Introduction to Electrically Assisted Forming - Electrically Assisted Forming - page 25

The problem of decreased elongation in EAF-tensile processes was overcome in
2008, when Roth et al. [ 16 ] achieved elongation increases of nearly 400 % by apply-
ing square wave pulsed (rather than continuous) current to Al 5754 tensile speci-
mens. Following this, Salandro et al. [ 17 ] examined the effect of pulsed electricity
on three different heat treatments of two 5xxx Aluminum Alloys (5052 and 5083).
Moreover, in 2009, Salandro et al. [ 18 ] discovered a linear relationship between
current density and pulse duration in Mg AZ31B-O tensile specimens that could
be used to reliably achieve intended elongations for a variety of pulsing conditions.
Research by McNeal et al. [ 19 ] examined microstructural alterations in the same
Mg AZ31B-O tensile specimens. Green et al. [ 20 ] determined that springback in Al
6111 sheet specimens could be completely eliminated with a single high-current,
short-duration electrical pulse. From work by Jones and Roth [ 21 ], achievable com-
pressive displacements of the same Mg alloy were increased by over 400 %, and the
electricity even led to strain weakening effects. Additionally, in 2009, Salandro and
Roth [ 22 ] found that, by applying electric pulses to Al 5052 while undergoing highly
localized channel formation, the achievable channel depth could be increased while
reducing the required machine forces. Siopis et al. [ 23 ] examined how different
microstructure properties affect the effectiveness of EAF in micro-extrusion experi-
ments. Specifically, it was concluded that a finer-grained material, with more grain
boundaries, enhanced the electroplastic effect, whereas a larger-grained material,
with fewer grain boundaries, lessened the effect. Another work by Siopis et al. [ 24 ]
determined that the effectiveness of EAF increased as the dislocation density within
the metal also increased, as a result of cold-working prior to EAF experiments. A
work by Dzialo et al. [ 25 ] examined the effect of current density and zinc content
during electrical-assisted forming of copper alloys. A more in-depth overview of the
development of EAF can be found in [ 26 ]. Additionally, several recent EAF patents
were found as a part of the EAF literature review [ 27 - 31 ].
Overall, the effort and number of researchers studying EAF in the USA have
increased tremendously since Roth began experimentally analyzing EAF in the
mid-2000s. Shown in Fig. 2.3 is a timeline displaying both the researchers and
universities that are involved in some type of EAF research (note the exponentially
increasing trend).
2.2.1 EAF Theory and Modeling
Due to the lack of knowledge about the electroplastic effect, past research-
ers have been unsuccessful in accurately modeling and predicting EAF effects
for process control. However, from the previous work in this field, a multi-part
postulated theory can be explained. At the microstructure level, metals are held
together by metallic bonds, consisting of clouds of electrons, which surround ion
cores containing protons and neutrons. Because of this, it is realistic that the appli-
cation of electricity (i.e., the application of flowing electrons) to any metal will
have noticeable effects. Specifically, when electricity is applied to a metal during