Electroplastic Rolling Research Articles

Dependence of the Formation of the Microstructure in Titanium Alloys on Electroplastic Rolling Modes

Dependence of the Formation of the Microstructure in Titanium Alloys on Electroplastic Rolling Modes

Anisotropy evolution of wide magnesium alloy foils during continuous electroplastic rolling

Anisotropy evolution of wide magnesium alloy foils during continuous electroplastic rolling

The Electric-Thermal Uneven Characteristics Simulation of Wide Mg Alloy Strip and Electroplastic Rolling Experiment

In order to solve the problem of wide magnesium strip uneven deformation in electroplastic rolling, an uneven field measurement device was designed. The device simulates the actual electro-thermal characteristics and provides as even and constant field conditions as possible for high-efficiency wide Mg strip rolling. Firstly, the effect of electrode position and distance on the electric field unevenness of magnesium strip is observed by setting the electric rolling condition, to provide the optimal electrical-thermal field quantity coupling conditions required by electric rolling. Secondly, in order to reveal the changing trend of the transient field in the actual rolling, the three-dimensional electric field of wide magnesium strip are simulated by the finite element method. The results show that the even temperature field and stable stress field required by the EPR of a wide Mg strip can be guaranteed to the greatest extent by setting electric field parameter Online. The case proves that the continuous EPR of Mg strip with a thickness of less than 0.13 mm without heat treatment can be realized by fine control of the EPR process.

Inhibition Behavior of Edge Cracking in the AZ31B Magnesium Alloy Cold Rolling Process with Pulsed Electric Current

To solve the edge crack problem of AZ31B magnesium alloy cold rolling, a strong pulsed electric current was introduced to the cold rolling process. The influence of intensity, frequency, width of pulsed electric current and other parameters on edge cracking of AZ31B magnesium alloy plate cold rolling was analyzed based on the principle of a single variable. According to the experimental results, the assistance of pulsed electric current cut down edge cracking and the inhibition effect increased obviously with larger current parameters. When the parameters of pulsed electric current reached 4800 A, 500 Hz, 50 μs, zero edge cracking was achieved. Statistics of edge cracks, rolling load change, and microstructure analysis showed that the current thermal effect was not obvious and non-thermal effect played a more important role in the rolling process under pulse electric current. Edge cracks initiate at the shear bands. The addition of pulse current increases the number of shear bands and presents a blanket structure. Therefore, the amount of strain experienced by a single shear band decrease, which has a positive effect on inhibiting the formation of edge cracks. Furthermore, electroplastic rolling refines the grains and weakens the basal plane. As the current parameter increases, the hardness of the magnesium strip decreases and the yield and tensile strengths increase.

Electroplastic rolling of refractory metal strips: mathematical modelling of the process

In order to analyze the electroplastic deformation process, the authors developed a mathematical model that simulates strip rolling with high-density electric current going through the deformation zone. The model consists of two main parts: a model for determining the strip temperature beyond the deformation zone; and a model of the deformation zone. The paper describes temperature fields calculated for a tungsten strip rolled out of a 200 μm thick and 200 μm wide workpiece at the electric current power W equal to 0.2 and 0.4 kW and rolling speeds V equal to 8.5, 28 and 50 mm/s. It was established that the maximum temperature of the strip Tmax is reached inside the deformation zone, the length of which is taken equal to the length of the contact arc ld. In the section located at a distance of more than 3·l d before the rolling stand, the temperature of the strip is equal to 25 оC, which corresponds to the ambient temperature. After the rolling stand, the strip cools down due to heat dissipation. How quickly the strip will cool down is dictated by the cooling conditions, rolling speed and strip size. Obviously, a thinner strip transfers heat more intensely. A drastic temperature increase was observed in the deformation zone of the rolling stand. After exiting from the deformation zone, the strip, heated to the deformation temperature, gradually cools down as a result of heat dissipation. The intensity of the lengthwise temperature decrease rises as the rolling speed and the heat transfer coefficient go down. The results obtained with the help of the mathematical model were used to revise the technical data of the electroplastic rolling mill (the spacing between its key components, roll design, rolling speed, electric current density, etc.) and to elaborate recommended thermomechanical rolling regimes for micron thin molybdenum and tungsten strips.

Design high-performance AZ31 ultrathin strip through multi-pass electroplastic rolling without off-line annealing

The influence of the electropulsing parameters including the current density and the frequency, on the rolling force, the microstructure and the mechanical properties of AZ31 strips processed by electroplastic rolling (EPR) were investigated in this study. On the basis, the double grain refinement mechanism, combing the rapid completed static recrystallization refinement (SRX) of AZ31 strip before the roll with the subsequent dynamic recrystallization refinement (DRX) of AZ31 strips at the deformed zone, was put forward in the whole process of EPR. According to the mechanism of double grain refinement, an innovative method of the production of AZ31 ultrathin strip with excellent comprehensive properties is established and verified. The AZ31 ultrathin strip with the thickness of 0.35 mm was obtained at the optimal electropulsing parameters, and the total reduction of 69% can be obtained though only 2 continuous passes without any off-line intermediate heat treatment in the process of EPR; besides, the maximum rolling temperature does not exceed 483 K. It is indicated that the technology of EPR with the high current density of the electropulsing is one of the most potential method to improve the plastic formability of hardly-deformed metals.

Features of the Analytical Method to Determine the Temperature during Electroplastic Rolling

Features of the Analytical Method to Determine the Temperature during Electroplastic Rolling

Tailoring phase composition of a multielement TiZrAlV alloy via electroplastic rolling

• Effect of strain on electroplastic deformed ZrTiAlV alloy was studied. • Martensitic transformation of Ti alloy can be regulated by electroplastic rolling. • Increasing strain enhances the stress-induced martensite transformation and improves the strength. • The optimal mechanical properties of UTS ∼1398 MPa and ε f ∼ 5.77% were obtained at strain 2.28. The TiZrAlV alloy were deformed by electroplastic rolling with strains from e ∼ 1.31 to 2.70, which led to the phase transformation from β phase to α phase and α phase to α˝ phase. The contents of various phases were tailored by rolling strain. As a result, the deformed alloy exhibited an increasing ultimate tensile strength (1286 MPa to 1398 MPa) and failure elongation (4.05% to 5.77%) from e ∼ 1.31 to 2.28. Further increasing the strain to e ∼ 2.70 led to a further increase in strength and a loss in ductility, 1484 MPa and 3.73%. Our work provides an alternative process to improve the mechanical properties of Ti alloys by tailoring various phase compositions and phase transformations.

Analysis of electric current supply circuits to rolls during electroplastic rolling of tungsten microstrips

One of the important problems in the design and operation of the electroplastic deformation mill is the reliability and uniformity of the supply of powerful electric current to the deformation zone. The high density of the electric current and the uneven distribution of it leads to a different manifestation of the effect of electroplasticity along the width of the strip, an uneven temperature field, and as a result, to a decrease in the quality of the finished product. To evaluate various current supply circuits, a discrete model is proposed, in which the work rolls and the rolled strip are presented as combinations of lumped resistances. The model was used when considering four main circuits for supplying electric current to the rolls of the electroplastic deformation strip mill: straight one-sided, diagonal onesided, direct two-sided, diagonal two-sided. For all circuits, formulas were obtained for calculating the electric currents flowing in the center of the strip and along its edges. The dependences obtained using the developed model show that the greatest non-uniform distribution of electric current across the width of the rolled strip occurs with a direct one-sided current supply. At the same time, its undoubted advantage over other options is a simpler design. Diagonal single-sided and both variants of double-sided current supply (according to this model) give the same results. The main disadvantage of these options is the need to supply electric current from both sides of the rolling mill. Regardless of the selected current supply option, it is necessary to minimize the ratio of the electrical resistances of the roll materials and the deformed material. In particular, this can be achieved by increasing the diameter of the work roll, as well as by choosing a roll material with high electrical conductivity. The model for supplying electric current to the work rolls and recommendations for reducing the uneven distribution of current across the width of the strip are used in the design of electroplastic deformation mills.

On the microstructure and tensile behaviour of nanostructured NiTi alloy produced by electroplastic rolling

Electroplastic rolling was employed to produce nanostructured (NS), near-equiatomic NiTi alloy from a coarse grained NiTi nugget (ingot), which was produced using vacuum induction melting, followed by quenching in water from a temperature of 800°C. The microstructure of NS NiTi was characterized using X-ray Diffraction (XRD) and transmission electron microscopy (TEM). XRD analysis revealed that the NS NiTi is predominantly martensitic at room temperature, with less than ≈10 % of the austenite phase. The NS NiTi alloy has an average grain size of ≈36 nm. TEM investigation confirmed the presence of grains that are less than 10 nm in size and no amorphous zones were detected. The NS martensitic NiTi alloy specimens were tested in tension at two different strain rates (10−2 and 10−1 s−1). In contrast to a stress-strain profile expected in a martensitic NiTi alloy, the stress-strain curves show conventional tensile behaviour. The observed UTS was high, around ≈1800 MPa, with a less than usual elongation to failure of ≈6 %. The presence of dimples on the fracture surfaces can be seen in scanning electron microscopy (SEM) images, which is indicative of ductile fracture. The role of grain size in the observed deformation and fracture features is also discussed.

Modeling of self-healing of microcracks in the process of longitudinal electroplastic rolling

Multiscale model to describe the process of self-healing of microcracks in thin metal sheets during longitudinal electroplastic rolling is developed. The simultaneous treatment of a mechanical load and a pulsed high-energy electromagnetic field on the sheet is assumed. Finite element modeling has shown that under certain conditions microcracks and micropores can self-heal partially in the working zone. Impact of external pulsed high-energy electromagnetic field leads to welding of the shores of microcracks by molten metal in their tops, while the length and volume of cracks decrease.

Effect of Strain Rate on Microstructure and Mechanical Properties of Electroplastic Rolled ZrTi Alloy

The effect of strain rate on the microstructure and mechanical properties of ZrTi alloy upon electroplastic rolling (EPR) is investigated. A higher strain rate leads to a higher ductility in the as‐rolled samples but a poorer ductility in the rolled and thermally treated samples while there are no obvious changes in strength in the two kinds of samples. The enhancement in ductility of the as‐rolled samples is attributed to the increase of α″ and β phases with the increase of strain rate. The decrease in ductility of the rolled and thermally treated sample with the increase of strain rate is attributed to the decrease of ω phase. The mechanisms responsible for these evolutions are discussed in detail.

Effects of electroplastic rolling on mechanical properties and microstructure of low-carbon martensitic steel

In this study, low-carbon martensite steel was obtained by rapid quenching and was then subjected to cold rolling and electroplastic rolling with different deformation amounts. The mechanical properties and microstructures of the steel after rolling deformation were compared and analyzed. The results showed that with the increase in the deformation amount, the material strength and hardness of the steel subjected to cold rolling and electroplastic rolling increased, while the elongation decreased. Under the same rolling thickness-reduction amount, the strength (hardness) of the electroplastic-rolled material was slightly lower than that of the cold-rolled specimen, and the elongation was significantly improved. Owing to the various angles between the lath direction and rolling direction, the deformed laths featured different characteristics. Regarding the lath morphology, there were no significant differences between the electroplastic rolling deformation and cold rolling deformation. During the plastic deformation process, the texture exhibited significant rotation; the texture transformed to a relatively more stable {112}<110>, and the steel showed strong ɑ texture and weak γ texture. The {111} <110> texture was the strongest in the γ direction; it is stronger than the {111} <112> texture. The {111} plane of the electroplastic-rolled specimen was significantly higher than that of the cold-rolled specimen. The positive relationship between texture and plasticity was obtained.

Effects of strain and electropulse duration on elastic modulus of TiNi alloy

The elastic modulus of TiNi alloy was tailored by electroplastic rolling deformation and the effects of rolling strain and electropulse duration on the elastic modulus of electroplastic rolled TiNi alloy were systematically investigated. With rolling strain increasing from 0 to 1.70, the elastic modulus decreases from 61 to 30 GPa, which can be attributed to the increase in dislocation density and deformation-induced low modulus B19′ martensite phase. With electropulse duration increasing from 80 to 120 µs, the elastic modulus first decreases due to the volume fraction increase in low modulus B19′ martensite phase and then slightly increases on account of the dynamic recovery of dislocation and reverse martensite transformation resulted from electroplastic effect induced by high-energy electropulse.

On the tensile behaviour of coarse and ultrafine grained NiTi

Ni50.7Ti49.3 alloy of coarse grained (CG) and ultrafine grained (UFG) microstructures were subjected to tensile tests at different strain rates of 10−1 s−1, 10−2 s−1, 10−3 s−1 and temperatures of 25 °C, 50 °C and 200 °C. The CG state was attained by quenching and the UFG state by electroplastic rolling (EPR). Transmission electron microscopy of the UFG Ni50.7Ti49.3 alloy revealed the presence of shear bands and sub-grains. The microstructure after tensile testing revealed the presence of grains and twin planes of the B19′ martensite phase, which indicates that twinning also plays a role in the deformation of the alloy, in addition to crystallographic slip. The effects of grain size, strain rate and temperature on the stress-induced martensite transformation present during the tensile tests are discussed. Serrated flow was observed intermittently in the stress-strain curves of both CG and UFG Ni50.7Ti49.3 alloy for some specific combinations of strain rate and temperature. Serrations observed were not limited to the stress plateau region, which is typically seen in the stress-strain curves of NiTi alloys as a result of phase transformation, but were noticed rather randomly through the entire strain range. This unsteady flow behaviour is also discussed.

Deformation mechanisms and recrystallization behavior of Mg-3Al-1Zn and Mg-1Gd alloys deformed by electroplastic-asymmetric rolling

AZ31 Mg and Mg-1Gd alloys were subjected to electroplastic rolling (ER) and electroplastic-asymmetric rolling (EASR). Due to the additional shear stress in EASR, different deformation behaviors, including twinning, dislocations and DRX, were witnessed in EASR. For AZ31, significant grain refinement was achieved in the EASR sample. The refined grains with weakened texture contributed to the largely enhanced tensile ductility of the EASR sample. While for Mg-1Gd, the formation of extension twins was booming and propagated throughout the EASR sample, which was considered to be attributed to the high participation of non-basal slip during deformation. Extension twins and their related recrystallization strongly influenced the texture evolution and mechanical properties of the EASR sample, so that both the tensile ductility and strength of the EASR sample were improved.

Achieving ultralow elastic modulus in TiNi alloy by controlling nanoscale martensite phase

A low elastic modulus is urgently expected for bio-implant to avoid the harmful stress-shielding effect. Here, by using electroplastic rolling deformation, an ultralow elastic modulus of E ∼29 GPa was achieved in a Ti-50.7at%Ni alloy. The low elastic modulus can be attributed to the existence of nanoscale lamellas of low-elastic modulus martensite phase with a high fraction of 16.2% and the sluggish stress-induced martensitic transformation and reorientation of martensite variants.

Achieving heterogeneous structure in hcp Zr via electroplastic rolling

Heterogeneous structure has been widely used to enhance the poor ductility of high-strength nanostructured materials. However, it is still a challenge to form heterogeneous structures in hard-deformed materials. Here, by using electroplastic rolling and subsequent low-temperature annealing, a heterogeneous structure was formed in the hard-deformed hcp Zr and exhibited a good combination of high strength and good ductility. Its formation can be attributed to the effective microstructure refinement and high deformation energy storage during the electroplastic deformation process. The present study is important for the design and fabrication of heterogeneous structured metals and alloys.

Abnormal texture development in magnesium alloy Mg–3Al–1Zn during large strain electroplastic rolling: Effect of pulsed electric current

Single pass large strain electroplastic rolling (LSER) was conducted on AZ31 alloy, using pulsed electric current of different current densities, to improve the rollability of magnesium alloy sheet. It was found that TD (transverse direction)-split texture developed in the alloy once the current density exceeded a critical value (in the present case 90 A/mm2). Microstructure and texture analysis reveal that deformed grains, rather than the dynamically recrystallized grains, are the major contributor to the overall TD-split texture. Intragranular misorientation axis (IGMA) and viscoplastic self-consistent (VPSC) modeling were employed to analyze the influence of the pulsed electric current on the deformation mechanisms. Prismatic <a> type geometrically necessary dislocations (GNDs) were found to be dominant in the deformed grains of the specimens with TD-split texture. VPSC modeling indicates that the TD-split texture is likely due to the enhanced prismatic <a> activity caused by the electric current. The special athermal effect of the pulsed electric current on the deformation mechanisms makes LSER a promising technique for texture modification in magnesium alloys for improved formability.

Mg–3Al–1Zn alloy strips processed by electroplastic differential speed rolling

The effect of reduction per pass on the mechanical properties, microstructure and texture evolution of Mg–3Al–1Zn magnesium alloy strips processed by electroplastic differential speed rolling has been investigated. With increasing reduction per pass, the mechanical properties of the rolled strips increase. Both the shear effect and the current pulses play an important part in modifying the microstructure and texture by promoting dynamic recrystallisation. During dynamic recrystallisation, nucleus tends to nucleate in the vicinity of the shear bands. And as the progress of dynamic recrystallisation, shear bands are gradually consumed by the newly nucleated grains and become nearly indistinguishable. The athermal effect of current pulses plays an important role in promoting dynamic recrystallisation.