Current Pulse Treatment Research Articles

Plastic recovery and strength enhancement of pre-deformed AZ31B magnesium alloy using transient strong pulse current

Magnesium alloy components are mainly used in aerospace and automotive fields, but poor deformation ability at room temperature restricts their application in other industries. To address this issue, electrically-assisted technology is employed to enhance plasticity of alloys. However, conventional method weaken strength and intensify surface oxidation of such alloys because of prolonged action of current. In view of the above, pre-deformation (PF) treatment in combination with transient induced pulse current treatment (TIPCT) is proposed in the present work so as to balance between plasticity recovery and strength of AZ31B alloy. The results show that the total elongation of PF sample and the corresponding TIPCT specimen first increases and then decreases with the increase in PF percentage under the same voltage. At the same PF percentage, the total elongation of PF and TIPCT specimens also presents the same trend as the voltage increases. At the same time, the total elongation in PF and TIPCT specimens is greater than that of the as-received sample. The maximum total elongation is achieved at the PF percentage of 16% and the voltage of 6kV, being 35% higher than that in the as-received sample. The improvement in total elongation is due to activation of more non-basal dislocations induced by TIPCT and the appropriate amount of microcracks generated by PF. In addition, the TIPCT process also improves the yield strength even if the PF percentage and voltage are changed. Besides that, the work hardening induced by PF treatment and instantaneous action of TIPCT process are the key factors enhancing yield strength. Moreover, comprehensive mechanical properties of TIPCT sample are found to outperform those after direct pulse current treatment (DPCT) under the same PF percentage. Therefore, the proposed composite process provides a feasible scheme to enhance strength and elongation of Mg sheets.

Using pulse current to tailor hydride networks while improving the strength and plasticity of pure titanium

Interstitial hydrogen atoms in titanium usually deteriorate the mechanical properties of titanium by brittle hydride phase or hydrogen-enhanced localized plasticity. In this study, hydride was used as the second phase to improve the tensile strength and elongation of TA1 pure titanium. The continuous coarse hydride network is precipitated in TA1 pure titanium after the hydrogen-charged. Then pulse current treatment is used to decompose the original coarse hydride network and reduce the size and number of hydride strips. Finally, a small uniform hydride network is formed in TA1 pure titanium. The results of tensile experiments indicate that the tensile strength of hydrogen-charged TA1 pure titanium treated by pulse current increases from the 286.4 MPa to 316.1 MPa and the elongation increases from the 47.6 % to 56.8 %. The improvement of mechanical properties demonstrate that the small and uniform hydrides can significantly improve the mechanical properties of TA1 pure titanium. In hydrogen-charged TA1 pure titanium treated by pulse current, the increment of strength is mainly caused by hard phase hydrides, and the increase in plasticity is attributed to the role of twins in coordinating deformation during plastic deformation. This study manifests that in addition to being used as a temporary alloying element to optimize the microstructure of titanium, hydrogen can also be directly act as a second phase in titanium to improve the mechanical properties.

A new strategy for preparing high strength and high precision diffusion bonding GH536 joints via pulsed current and subsequent heat treatment

GH536 as a typical solid solution strengthened Ni-based superalloy, has been widely used in the preparation of laminated cooling structure. Diffusion bonding, which is highly promising as a joining process in laminated cooling structure, generally requires high strength and high precision. However, the high strength joint fabricated by the conventional hot pressure diffusion bonding (HPDB) often leads to severe deformation of base materials. Here, we developed a new diffusion bonding strategy to overcome this issue in GH536 via pulsed current diffusion bonding (PCDB) and subsequent heat treatment. At low temperature and short time (900 °C/30 min), a joint with a high shear strength of 535 MPa and a low deformation rate of 0.42 % was obtained using the PCDB, and these were 1.60 times and 0.28 times that of the conventional HPDB joint, respectively. Meanwhile, the low bonding temperature and short bonding time hindered the formation and coarsening of carbides, allowing them to be eliminated in a short time heat treatment. The unbonded zones healing, carbide dissolution and recrystallization during heat treatment significantly improved the joint shear strength, and the joint shear strength after heat treatment reached 561 MPa.

Effect of Pulse Current Treatment on Anode Corrosion and Discharge of AZ91 Magnesium Alloy

Effect of Pulse Current Treatment on Anode Corrosion and Discharge of AZ91 Magnesium Alloy

Effect of duty cycle and frequency of pulse current on bidirectional electro-migration rehabilitation

In this paper, a new approach of bidirectional electro-migration rehabilitation (BIEM) using pulse currents was proposed. The effect of the duty cycle and frequency of the square wave pulse current on the BIEM was investigated. The results showed that the desalination efficiency was improved by 10 % with the decrease of duty ratio and frequency. Furthermore, With the increase of duty ratio and frequency, the hydrogen permeation of steel bars decreased by 28.5 %. More uniform desalination efficiency was obtained by using pulse current. The half-cell potential of the rebars was also measured and it was higher for the samples using pulse currents than for those using direct currents, indicating a lower risk of corrosion after pulse current treatment. The pH value of the concrete also increased during the BIEM process.

High-efficiency and low-carbon inactivation of UV resistant bacteria in reclaimed water by flow-through electrode system (FES)

With the increasingly serious shortage of water resources globally, it has been paid more attention on how to secure the biosafety of reclaimed water and other non-traditional water sources. However, the 3 most applied disinfection technics, which are chlorine, ultraviolet (UV), and ozone disinfection, all have their disadvantages of selecting undesired bacteria and low energy utilization efficiency. Electrode disinfection is a promising solution, but the current electrode disinfection process still needs to be optimized in terms of the use conditions of the configuration reactivation. In this paper, we built a flow electrode system (FES). To evaluate the disinfection techniques more precisely, we isolated ultraviolet-resistant bacteria (URB) bacteria from the water of the full-scale water plant and tested the disinfection performance of FES and UV. The inactivation rate, reactivation potential, and energy consumption were analyzed. FES could inactivate 99.99 % of the URB and cause irreversible damage to the residual bacteria. FES could make all bacteria strains apoptosis in the subsequent 24 h of storage after alternating pulse current (APC) treatment, 3 V, within 27.7 s. Besides, the energy consumption of FES is about 2 orders lower than that of UV disinfection under the same inactivation rate. In summary, APC-FES is an efficient and low-carbon alternative for future water disinfection, which could achieve the ideal disinfection effect of a high inactivation rate, no reactivation, and low energy consumption.

Insight into microstructure evolution and mechanical properties of 5 wt% SiC/Al composites by high frequency pulse current treatment

In order to improve the status of stress concentration and anisotropy of the as-rolled SiC/Al composites, high frequency pulse current was employed to modify the microstructure and mechanical property. Results show that the skin effect makes the current concentrate on the surface zone. The high density current makes the static recrystallization of 35.8% occurred under the condition that the surface temperature is much lower than that of recrystallization temperature of Al alloy, and the grain size is refined from 2.52 μm to 2.06 μm. The obvious recrystallization behavior in the surface area indicates that the non-thermal effect plays a dominant role in the pulse current treatment process. As a contrast, subgrains growth and partial recrystallization occurred in the internal region and transition region under the non-thermal effect, resulting in a slight increase in average grain size to 2.78 μm and 2.75 μm. Nano-indentation results show that the micro-hardness and the indention work recovery rate in the surface area reach 2.09 GPa and 39.8%, respectively, which are 48.2% and 29.2% higher than that of the as-rolled composites, which proves that the mechanical properties have been improved comprehensively compared with as-rolled composites.

Regulating the dissolution of brittle nano-precipitated phase in FeCrAl alloy by pulse current to repair aging properties

Usually, heat treatment is required to elevate the entire material to a higher energy state, thereby eliminating harmful precipitates and repairing the mechanical properties of aged materials. However, the energy utilization rate of this high-temperature treatment method is low, and the regulation of precipitates dissolution is overly dependent on temperature. In this study, an efficient and energy-saving pulse current method was used to control the brittle Cr-rich α′ phase dissolution in aged Fe-25Cr-5Al grade alloy (Fe-24.32Cr-5.67Al-0.043C in wt.%). Compared with conventional heat treatment, pulse current treatment significantly reduces the dissolution temperature and activation energy of the precipitate, and as the current density increases, the non-thermal effect promoting brittle phase dissolution becomes more pronounced. This study is of great significance for the microstructure control and performance design of materials using pulsed current.

Influence of non-thermal effect caused by pulse current on AZ31B magnesium alloy deformation

This paper studied the influence of pulse current (PC) on the plastic deformation of pre-deformed AZ31B magnesium alloy. Compared to the sample subjected to no current (NC), the PC sample's fracture strain and uniform strain increased by respectively 21.5% and 10%, while its strength slightly decreased. The fracture strain of the PC sample was equal to that of the as-received sample, while yield strength improved by 56 MPa and yield to tensile strength ratio enhanced by 42%. The non-thermal effect caused by PC induced more dislocation motion, weakened the base texture, inhibited void nucleation, and promoted uniform deformation. These actions were critical factors for improving materials' plasticity. Overall, the comprehensive properties of AZ31B magnesium alloy were significantly enhanced by combining pre-deformation and PC treatment. The findings obtained in this research can be expanded to magnesium alloys.

Effects of Electric Current Pulse Treatment on Phosphide Precipitation Behavior in 304 Stainless Steel

The precipitation behavior of phosphides in melting and solidification of 304 stainless steel under treatment using an electric current pulse (ECP) is studied. The composition and crystal structure of phosphides are confirmed and analyzed via scanning electron microscope and transmission electron microscope (TEM). The results show that the phosphides are composed of Cr, Mn, S, and P in the sample that is quenched at 1773 K without ECP treatment. From the high‐resolution TEM images and selected area electron diffraction, the crystal lattice structure of phosphides is the same as that of Cr3P. Mn and S replace some of the Cr and P in the Cr3P lattice because of the replacement solution. Phosphides are hardly detected in the samples that are treated using ECP. ECP treatment inhibits the formation of Cr3P. Phosphide is mainly presented in the form of CrP4 in the samples that are quenched at 1583 K, which contain a large number of nanoaustenite grains. Meanwhile, ECP treatment inhibits the growth of phosphides because of differences in the conductivity between molten steel and phosphides during solidification. The size of phosphides decreases with an increase in current density.

Study on the Heterogeneous Nucleation Mechanism of SiCp/AZ91 Magnesium Matrix Composites under Pulse Current

SiCp/AZ91D magnesium matrix composites with 30% SiCp were successfully prepared by pulsed current melting in this work. Then, the influences of the pulse current on the microstructure, phase composition, and heterogeneous nucleation of the experimental materials were analyzed in detail. The results show that the grain size of both the solidification matrix structure and SiC reinforcement are refined by pulse current treatment, and the refining effect is gradually more obvious with an increase in the pulse current peak value. Moreover, the pulse current reduces the chemical potential of the reaction between SiCp and Mg matrix, thus promoting the reaction between SiCp and the alloy melt and stimulating the formation of Al4C3 along the grain boundaries. Furthermore, Al4C3 and MgO, as heterogeneous nucleation substrates, can induce heterogeneous nucleation and refine the solidification matrix structure. Finally, when increasing the peak value of the pulse current, the repulsive force between the particles increases while the agglomeration phenomenon is suppressed, which results in the dispersed distribution of SiC reinforcements.

Purification of Cu–Zn melt based on the migration behavior of lead and bismuth under pulsed electric current

The recovery and regeneration of waste brass can alleviate the pressure of ore resource demand, and can also obtain considerable economic profits from the regenerated alloy products. However, excessive lead and bismuth residues in brass will lead to severe high temperature brittleness of the alloy, and chemical separation will complicate the separation process due to the difference in activity between elements. In this study, the physical separation of Pb and Bi from brass was realized by applying pulse current based on the electrical conductivity difference between Pb, Bi and brass melt, overcoming the limitation of using metal activity difference for oxidation refining. For 10 kg melt, the distribution of current line is adjusted by designing current intensity, frequency and electrode position to explore the migration behavior of Pb and Bi in brass melt under the action of pulse current. After pulse current treatment, Pb and Bi accumulate on the surface of the melt, especially at the bottom of the melt, forming a region rich in Pb or Bi. Based on the numerical calculation, Pb and Bi migrate in the direction perpendicular to the current line driven by the current density gradient, and the migration direction is the direction of the current density gradient decreasing. Pulse current separation technology has the characteristics of shortening the recovery steps, green energy saving, which provides a new solution for the difficult recycling of scrap copper and has great commercial value.

Corrosion Wear of Hypereutectic High Chromium Cast Iron: A Review

Hypereutectic High Chromium Cast Iron (HHCCI) is a new type of corrosion-wear-resistant material developed from ordinary high chromium cast iron by increasing the chromium and carbon content and is often used in abrasive environments where wear and corrosion interact. The corrosion wear resistance of the HHCCI is related to the number, size, shape and distribution of carbides and the microstructure of the matrix. This paper reviews the research progress in improving the corrosion wear resistance of HHCCI from various aspects such as primary carbide refinement, heat treatment, deep cooling treatment and alloying, etc. Among the methods of refining primary carbides are modification, semi-solid treatment and current pulse treatment. In addition, we also analyze the potential of Cr, V, Nb, Mo, Mn, W, Ni, Cu, Si, N and other alloying elements to improve the corrosion wear resistance of HHCCI. The mechanism for improving the corrosion wear resistance of HHCCI is also explored in depth and research contents worthy of attention are proposed to further improve the corrosion wear resistance of HHCCI. In the future, the author believes that modification + alloying + heat treatment is the most potential application method to improve the corrosion wear resistance of HHCCI. The corrosion wear resistance of HHCCI can be further improved by refining the primary carbide (such as adding rare earth, Ti and other modified elements) + heat treatment (with cryogenic treatment) to improve the strength + alloying (such as adding low-cost, high-potential alloy elements such as N and Si) to improve the corrosion wear resistance of the matrix.

Effects of pulse current and rolling synergistic treatment on properties of Fe85P11C2B2 amorphous alloy

To avoid annealing embrittlement and annealing-induced resistivity drop, the Fe85P11C2B2 amorphous alloy was treated by pulse current (PC) and rolling. PC processing can enhance the mobility of atoms, leading to the formation of α-Fe nanocrystals and the release of internal stress, which increases the saturation magnetization (Ms) and reduces the coercivity (Hc). Rolling after PC treatment will improve the resistivity (ρ) of the sample. The Ms of the sample increases from 1.54 T to 1.64 T, the resistivity enhances from 177.1 μΩ·cm to 192.0 μΩ·cm, and the Hc decreases from 6.4 A/m to 5.6 A/m through the synergistic treatment (PC + rolling). The treated sample maintains good bending ductility.

Influence of single-pulse and high-amplitude current on springback and mechanical properties of AA5052 aluminum alloy sheets

Springback is a key challenge in quasi-static (QS) stamping, which seriously affects the forming accuracy of aluminum alloy. A multi-pulse and low-amplitude current is widely used to reduce the springback of aluminum alloys. However, the increase in workpiece of current severely affects the material performance. Herein, a single-pulse and high-amplitude current is employed to eliminate springback of V-shaped parts in a short time (<500 μs). With an increase in discharge voltage, the springback of V-shaped parts decreases. Compared with QS stamping, the average values of yield strength and tensile strength decrease by 9.2% and 1.2%, while the average values of elongation increases by 18.9% after discharge under 10 kV. The increase in temperature of tensile specimen is found to be 5.6 °C at 10 kV. Thus, the thermal effect caused by a pulse current renders a small influence on the properties of V-shaped components. Moreover, the texture and microstructure before and after discharge are studied using electron backscattered diffraction electron backscattered diffraction and transmission electron microscopy measurements. Briefly, the grain size increases and texture strength decreases under the influence of pulse current. Also, dislocation entanglement at grain boundaries is reduced, compromising the strength and springback effect. This study provides experimental and theoretical bases for eliminating springback of Al alloys with a large pulse current. • The springback of the V-shaped parts is completely eliminated in the presence of pulse current, corresponding to a discharge voltage of 10 kV. • The influence of single-pulse and high-amplitude current on the material mechanical properties and microstructure is analyzed. • The yield strength and tensile strength decrease after discharge treatment, whereas the elongation increases. • After pulse current treatment, the proportion of low-angle grain boundaries (LAGBs) decreased, as well as the dislocation density at grain boundaries and intercrystalline regions was reduced.

Effect of pulse current treatment on interface structure and mechanical behavior of TA1/304 clad plates

To ensure the as-rolled clad plates have good machinability, annealing treatment is an effective method to control the microstructure and mechanical properties of titanium/steel clad plates after rolling. For the traditional annealing, the interface structure is seriously deteriorated after 2–3 h annealing treatment. Here, we report a new method of pulse current assisted treatment in short time after rolling. The influence of current density and treatment time was systematically studied. The degree of recovery and recrystallization of matrix as well as the thickness of the interface reaction layer increases with the increase of current density and treatment time. Finally, after 25.30 A/mm2 and 1 min pulse current treatment, the titanium/steel clad plates has good comprehensive property with an elongation of 48% and tensile strength of 737 MPa. It can be attributed that the dislocation density of the matrix decreases rapidly in a short time under the action of pulse current and the intermetallic compounds (IMCs) are rarely formed. This discovery can greatly improve the efficiency of clad plate treatment after rolling and reduce production costs.

Effect of Extremely Low Frequency Pulse Current Treatment on the Mechanical Properties of Al-Zn-Mg-Cu Aluminum Alloy

Effect of Extremely Low Frequency Pulse Current Treatment on the Mechanical Properties of Al-Zn-Mg-Cu Aluminum Alloy

Investigation on improved micro-formability and forming mechanism under high strain rate of H62 brass in pulsed current-assisted laser impact micro-forming

An innovative processing technology called pulsed current assisted-laser impact micro-forming was proposed to further improve the forming quality of microparts under a high strain rate. The experimental results showed that compared with the traditional annealing heat treatment, the pulsed current treatment significantly improved the formability of H62 brass under laser impact, and the enhancement amplitude increased with increasing pulsed current density. After the pulsed current treatment, the forming depth of the micro-parts under laser impact significantly improved, the necking phenomenon at the transition corner and the bottom of the microgroove was significantly alleviated, and the surface roughness of the micro-parts was effectively reduced. The microstructure of samples was also analyzed by transmission electron microscopy, electron backscattering diffraction, and other advanced characterization techniques. It was found that pulsed current pretreatment can further improve the micro-formability of materials under high strain rate by enhancing the inertial effect of materials, refining grains, and reducing the surface texture density evolution rate.

Refined microstructure and dispersed precipitates in a gradient rolled AZ91 alloy under pulsed current

Pulse current assisted treatment has gained more attention in metallic materials, which is efficient and energy-saving, as compared with traditional heat treatment. However, the microstructural evolution of magnesium alloys with varied pre-deformation under pulsed current is still unclear. In this work, AZ91 alloy is subjected to gradient rolling and pulse current treatment (∼40 s). After gradient rolling, a transition zone from the initial to deformed microstructure was obtained in the sample, and the evolution of phases and twins can be analyzed precisely and continuously. Due to the difference in the Joule heat distribution of pulse current, a large number of fine Mg17Al12 phase are precipitated and dispersed, the precipitation and dissolution process of Mg17Al12 phase occur simultaneously. The region with moderate deformation has the largest recrystallization fraction, and the {101¯1}−{101¯2} double twins and {101¯1} compression twins are the preferred nucleation sites in the early stage of pulse current treatment. The weaken of texture is due to the newly formed grains with non-basal orientations. This work provides a new insight into the microstructural control of pre-deformed magnesium alloys under pulse current assisted treatment.

Formability and mechanism of pulsed current pretreatment–assisted laser impact microforming

Pulsed current treatment was introduced into the laser impact microforming technology to improve the formability of laser impact forming. A pulsed current pretreatment–assisted laser impact microforming technology is proposed, and the formability and mechanism of such composite technology are discussed. In this study, the mechanical properties of H62 brass before and after pulse treatment were tested. The effect of pulsed current treatment on the formability of the material under high strain rate was studied by a laser impact free microbulging experiment. Moreover, the mechanism of pulsed current influence on the material’s formability was analyzed from the aspects of microstructure, texture evolution process, and grain size and morphology. Results showed that the elongation of the material was increased obviously, the flow stress during the tensile process was decreased significantly after pulsed current treatment, and the fracture form of the material gradually evolved from brittle fracture to ductile fracture. The forming height of samples under high strain rate improved greatly which may be due to the high-density pulsed current treatment that significantly alleviated the dislocation entanglement in the material. Owing to the weaker orange-peel effect which is induced by smaller recrystallized grains and lower maximum density of texture, the surface quality of formed parts after pulsed current treatment increased remarkably. In addition, the more uniform section thickness distribution of formed parts was observed, which may stem from obviously refined grains after pulsed current treatment improved the fluidity of the grains in a high–strain rate deformation process.