Electroplasticity in the Al_(0.6) CoCrFeNiMn high entropy alloy subjected to electrically-assisted uniaxial tension

Electrically assisted deformation(EAD)was adopted in this work to overcome the shortcomings such as poor formability and easy cracking in the processing of dual-phase the Al_(0.6) CoCrFeNiMn high entropy al-loy(HEA)at room temperature.Electroplasticity of the Al_(0.6) CoCrFeNiMn HEA was studied systematically using electrically assisted uniaxial tension.The results showed that pulse current caused the temperature gradient along the tensile direction and the temperatures of the samples increased with the current den-sity.The flow stress decreased,and the elongation increased with increasing current density during the EAD.When the current density was 30 A mm-2,the total elongation of the samples could be increased by 50%compared to that with no pulse.Pulse current can reduce local stress concentration and post-pone microcracks initiation in the body-centered cubic(BCC)phases,and hence can effectively inhibit cracks and ruptures.The dislocation tangles were opened by pulse current,and the dislocation recovery was enhanced at a high current density.Compared with dilute solid solution alloys,the lattice distortion effect,the high fraction of the BCC phases,and the dislocations in HEAs can lead to the enhancement of the local Joule heating,which accelerated dislocation slip and dislocation annihilation.This study con-firms that EAD can effectively im prove the formability of HEAs and provides theoretical guidance and an experimental basis for forming HEAs components.

Minimizing serrated flow in Al-Mg alloys by electroplasticity

Serrated flow under the influence of electroplasticity in Al-Mg alloys is investigated within the dynamic strain aging interpretations of the Portevin-Le Chatelier effect. The stability of plastic region is extended by the pulsed electric current with the increase of critical strain and the extension of waiting time.Meanwhile, the dislocation density, affecting the plastic instabilities due to the interaction between solute atoms and mobile dislocations, is greatly reduced, which plays a dominant role in the suppression of serrated flow.

Effect of electric pulse rolling on plastic forming ability of AZ91D magnesium alloy

AZ91D magnesium alloy rolled under four rolling conditions,namely cold rolling,electric pulsecold rolling,hot rolling and electric pulse hot rolling,and the first principles calculation of Mg with or without external electric field carried out.The results show that:The application of pulse current in the rolling process of AZ91D magnesium alloy can effectively improve the edge crack of the sample,optimize the texture of AZ91D magnesium alloy and reduce its texture strength,promote the generation of tensile twins and the transition from small Angle grain boundaries to large Angle grain boundaries,and thus improve the plastic forming ability of AZ91D magnesium alloy.Make it more prone to plastic deformation.Compared with ordinary rolling,the microhardness ofα-Mg matrix decreases by 15%.The tensile strength and elongation increased from 137MPa and 3.4%to 169MPa and 4.7%,respectively.The results show that the stiffness of Mg decreases and the Poisson's ratio of Mg increases when the electric field applies.When the B/G value is greater than 1.75,the plasticity of Mg is improved.The fault energy at the base surface of Mg does not change much,while the fault energy at the prismatic surface of Mg decreases obviously,showing the external electric field mainly affects the prismatic surface slip of Mg,which makes the prismatic surface slip easier to start,and thus improves the plastic forming ability of Mg.

Microstructure and texture evolution of Mg–3Zn–1Al magnesium alloy during large-strain electroplastic rolling

Large-strain deformation by single electroplastic rolling （EPR） was imposed on AZ31 magnesium alloy strips. During EPR at low temperature （150-250℃）, numerous twins formed in the alloy. After EPR at a high temperature （350℃）, the number of twins reduced and some dynamic recrystallization （DRX） grains formed at grain boundaries and twinned regions. The synergic thermal and athermal effects generated by electropulsing, which promoted dislocation motion, induced a few small DRX grains, and ductile bandings were mainly re- sponsible for large-strain deformation during EPR. The inclination angle of the basal pole stemmed from the counterbalance of the inclina- tion direction of the basal pole between the DRX grains and deformed coarse grains.

A review of electromagnetic processing of materials(EPM):Heating,sintering,joining and forming

Electricity is an efficient form of energy,and the growing interest in electricity-assisted manufacturing is motivated by its inherent energy saving and reduced environmental impact.Beyond this,Electromagnetic Processing of Materials(EPM)allows the fabrication of materials with new compositions,metastable phases and nanograined microstructures that cannot be obtained using conventional heating processes using furnaces.This review covers EPM for the manufacture of ceramic and metal bulk components,with a specific focus on the effects of electric fields and electromagnetic radiations on processing in a wide spectrum of frequencies ranging from DC(f=0 Hz)to visible light(f=10^(14)–10^(15)Hz).The manuscript is divided into two parts.The first part provides a comprehensive overview of the interactions between matter and electric field/current,including heating phenomena(resistive Joule,induction,dielectric heating,electric arcs)and athermal effects(electromigration,electroplasticity,electrochemical reactions,ponderomotive force and others).The second part is focused on the technological application of the techniques,covering heat treatments,joining,sintering and forming.Seven distinct physical phenomena are involved in EPM:resistive Joule and induction heating,electrochemical reactions,electroplasticity,electric arcs and electromagnetic heating based on radio and microwave frequencies(mainly used for heating dielectric materials;i.e.,dielectric heating)or on the IR/visible light(IR heating and lasers).

Dislocation reconfiguration during creep deformation of an Al-Cu-Li alloy via electropulsing

Creep mechanism was well-known to be mainly dominated by the dislocation sliding and climbing during creep deformation. Here we study the creep deformation of an Al-Cu-Li alloy with the assistance of electropulsing and subsequent microstructural observations. We find that creep strain increased drastically under electropulsing and was almost twelve times as much as that of the non-pulsed sample. Microstructural observations confirmed that dislocation reconfiguration happens via electropulsing, namely helical dislocations being opened rapidly. This opened dislocation structure can possess a much higher mobility than the initial helical dislocation, which mostly responsible for the greatly increased creep strain. Our results revealed a new mechanism accountable for the distinctly electroplastic creep deformation.

Investigation on Two Electrically-Assisted Forming Processes of AZ31B Magnesium Alloy Sheets

Two new types of electrically-assisted forming(EAF) processes of AZ31B magnesium alloy sheets,i.e., electrically-assisted blanking(EAB) and electrically-assisted sheet upset-extruding(EASUE), are proposed in this paper. During EAB, pulsed current(PC) decreases blanking load and improves blanked surface quality,and higher frequency has a more effective improvement;when the frequency reaches 600 Hz, the whole punched hole fracture is improved to smooth zone. Moreover, EAB does not influence the microstructure and does not induce obvious annealing, and this process is advantageous to the materials that cannot change microstructure.During EASUE, PC can reduce extrusion load and enhance extrusion height, and higher frequency also has a more effective improvement. Both processes indicate that introducing PC can effectively improve the part quality and have an application prospection.

Effect of Temperature on the Dynamic Recrystallization of AZ31 Alloy with Pulse Current

The tensile tests of AZ31 magnesium alloy were carried out under room temperature, 100, 150 and 200 ℃ with andwithout pulse current. The effect of temperature on dynamic recrystallization （DRX） of AZ31 alloy was studied at differentconditions. One-parameter approach was used to analyze the critical conditions of DRX, the critical stress was obtainedunder different temperatures, and the related results were validated by metallography observation. The results showed thatDRX of AZ31 alloy occurred at 200 ℃ without pulse current. When pulse current with 150 Hz/50 V parameter wasapplied at room temperature, DRX occurred, while DRX was not completed until temperature over 150 ~C. With theanalysis result of critical conditions of DRX based on one-parameter approach, the relationship between critical stress andpeak stress obtained in this present study is σc = （0.746-0.773）σp.

Residual Stress Removal Under Pulsed Electric Current

The effect of a pulsed electric current on the residual stress evolution of metal materials has been investigated.It was found that the surface and internal residual stresses in the as-quenched samples were reduced dramatically by electropulsing.A large number of experimental data show that the residual stress reduction is proportional to the initial residual stress and related to the material properties and electropulsing parameters.Under the combined actions of drift electrons,Joule heating,and residual stress,the dislocation mobility was enhanced,resulting in plastic strain and the decrease in residual stress.Drift electrons played a unique role in the electropulsing treatment,acting as an additional force pushing dislocations forward.The dislocations ultimately accumulated at a grain boundary,forming a parallel arrangement.Finally,the phenomenological equation of the residual stress evolution under electropulsing was derived from the experimental data.

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 316 L 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.

Uniform texture in Al-Zn-Mg alloys using a coupled force field of electron wind and external load

Cylindrical Al-Zn-Mg alloys were processed by electroplastic compression with forced air cooling.Compared to a simple compression process,an unequal intensity of {110} <111> was obtained,and other textures were eliminated by electroplastic compression,that is,electroplastic compression can promote a uniform texture.The various textures formed in different regions along the radial direction under a simple compression process were illuminated by analyzing the relationship between the crystal rotation and stress state.Furthermore,the interaction between the electrons and dislocations was studied in electroplastic compression.The electrons enhanced {110} <111> by promoting slipping of the dislocations when the Burgers vectors of the dislocations were parallel to the drift direction of the electrons.However,the electrons also inhibited crystal rotation by pinning the dislocations with the Burgers vectors perpendicular to the drift direction of the electrons.Therefore,textures other than {110} <111>have difficulty forming under electroplastic compression.The effect of the current energy on the texture(enhancement or attenuation) was in accordance with the law of conservation.The results provided reasonable explanations for the test phenomena.

Experimental Investigation on Formability of AZ31B Magnesium Alloy V-Bending Under Pulse Current

In this work, the influence of pulse current parameters on springback and bending force of magnesium alloy duringelectropulse-assisted （EPA） V-bending was investigated. The experimental results showed that pulse current can effec-tively reduce the springback and the bending force compared to the experiments without current. The frequency has a moresignificant influence on bending force and springback than electric current density. Electroplastic （EP） effect begins towork when pulse current parameters reach a threshold value. To explore the mechanism of EPA V-bending, themicrostructure evolution and fracture surface of the bending specimen were studied. It was found that pulse current canpromote the occurrence of dynamic recrystallization （DRX） of magnesium alloy compared to traditional hot formingprocess. The fracture mode of AZ31B under EPA V-bending evolves from brittle fracture to ductile fracture withincreasing pulse current parameters. Based on the discussion of athermal and thermal effects of EP effect, the mechanismof pulse current to promote DRX is studied and athermal effect is proved to exist.

Electroplastic Tensile Behavior of 5A90 Al–Li Alloys

The electroplastic（EP） tensile properties of 5A90 Al–Li alloys compared with thermal tension were investigated.The microstructural variation at different conditions was observed by SEM and TEM.The current density significantly influences the elongation and the flow stress.With increasing current density,wider and deeper dimples on the fracture surfaces and less dislocation density and pile-ups in the EP tension samples were observed compared with roomtemperature and thermal tension,which indicates the plasticity improvement and flow stress reduction.The EP effect（EPE） mainly results from a comprehensive function of Joule heating and pure EPE.Among them,Joule heating effect is perhaps a dominant factor.

Features of Electroplastic Effect in Alloys with Martensite Transformation

Influence of different electric current modes （pulse and direct） on occurrence of the electroplastic effect under uniaxialtension in the coarse-grained alloys with martensite transformations is investigated. The materials are shape memoryTi49.3Niso.7 alloy and metastable austenite transformation-induced plasticity （TRIP） steel. The paper contains experimentalresults of current impact on the ＂stress-strain＂ curves of the material. It has been taken an experimental measurement ofthe sample temperature during the test. It is shown that the shape of a stress-strain curves and type of the serrate plasticflow, connected with the martensitic transformation and electroplastic effect, depend on the current modes. Impact of pulsecurrent and direct current suppresses shape memory and TRIP effect.