Effect Of Electropulsing Treatment Research Articles

Rapidly induced homogenization and microstructure control of Cu–15Ni–8Sn alloy by electropulsing treatment

The homogenization heat treatment is a key procedure to controlling the second phase, enhancing composition uniformity and workability of as-cast Cu–15Ni–8Sn alloy. Nonetheless, high annealing temperature and long holding time result in high energy consumption, high costs and severe oxidation. The effects of electropulsing treatment (EPT) and conventional homogenization treatment (CHT) on the microstructure and mechanical properties of Cu–15Ni–8Sn alloy by downward continuous casting were studied. The results showed that with increase of pulse current density, the treatment temperature of the alloy increased continuously. Subsequently, γ-(Cu, Ni)3Sn phase and lamellar (α+γ) phase underwent progressive spheroidizaiton and dissolution. Compared with CHT, EPT contributes to significant reductions in both treatment temperature (about 100 °C) and treatment time (1/34 of the CHT), the tensile strength decreased from 437 Mpa (as-cast alloy) to 380 MPa, while the elongation increased dramatically from 9.2 % to 41.6 %. Compared with being treated by CHT, the alloy treated by EPT performed excellent comprehensive mechanical properties. The extra free energy provided by EPT diminishes the thermodynamic energy barrier of γ phase dissolution and significantly accelerates atomic diffusion, which mainly contribute to rapid homogenization of Cu–15Ni–8Sn alloy by EPT at lower temperature. EPT can work as a novel homogenization heat treatment process for metallic materials, boasting advantages such as high efficiency, low energy consumption and low costs.

Rapid Spheroidization Process of S Phase (Al2CuMg) in the As-Cast 2024 Al Alloy Induced by High-Energy Electropulsing.

The effect of electropulsing treatment (EPT) on the microstructure of the as-cast 2024 Al alloy at room temperature was investigated. The results show that EPT remarkably accelerated the spheroidizing of second phase (S phase) in the as-cast 2024 Al alloy. The mechanism for rapid spheroidizing of the second phase was proposed based on not only the accelerated dissolution, but also the growth of particles. The morphology and size of the secondary phase could be controlled by changing the cooling speed of the specimen after EPT. Furthermore, the dissolving process of the randomly distributed S phase was recognized as the combination effect of the two basic dissolving ways. Hence, the EPT can be applied to improve the microstructure and properties of the alloys.

Superior mechanical properties of M35 high-speed steel obtained by controlling carbide precipitation and distribution via electropulsing treatment

Carbide precipitation and distribution always significantly affect the mechanical properties of High-speed Steel (HSS). Thus, the effect of electropulsing treatment (EPT) on the microstructure and mechanical properties of M35 HSS was investigated in this paper. The results show that the electropulsing austenitising then quenched, followed by electropulsing tempered (EQ + ET) samples, showed a 2.3% increase in Rockwell hardness, a 9.7% increase in the bending strength, and the impact toughness increased by 10.3% compared with the conventional heat treatment (CQ + CT) samples. The superior mechanical properties were attributed to the reduction of retained austenite (RA), the uniform distribution of the carbide, and the refinement of the prior austenite grains. Under the action of the current, Ms increased in response to various combinations of alloying elements, thereby reducing the content of RA. Compared to conventional heat treatments, the electropulsing treatment provides additional Gibbs free energy, as well as a large number of dislocations generated by the thermo-compressive stresses, which increase the carbide nucleation sites, resulting in a large number of small-sized carbides precipitating and uniformly distributed in the matrix. The fracture morphology indicates that micro-cracks arise between the carbide and martensite, and the larger carbide provides a preferential path for crack initiation.

Effect of electropulsing treatment on the precipitation behavior of MnS in sulfur-containing microalloyed 49MnVS3 steel

An experimental investigation has been conducted with respect to the influence of electropulsing treatment (EPT) on the 2D and 3D morphologies, distribution, number and size of MnS precipitates in the high-sulfur micro-alloyed 49MnVS3 steel. After the application of electric current pulse with a peak pulsed voltage of 30 V, the microstructure was refined due to the increasing nucleation rate of particles in liquid steel. Moreover, compared with the untreated steel with spherical MnS randomly distributed in the matrix, the MnS precipitates moved directionally to aggregate on the bottom and top surfaces of the ingot in order to minimize the free energy of the system in case of EPT. For untreated steel samples, the number of MnS was 409 (bottom), 579 (middle) and 437 (top), while that of the treated samples were 226 (bottom), 38 (middle) and 224 (top) in the scanning area of 2.65 × 107 µm2 with ASPEX. The number of MnS with small size decreased while the large-size MnS increased with the application of EPT.

Effects of electropulsing treatment on the microstructural evolution of hot-rolled TiBw/TA15 composite billet with a network architecture

The use of resistance heating patterns is one of the underlying opportunities for the hot processing of hard-working materials. Here, the effect of electropulsing treatment (EPT) on the microstructure of a hot-rolled TiBw/TA15 composite billet with a network architecture was investigated. Experimental results showed that the stable temperature platform presented a competition between Joule heat and heat dissipation, including heat conduction, convection, and radiation, and the temperature distribution was non-uniform. The ultimate temperatures of the EPT samples increased gradually as the electropulsing increased. Then, the traditional heat treatment sample was compared with the EPT samples via electron backscatter diffraction, scanning electron microscopy, and X-ray diffraction. Results of analyses indicate that the athermal effect independent from electropulsing can promote the growth of grains, but it also decreases the dislocation density and increases the recrystallization fraction. Therefore, athermal effects can exist authentically in contrast to the thermal effects, and specific thermal effects can hardly achieve the results obtained in this study.

Effect of electropulsing treatment on microstructure and mechanical properties of Cu–20Ni–20Mn alloy

The microstructure evolution and mechanical properties changes of the deformation-aged Cu–20Ni–20Mn alloy during electropulsing treatment (EPT) were investigated. The results indicate that, compared with the deformation-aged Cu–20Ni–20Mn alloy with a tensile strength of 942 MPa and an elongation of 1.4% in the previous study, the tensile strength and elongation of the deformation-aged Cu–20Ni–20Mn alloy after EPT with je (the root-mean-square value of pulse current density) of 10.7 A/mm2 for 150 s increased to 950 MPa and 11.3%, respectively. Fine recrystallized grains, local high density dislocation tangles and local uniformly distributed θ-MnNi phases were found in the microstructure of alloy after EPT, which played a key role in improving the strength and ductility of alloy simultaneously. The θ-MnNi phases distributed in the vicinity of dislocation tangles were more preferentially dissolved into the α-Cu matrix under the thermal effect and athermal effect of EPT than the θ-MnNi phases at grain boundaries. The kinetic energy from electron momentum (athermal effect) provided by EPT, which triggered the atomic diffusion accompanied by dislocation movement, leading to the acceleration of recovery, recrystallization processes of alloy and the dissolution of θ-MnNi phases. The results provide guidance for the strength-ductility simultaneous enhancement of various metallic materials.

Effect of electropulsing on anisotropy in strength of laser metal deposited Ti−6Al−4V alloy

The effect of electropulsing treatment on microstructure and mechanical strength of laser metal deposited Ti−6Al−4V alloy was investigated in order to eliminate the anisotropy in strength of laser metal deposited Ti−6Al−4V alloy by tensile tests, optical microscopy, scanning electron microscopy, electron back-scattered diffraction analyses and transmission electron microscopy. With increasing applied voltages from 0 to 130 V, the evolution of microstructure within columnar β grains followed the sequence of α′ martensite → colony α structure → basket-weave α structure. The electropulsing treated at 130 V weakened the texture of martensite within β grains. The as-built Ti−6Al−4V alloy showed an anisotropy in yield strength (6.2%). After processing at 130 V, the anisotropy in yield strength was reduced to 0.6%, which was attributed to the almost equivalent distribution of Schmid factor in the samples deformed along different orientations.

Effect of electropulsing treatment on the recovery of AZ31B magnesium alloy

Electropulsing treatment (EPT) is a potential annealing method with advantages of performance improvement and equipment simplification. In the current paper, the effect of EPT on the recovery of AZ31B magnesium alloy during a two-stage plastic deformation process was studied. The tensile properties, residual stress, microstructure, and recovery kinetics were evaluated. The residual stress decreased and the cumulative elongation increased slightly, whereas the yield strength retained relatively high after EPT. A typical recovery process was observed. Moreover, the recovery kinetics was accelerated by the improved pulse current density, which led to lower residual stress and higher cumulative elongation. Thus, satisfactory recovery can be achieved by adjusting the pulse current during EPT. Analysis of the full width at half maximum (FWHM) and kernel average misorientation (KAM) indicated that the dislocation density decreased after EPT. Therefore, the pulse current has a significant impact on the dislocation mobility and annihilation, accounting for the recovery behavior of AZ31B magnesium alloy. A model of the recovery kinetics was established to demonstrate the effect of the pulse current on recovery evolution in AZ31B magnesium alloy.

Accelerated solid solution and aging induced by electropulsing in Mg-Al-Ca-Mn alloy

The effects of electropulsing treatment (EPT) and conventional heat treatment on the microstructure and mechanical properties of extruded Mg-1.18Al-0.3Ca-0.46Mn alloy were investigated.The results showed that EPT can replace the solid solution treatment, refine the grains and reduce 33% of the followed peak aging time (compared with the T6 sample). The mechanism of accelerated aging process may mainly base on the fact that EPT induce more vacancies and dislocations, which makes it easier to nucleate than traditional solid solution treatment. This interesting result exhibits a new pathway to strengthen Mg alloys in a very short time.

Superior dehydrogenation performance of Mg-based alloy under electropulsing

As a feasible technological approach to promote the global energy transformation, hydrogen energy has gradually become a hot topic in the world's energy field. In order to solve the problem of the poor dehydrogenation kinetic performance in solid hydrogen storage materials, the effect of electropulsing treatment on the dehydrogenation kinetic performance of magnesium alloy was studied through the analysis of dehydrogenation amount, dehydrogenation rate, phase composition and microstructure. After electropulsing treatment, the initial dehydrogenation temperature was reduced by 39 °C, and the maximum dehydrogenation rate was increased from 7.48 wt.% H2/h to 14.36 wt.% H2/h. The electropulsing treatment provides a new idea and method for improving the dehydrogenation kinetic performance of hydrogen storage materials.

Anisotropic Electroplastic Effects on the Mechanical Properties of a Nano-Lamellar Austenitic Stainless Steel

Effects of electropulsing treatment (EPT) on the microstructural evolution and mechanical properties of a cold-rolled 316L austenitic stainless steel with nano-lamellar structure were investigated. The EPT experiments were carried out with the electric current direction along the rolling direction (RD) and the transverse direction (TD) of the samples, respectively. Significant anisotropic electroplastic effects for the RD and TD specimens, i.e., reduced hardness/strength and enhanced ductility, were obtained owing to the different recrystallization behaviors of the RD and TD specimens during EPT. The RD specimens after EPT with larger recrystallized grain size and higher volume fraction of recrystallization show lower strength and higher elongation than that of the TD specimens. The main reason might be attributed to the change of the current direction in the two kinds of samples, which results in the different sensitivity of the microstructures to thermal and athermal effects during EPT.

Plasticity and size effects of micro-forming sheet processed by electropulsing

ABSTRACT Commercial sheets need effective pretreatment to eliminate work hardening and anisotropy, and improve their forming properties to meet the requirement of micro-forming process. Compared with the traditional heat treatment, the electropulsing treatment (EPT) process has some advantages of performance improvement and consumes less energy and is environmentally friendly. It is a potential pretreatment method or process for sheets of micro-forming. In this paper, the effect of EPT on copper sheets with varying thicknesses and different grain sizes is studied. Electropulsing can significantly improve the plasticity of cold-rolled sheet, and plasticity improvement effect was better than that of heat treatment. The mechanical properties of copper sheets with different thicknesses which undergo electropulsing show the same size effect as that of samples without electric pulse. After EPT of copper sheets with different grain sizes, the flow stress difference decreased, which weakened Hall-Petch effect. As the thickness of copper sheets decreased, the threshold of current density for plasticizing effect increased. Based on the analysis of the dislocation motion induced by electropulsing, the mechanism of electropulsing to improve the plasticity of copper sheet was presented, which provides a reference for future research on the pretreatment process for micro-forming materials.

Effect of electropulsing treatment on solidification behavior of spring steels in a continuous casting mold simulator

An electropulsing-assisted mold simulator technique was developed to investigate the effects of a pulsed electric voltage on the quality of spring steels during continuous casting by analyzing the mold flux film, shell surface profile, shell microstructure and inclusion distributions. The results revealed significantly increased crystallization fraction of the mold flux film from 61.2% to 75.3% and finer crystalline phase morphology in the case of electropulsing treatment. The surface of the initially solidified shell could be effectively healed, resulting in smoother shell surface profiles with higher pulsed voltage from 0 to 30 V. Furthermore, an increase in the pulsed voltage from 0 to 30 V resulted in finer dendritic structures during solidification with decreasing secondary dendrite arm spacing from the values of 17.6–32.2 to 9.7–15.0 µm in the direction of shell side toward melt side. In addition, an area scan analysis of inclusions in the as-cast spring steel samples showed that the number of MnS inclusions in the size range of 2.0–4.0 µm gradually decreased from 836 to 114 and the number of Al2O3 inclusions in the same size range decreased from 144 to 39, as the voltage increased from 0 to 30 V.

Corrosion Behavior of an AISI/SAE Steel Cut by Electropulsing.

The effect of electropulsing treatment (EPT) on the surface general corrosion behavior of an AISI/SAE 1045 steel under different machining regimes is studied. In the study, the following variables are alternated: high-speed steel (HSS) vs. hard metal (HM), and with and without the assistance of high-density electropulses. The corrosion rates are determined using comparative studies such as gravimetric analysis, salt spray chamber test, electrochemical polarization curve techniques (PC), and linear polarization resistance (LPR). Differences in surface microhardness were evaluated by applying optical microscopy and planimetric procedures. Specimens subjected to electropulses and turned with HM reported greater reductions of corrosion rates. Changes in corrosion behavior can be explained in terms of grain shape factor h variation. The present study demonstrates that electropulsing affects the corrosion behavior of AISI/SAE 1045 steel after the turning process.

EBSD study of the effect of electropulsing treatment on the microstructure evolution in a typical cold-deformed Ni-based superalloy

Evolution of grain structure and grain boundary character distribution in a cold-deformed Ni-based superalloy during the electropulsing treatment (EPT) was investigated by EBSD technique. Compared with the conventional heat treatments (CHT), the nucleation and growth of SRX grains were significantly accelerated by EPT, which was mainly attributed to the high mobility of dislocations and solute atoms, and the efficient energy transfer under the effect of EPT. Especially, with the introduction of electric current, the activation energy of dislocation motion could be reduced by generating additional energy near the dislocation line, which made the motion of dislocation easy to start. The dislocations would also be easy to move in the form of slipping and climbing, under the effect of electron wind force. On the other hand, most of Σ3 boundaries were newly formed through growth accidents in the form of coherent Σ3 boundaries during EPT, and the mutual interactions between different Σ3n (n = 1, 2, 3) boundaries were rather limited. In addition, EPT could indirectly promote the formation of Σ3 boundaries by accelerating the SRX process, but the formation of Σ9 and Σ27 boundaries was inhibited at the temperatures higher than 700 °C. Moreover, the connectivity of random boundaries in the cold-deformed alloy treated by EPT was also discussed.

Microstructure and formability of AZ31B magnesium alloy sheet under continuous pulse current

ABSTRACTUtilising electropulsing treatment (EPT) to improve the formability of metals is of paramount importance for engineering applications. The effects of EPT on the microstructure and formability of AZ31B magnesium alloy sheet were investigated. The results indicated that the microstructure and mechanical properties were slightly improved with the increase of current density, while the formability was promoted distinctly. Besides, the formability of the specimen after EPT was better than that of the specimen annealed at the same temperature, which indicated that pulse current can effectively increase the formability of the sheet. Further studies confirmed that the athermal effect caused by the pulse current made great contribution to the dislocation mobility and improved the formability of the sheet.

Voids healing and carbide refinement of cold rolled M50 bearing steel by electropulsing treatment

The voids caused by the cold rolling (CR) quite deteriorates the final performance of M50 bearing steel. In this work, the effect of electropulsing treatment (EPT) on the voids has been investigated, finding that the nano-size voids around carbides have been extensively healed. Moreover, it is interesting to find that the Cr-rich carbides are partially dissolved and consequently refined by EPT, which could be attributed to the decreased thermodynamic dissolution barriers and accelerated kinetic diffusion of carbon atoms towards dislocation. These results inspire people to develop a novel strategy (CR + EPT) to fully take advantage of CR and tailor the carbides size in bearing steels.

Effects of electropulsing treatment on residual stresses of high elastic cobalt-base alloy ISO 5832-7

The electropulsing treatment (EPT) is utilized to adjust the residual stress of high-elastic cobalt-base alloy ISO 5832-7 components. The maximum current density is 1.63 kA/mm2, and the pulse duration is 500 μs. After EPT, the residual stress decreases from 485 MPa to 271 MPa, the tensile strength and elongation increases. Furthermore, the metallographic structure remains identical, and the full width at half maximum (FWHM) of XRD diffraction peak decreases with the annihilation of dislocations. The results show that the Joule heat and electron dragging force by high-density pulse current induces the annihilation of dislocations, which results in the reduction of the micro residual stresses, and hence the macro residual stress decreases based on their definitions given by E. Macherauch.

Declined Fatigue Crack Propagation Rate of a High‐Strength Steel by Electropulsing Treatment

The fatigue crack propagation behavior is a key issue for the service of engineering materials. The effect of electropulsing treatment (EPT) on the growth of fatigue crack in a high‐strength steel (AISI 4340 steel) is investigated. It is shown that the crack propagation rate could be significantly declined via high‐density EPT. The crack features of fracture surface are examined using laser scanning confocal microscopy (LSCM) and scanning electron microscopy (SEM). The crack deviation, local crack‐healing and bridging phenomenon are proposed to be beneficial to lower the crack propagation rate, which should be brought out by the current detour, selective Joule heating, compressive stress, and electrical breakdown phenomenon. All these EPT effects exhibit significant contributions to the improvement of fatigue properties in the widely used high‐strength steel.

Influence of electropulsing treatment on residual stresses and tensile strength of as-quenched medium carbon steel

With the development of the technique of the high energy electric current pulse, the electropulsing treatment (EPT) is used in manufacturing more frequently. The effects of EPT on residual stresses and tensile strength of as-quenched medium carbon steel are investigated by experiments. The results show that EPT can reduce residual stresses, and improve tensile strength of the specimens. With the increase of the current density, the residual stresses decrease, and the tensile strength increases. The increase of the tensile strength is due to the decrease of the residual stresses.