAGE ON AN AZ91D MAGNESIUM ALLOY ROLLED USING ... Materiali in tehnologije / Materials and technology 58 (2024) 2, 113–120 119 Figure 11: Energy spectrum analysis Figure 10: Fracture morphology of AZ91D magnesium alloy during electric-pulse rolling at different output voltages: a) EP0 sample (0 V), b) EP1 sample (100 V), c) EP2 sample (200 V), d) EP3 sample (300 V), e) EP4 sample (400 V) 4 CONCLUSIONS An increase in output voltage resulted in greater sam- ple surface cracking, and the best surface quality was achieved at an output voltage of 300 V. The lowest con- tent of -Mg 17 Al 12 phase in the sample was 8.4% at an output voltage of 300 V. At an output voltage of 300 V, the samples exhibited the lowest weave strength on {0002} and {1010}, the greatest degree of twinning, and the best plastic-forming ability. The microhardness of the -Mg 17 Al 12 phase was highest at an output voltage of 200 V, and the microhard- ness of the -Mg matrix was lowest at an output voltage of 300 V. The maximum tensile strength of the sample was 165 MPa at an output voltage of 300 V. Moreover, the maximum sample elongation was 4.1% at an output voltage of 200 V. Acknowledgement Supported by the National Natural Science Founda- tion of China (52061002) Ningxia Hui Autonomous Region Key R&D Program (2023BDE03007) Graduate Innovation Project of North Minzu Univer- sity (YCX23108) 5 REFERENCES 1 W. Li, K. Deng, X. Zhang, C. Wang, J. Kang, K. Nie, W. Liang, Microstructures, tensile properties and work hardening behavior of Si-Cp/Mg-Zn-Ca composites, Journal of Alloys and Compounds, 695 (2016) 2215–2223, doi:10.1016/j.jallcom.2016.11.070 2 K. Edalati, R. Uehiro, Y. Ikeda, H. Li, H. Emami, Y. Filinchuk, Z. Horita, Design and synthesis of a magnesium alloy for room temper- ature hydrogen storage, Acta Materialia, 149 (2018) 88–96, doi:10.1016/j.actamat.2018.02.033 3 B. Yan, K. Deng, J. Kang, Mechanical and wear resistance properties of (Grp+SiCp)/AZ91 mag-nesium matrix composites, Rare Metal Materials and Engineering, 48 (2019) 2251–2257, doi:10.3390/ ma12071190 4 Y. Liu, Study on the microplastic deformation behavior of TA2 pure titanium assisted by electric- current, Harbin, Harbin Institute of Technology, 1 (2015) 10–12, doi:10.7666/d.D754107 5 Z. Zhao, G. Wang, H. Hou, Y. Zhang, Y. Wang, Effect of pulsed cur- rent on the deformation behavior of 0.27% hydrogen-substituted Ti-6Al-4V alloy, Journal of Materials Research, 5 (2018) 321–326, doi:10.1038/s41598-018-32857-6 6 O. Troitskiy, V. Stashenko, Electroplastic wire drawing: A promising method of production of lightweight wire and cable, Journal of Ma- chinery Manufacture and Reliability, 44 (2015) 758–765, doi:10.3103/S1052618815080087 7 K. Yao, J. Wang, M. Zheng, A research on electroplastic effects in wire-drawing process of an austenitic stainless steel, Scripta Materialia, 45 (2001) 533–539, doi:10.1016/S1359-6462(01)01054-5 8 W. Salandro, C. Bunget, L. Mears, Modeling and Quantification of the Electroplastic Effect When Bending Stainless Steel Sheet Metal//Asme International Manufacturing Science & Engineering Conference, 32 (2010) 591–590 9 A. Jordan, B. Kinsey, Investigation of thermal and mechanical effects during electrically-assisted microbending, Journal of Materials Pro- cessing Technology, 221 (2015) 1–12, doi:10.1016/j.jmatprotec. 2015.01.021 10 M. Yoo, Slip, twinning, and fracture in hexagonal close-packed met- als, Metallurgical Transactions A, 12 (1981) 409–418, doi:10.1007/ bf02648537 11 H. Huang, Study of plastic deformation mechanism and recryst- allization behavior of AZ31 magnesium alloy, Thesis, Qinghua Uni- versity, Beijing, 2014 12 S. Agnew, C. Tomé, D. Brown, T. Holden, S. Vogel, Study of slip mechanisms in a magnesium alloy by neutron diffraction and model- ing, Scripta Materialia, 48 (2003) 1003–1008, doi:10.1016/S1359- 6462(02)00591-2 13 Y. Zhou, W. Zhang, B. Wang, G. He, J. Guo, Grain refinement and formation of ultrafine-grained microstructure in a low-carbon steel under electropulsing, Journal of Materials Research, 17 (2002) 2105–2111, doi:10.1557/JMR.2002.0311 14 Y. Zhou, S. Xiao, J. Guo, Recrystallized microstructure in cold worked brass produced by electropulsing treatment, Materials Let- ters, 58 (2004) 1948–1951, doi:10.1016/j.matlet.2003.11.035 15 X. Wang, W. Dai, C. Ma, X. Zhao, Effect of electric current direction on recrystallization rate and texture of a Cu-Zn alloy, Journal of Ma- terials Research, 28 (2013) 1378–1385, doi:10.1557/jmr.2013.86 16 X. Wang, M. Liu, W. Dai, N. Wu, X. Zhao, Effect of electric current direction on the microstructural evolution and mechanical properties of a cold-rolled Cu–Zn alloy during the phase transformation in- duced by electric current pulses, Journal of Materials Research, 30 (2015) 2500–2507, doi:10.1557/jmr.2015.226 17 H. Zhang, Y. Liu, H. Dong, B. Jin, J. Fan, Microstructure, mechani- cal properties and static recrystallization behavior of the rolled ZK60 magnesium alloy sheets processed by electropulsing treatment, Jour- nal of Alloys & Compounds, 646 (2015) 1–9, doi:10.1016/ j.jallcom.2015.04.196 18 Y. Liu, J. Fan, H. Zhang, W. Jin, H. Dong, B. Xu, Recrystallization and microstructure evolution of the rolled Mg-3Al-1Zn alloy strips under electropulsing treatment, Journal of Alloys & Compounds, 622 (2015) 229–235, doi:10.1016/j.jallcom.2014.10.062 19 H. Jeong, M. Kim, J. Park, C. Yim, J. Kim, O. Kwon, P. Madaka- shira, H. Han, Effect of pulsed electric current on dissolution of Mg17Al12 phases in as-extruded AZ91 magnesium alloy, Materials Science & Engineering A, 684 (2017) 668–676, doi:10.1016/j.msea. 2016.12.103 20 I. Indhiarto, T. Shimizu, M. Yang, Effect of Peak Current Density on Tensile Properties of AZ31B Magnesium Alloy, Materials, 14 (2021) 1457, doi:10.3390/ma14061457 21 C. Han, Study on the mechanism of action of high-energy electric pulse toughening of alloy steel, University of Science and Technol- ogy Beijing, 2023, doi:10.26945/d.cnki.gbjku.2023.000043 22 L. Zhang, Y. Li, Research progress on grain refinement methods for magnesium alloys, Foundry, 68 (2019) 1195–1203, doi:10.3390/ met12081388 23 M. Yuasa, N. Miyazawa, M. Hayashi, M. Mabuchi, Y. Chino, Effects of group II elements on the cold stretch formability of Mg-Zn alloys, Acta Materialia, 83 (2015) 294–303, doi:10.1016/j.actamat. 2014.10.005 24 Y. Tang, W. Huo, L. Dong, W. Zhang, H. Peng, S. Zhang, An ul- tra-high formability at room temperature induced by continually dy- namic micro-nanocrystallization of Mg rare earth alloy, Materials Letters, 339 (2023) 134090, doi:10.1016/j.matlet.2023.134090 25 H. Qiao, S. Agnew, P. Wu, Modeling twinning and detwinning be- havior of Mg alloy ZK60A during monotonic and cyclic loading, In- ternational Journal of Plasticity, 65 (2015) 61–84, doi:10.1016/ j.ijplas.2014.08.010 26 Z. Shan, Microstructure and mechanical properties of AZ-system de- formed magnesium alloy treated with high-density pulse current, Taiyuan University of Technology, 2022, doi:10.27352/d.cnki.gylgu. 2020.002013 J. FENG et al.: EFFECT OF OUTPUT VOLTAGE ON AN AZ91D MAGNESIUM ALLOY ROLLED USING ... 120 Materiali in tehnologije / Materials and technology 58 (2024) 2, 113–120