The Effect of Pulse Electric Current on the Mechanical Properties and Fracture Behaviors of Aluminum Alloy AA5754

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Kunmin Zhao ◽  
Rong Fan
Keyword(s):  
Flow Stress ◽  
Energy Density ◽  
Current Density ◽  
Pulse Current ◽  
Maximum Flow ◽  
Total Elongation ◽  
Electric Currents ◽  
Electrically Assisted ◽  
Heating Effects ◽  
Pulse Electric

The influences of pulse electric currents at energy density levels of 0.105 J/mm3 and 0.150 J/mm3 on AA5754's flow stress and elongation are investigated. Different combinations of current density and pulse duration are carried out for each energy density. The non-Joule heating effects in electrically assisted forming (EAF) are revealed since the temperatures generated by the electric currents of the same energy density are identical. It is observed that a pulse current helps reduce AA5754's flow stress and increase its elongation. At the same level of energy density, as the current density increases, the instant drop of stress increases as well as the elongation, although the maximum flow stress remains almost unchanged. A theoretical model is proposed that can predict the stress drop during electrically assisted forming. The fracture surfaces of AA5754 subject to pulse currents are observed and analyzed. The dimples of fracture continue to decrease until they completely disappear as the density of pulse current increases. The suppression of voids nucleation and growth by a pulse current leads to the increase of total elongation.

Constant Current Density Compression Behavior of 304 Stainless Steel and Ti-6Al-4V During Electrically-Assisted Forming

2011 ◽  
Author(s):  
Joshua J. Jones ◽  
Laine Mears
Keyword(s):  
Stainless Steel ◽  
Flow Stress ◽  
Current Density ◽  
Elevated Temperatures ◽  
Shape Change ◽  
Electrical Current ◽  
304 Stainless Steel ◽  
Constant Current ◽  
Constant Current Density ◽  
Electrically Assisted

A metal forming technique which has more recently come of interest as an alternative to processes that use elevated temperatures at some stage during manufacturing is Electrically-Assisted Forming (EAF). EAF is a processing technique which applies electrical current through the workpiece concurrently while the material is being formed. At present, this method has only been studied on an experimental level in laboratory settings, and the heuristic results show increased fracture strain, reduced flow stress, and reduced springback; the enhanced process capability is beyond the range that would be expected from pure resistive heating alone. Thus far, when applying the electrical current through the workpiece during deformation, the current magnitude flowing through the workpiece has remained constant. Hence, for a compression loading, the current flux or density decreases as a result of an increasing specimen area. This work examines the effect of a non-constant current density (NCCD) and a constant current density (CCD) on the deformation behavior of 304 Stainless Steel and Ti-6Al-4V during uniaxial compression testing. Additionally, the application of a CCD is used to modify existing empirically-based EAF flow stress models for these materials. From this testing, it is shown that a CCD during forming can significantly reduce the flow stress of the material as compared to the NCCD tests. The reductions in the flow stress were increased at higher strains by approximately 30% and 15% for the 304 Stainless Steel and Ti-6Al-4V, respectively. More importantly, these flow stress curves are better representative of how the material responds to an applied electrical current as the specimen shape change is removed from the results. Also, the NCCD tests were approximated using an existing empirically-based EAF flow stress model and the CCD tests concluded that a new flow stress predictor model be introduced.

Analysis and Observations of Current Density Sensitivity and Thermally Activated Mechanical Behavior in Electrically-Assisted Deformation

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
James Magargee ◽  
Rong Fan ◽  
Jian Cao
Keyword(s):  
Flow Stress ◽  
Mechanical Behavior ◽  
Electric Current ◽  
Current Density ◽  
Rapid Heating ◽  
High Strength ◽  
Thermally Induced ◽  
Thermally Activated ◽  
Electrically Assisted ◽  
Wide Range

The flow of electric current through a metal during deformation has been observed to reduce its flow stress and increase its ductility. This observation has motivated the development of advanced “electrically-assisted” metal forming processes that utilize electric current to assist in the forming of high-strength and difficult-to-form materials, such as titanium and magnesium alloys. This method of heating provides attractive benefits such as rapid heating times, increased energy efficiency due to its localized nature, as well as the ability to heat the workpiece in the forming machine thus eliminating the transfer process between oven heating and forming. In this paper, a generalized method is proposed to relate applied electric current density to thermally activated mechanical behavior to better understand and improve the processing of metals during electrically-assisted deformation. A comparison is made of engineering metals studied experimentally as well as in the literature, and it is shown that the method provides insight into what some researchers have observed as the occurrence or absence of a “current density threshold” in certain materials. A new material parameter, “current density sensitivity,” is introduced in order to provide a metric for the relative influence of current density on a material's thermally activated plastic flow stress. As a result, the electric current necessary to induce thermal softening in a material can be estimated in order to effectively parameterize a wide range of advanced electrically-assisted forming processes. Thermally induced changes in material microstructure are observed and discussed with respect to the underlying deformation mechanisms present during electrically-assisted deformation. Finally, a strong correlation between thermally activated mechanical behavior and elastic springback elimination during sheet bending is demonstrated.

Characterization of Flow Stress for Commercially Pure Titanium Subjected to Electrically-Assisted Deformation

2013 ◽  
Author(s):  
James Magargee ◽  
Fabrice Morestin ◽  
Jian Cao
Keyword(s):  
Flow Stress ◽  
Heating Temperature ◽  
Pure Titanium ◽  
Constitutive Models ◽  
Plastic Behavior ◽  
Commercially Pure Titanium ◽  
Coupled Models ◽  
Commercially Pure ◽  
Electrically Assisted ◽  
Tension And Compression

Uniaxial tension tests were conducted on thin commercially pure titanium sheets subjected to electrically-assisted deformation using a new experimental setup to decouple thermal-mechanical and possible electroplastic behavior. The observed absence of stress reductions for specimens air-cooled to near room temperature motivated the need to reevaluate the role of temperature on modeling the plastic behavior of metals subjected to electrically-assisted deformation, an item that is often overlooked when invoking electroplasticity theory. As a result, two empirical constitutive models, a modified-Hollomon and the Johnson-Cook models of plastic flow stress, were used to predict the magnitude of stress reductions caused by the application of constant DC current and the associated Joule heating temperature increase during electrically-assisted tension experiments. Results show that the thermal-mechanical coupled models can effectively predict the mechanical behavior of commercially pure titanium in electrically-assisted tension and compression experiments.

scholarly journals IV. On the heating effects of electric currents. No. III

1888 ◽  
Vol 44 (266-272) ◽  
pp. 109-111 ◽  
Keyword(s):  
Electric Currents ◽  
Heating Effects ◽  
The Law

I have taken a great deal of pains to verify the dimensions of the currents, as detailed in my paper read on December 22,1887, required to fuse different wires of such thicknesses that the law C = ad 3/2 is strictly followed; and I submit the following as the final values of the constant “ a ” for the different metals :—

scholarly journals The study of Zn–Co alloy coatings electrochemically deposited by pulse current

2012 ◽  
Vol 66 (5) ◽  
pp. 749-757 ◽  
Author(s):  
Jelena Bajat ◽  
Miodrag Maksimovic ◽  
Milorad Tomic ◽  
Miomir Pavlovic
Keyword(s):  
Surface Roughness ◽  
Current Efficiency ◽  
Direct Current ◽  
Current Density ◽  
Pulse Current ◽  
Pulse Plating ◽  
Cathodic Current ◽  
Average Current Density ◽  
Corrosion Stability ◽  
Average Current

The electrochemical deposition by pulse current of Zn-Co alloy coatings on steel was examined, with the aim to find out whether pulse plating could produce alloys that could offer a better corrosion protection. The influence of on-time and the average current density on the cathodic current efficiency, coating morphology, surface roughness and corrosion stability in 3% NaCl was examined. At the same Ton/Toff ratio the current efficiency was insignificantly smaller for deposition at higher average current density. It was shown that, depending on the on-time, pulse plating could produce more homogenous alloy coatings with finer morphology, as compared to deposits obtained by direct current. The surface roughness was the greatest for Zn-Co alloy coatings deposited with direct current, as compared with alloy coatings deposited with pulse current, for both examined average current densities. It was also shown that Zn-Co alloy coatings deposited by pulse current could increase the corrosion stability of Zn-Co alloy coatings on steel. Namely, alloy coatings deposited with pulse current showed higher corrosion stability, as compared with alloy coatings deposited with direct current, for almost all examined cathodic times, Ton. Alloy coatings deposited at higher average current density showed greater corrosion stability as compared with coatings deposited by pulse current at smaller average current density. It was shown that deposits obtained with pulse current and cathodic time of 10 ms had the poorest corrosion stability, for both investigated average deposition current density. Among all investigated alloy coatings the highest corrosion stability was obtained for Zn-Co alloy coatings deposited with pulsed current at higher average current density (jav = 4 A dm-2).

Full Field Joule Heating Measurement of Copper Plate Using Phase Shifting Moire´ Interferometry in Microscopic Scale

2009 ◽  
Author(s):  
Bicheng Chen ◽  
Cemal Basaran
Keyword(s):  
Joule Heating ◽  
Current Density ◽  
Moiré Interferometry ◽  
Phase Shifting ◽  
Moire Interferometry ◽  
Heating Effect ◽  
Full Field ◽  
Microscopic Scale ◽  
Joule Heating Effect ◽  
Heating Effects

Heat generated from Joule heating is an important factor in several failure mechanisms in microelectronic packaging (e.g. thermomigration, electromigration and etc) and large amount of the heat causes severe heat dissipation problem. It is further exaggerated by the continuous marching towards miniaturization of microelectronics. The techniques of measuring the Joule heating effects at the microscopic scale are quite limited especially for the full field measurement. Infrared microscopic imaging has been reported to measure the heat radiation by the Joule heating in the microscopic scale. Moire´ interferometry with phase shifting is a highly sensitive and a high resolution method to measure the in-plane full field strain. In this paper, it is demonstrated that the Joule heating effect can be measured by Moire´ interferometry with phase shifting at the microscopic scale. The copper sheet is used for the demonstration because of isotropic material property and well known thermal properties and parameters. The specimen was designed to minimize the out-of-plane strain and the strain caused by the thermal-structural effects. A finite element model was developed to verify the design of the structure of the specimen and the specimen was tested under different current density (input current from 0 to 24 A). Based on the research, a correlation relationship between the current density and the strain in two orthogonal directions (one in the direction of the current flow) was determined. The regression coefficients of the full field were analyzed. The experiment demonstrates the capability of measuring microscopic Joule heating effects by using Moire´ interferometry with phase shifting. The method can be further applied to the measurement of Joule heating effect in the microscopic solid structures in the electronic packaging devices.

scholarly journals Electric Currents Connected With the Proton Flares of 7 July and 2 September, 1966

1971 ◽  
Vol 43 ◽  
pp. 417-421
Author(s):  
A. B. Severny
Keyword(s):  
Active Region ◽  
Field Strength ◽  
Magnetic Flux ◽  
Electric Field ◽  
Electric Field Strength ◽  
Electric Conductivity ◽  
Electric Current ◽  
Current Density ◽  
High Energy ◽  
Electric Currents

It is observed that the change of the net magnetic flux associated with flares can exceed 1017 Mx/s, which corresponds according to Maxwell's equation to the e.m.f. ∼ 109 V which is specific for the high energy protons generated in flares. It is shown that this value of e.m.f. can hardly be compensated by e.m.f. of inductance which should appear due to the actually measured motions in a flare generating active region. The values of electric field strength thus found, together with measured values of electric current density (from rotH), leads to an electric conductivity which is 103 times smaller than usually adopted.

Electrically-Assisted Forming of Magnesium AZ31: Effect of Current Magnitude and Deformation Rate on Forgeability

2012 ◽  
Vol 134 (3) ◽  
Author(s):  
Joshua J. Jones ◽  
Laine Mears ◽  
John T. Roth
Keyword(s):  
Current Density ◽  
Deformation Rate ◽  
Potential Benefit ◽  
Tensile Deformation ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Compressive Behavior ◽  
Electrically Assisted ◽  
Magnesium Az31 ◽  
First Time

Currently, the automotive and aircraft industries are considering increasing the use of magnesium within their products due to its favorable strength-to-weight characteristics. However, the implementation of this material is limited as a result of its formability. Partially addressing this issue, previous research has shown that electrically-assisted forming (EAF) improves the tensile formability of magnesium sheet metal. While these results are highly beneficial toward fabricating the skin of the vehicle, a technique for allowing the use of magnesium alloys in the production of the structural/mechanical components is also desirable. Given the influence that EAF has already exhibited on tensile deformation, the research herein focuses on incorporating this technique within compressive operations. The potential benefit of using EAF on compressive processes has been demonstrated in related research where other materials, such as titanium and aluminum, have shown improved compressive behavior. Therefore, this research endeavors to amalgamate these findings to Mg AZ31B-O, which is traditionally hard to forge. As such, to demonstrate the effects of EAF on this alloy, two series of tests were performed. First, the sensitivity of the alloy to the EAF process was determined by varying the current density and platen speed during an upsetting process (flat dies). Then, the ability to utilize impression (shaped) dies was examined. Through this study, it was shown for the first time that the EAF process increases the forgeability of this magnesium alloy through improvements such as decreased machine force requirements and increased achievable deformation. Additionally, the ability to form the desired final specimen geometry was achieved. Furthermore, this work also showed that this alloy is sensitive to any deformation rate changes when utilizing the EAF process. Last, a threshold current density was noted for this material where significant forgeability improvements could be realized once exceeded.

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