FIELD OF THE INVENTION
The present investigation relates to a novel solid state method of producing a
sound weld between two mild steels plates. The invention further relates to a
green method of production of sound weld between two mild steels plates.
BACKGROUND OF THE INVENTION
Joining and welding is one of the important post-processing areas in every
industrial application; starting from construction, automotive sheep building,
etc. The most common method of welding is fusion welding. In fusion
welding process, a high temperature is generated near the plates which are
high enough to melt the jobs and it further solidifies and produces a sound
weld. Very often gas and flux shrouding are used to protect the pieces from
oxidation. Consumables like filler materials are often used as well. Because of
the high temperature and presence of gas and flux, this process is not a very
environmentally friendly process.
Apart from fusion welding, there are few solid state welding process are also
available, such as friction stir welding, explosive welding and magnetic pulse
welding.
Friction stir welding (FSW) is a solid-state joining process that uses a non-
consumable tool to join two facing workpieces without melting the workpiece
material. Heat is generated by friction between the rotating tool and the
workpiece material, which leads to a softened region near the FSW tool.
While the tool is traversed along the joint line, it mechanically intermixes the
two pieces of metal, and forges the hot and softened metal by the
mechanical pressure, which is applied by the tool, much like joining clay, or

dough [Welding process and its parameters - Fraction Stir Welding -
www.fswelding.com]. In general, FSW has been found to produce a low
concentration of defects and is very tolerant of variations in parameters and
materials.
Explosion welding (EXW) is a solid state (solid-phase) process where welding
is accomplished by accelerating one of the components at extremely high
velocity through the use of chemical explosives. This process is most
commonly utilized to clad carbon steel plate with a thin layer of corrosion
resistant material (e.g., stainless steel, nickel alloy, titanium, or zirconium).
Due to the nature of this process, producible geometries are very limited
[Lancaster, 1999].
Explosion welding can produce a bond between two metals that cannot
necessarily be welded by conventional means. The process does not melt
either metal, instead plasticizing the surfaces of both metals, causing them to
come into intimate contact sufficient to create a weld. This is a similar
principle to other non-fusion welding techniques, such as friction welding.
Large areas can be bonded extremely quickly and the weld itself is very
clean, due to the fact that the surface material of both metals is violently
expelled during the reaction.
A disadvantage of this method is that extensive knowledge of explosives is
needed before the procedure may be attempted safely. Regulations for the
use of high explosives may require special licensing.
Magnetic pulse welding (MPW) is another solid state welding process that
uses magnetic forces to weld two workpieces together. The welding
mechanism is most similar to that of explosion welding [Weman 2003].
Dissimilar metals can be welded, which cannot be joined by fusion welding.

With magnetic pulse welding high quality welds in similar and dissimilar
metals can be made in microseconds without the need for shielding gases or
welding consumables.
In MPW process, two components to be joined are called target and flyer.
The flyer is normally the alloy/metal of higher conductivity, such as Al or Cu
and the target can be similar or a different material. Many researchers have
reported good metallurgical joining of light weight high conductive metals
with similar metals or some other metals.
Ben-Artzy et al. (2008) used MPW process to weld Al-1050 and unalloyed Mg
and reported presence of intermetallic phases of different compositions at the
interface. Stern and Aizenshtein [Stern and Aizenshtein, 2002] joined Al -
1050 with Mg-AZ91 and indicated presence of semi-regular, wavy transition
layer made of intermetallic phases. In another study, Stern et al. (2013)
welded Al with Mg-AZ31 alloy by MPW process and demonstrated
heterogeneous nature of transition layer which contained both intermetallic
phase as well as super saturated solid solution. Other important dissimilar
metals combination joined by MPW method reported in literature are Al1050
– mild steel [Stern and Aizenshtein, 2002], Cu-brass [Faes et. al, 2010], Cu-
steel [Patra et al., 2017], Al – Stainless Steel [Kore et al, 2008], Al-Cu [Gobel
et al., 2010], etc. Like Al-Mg, Stern and Aizenshtein (2002) described
formation of a brittle intermetallic layer at the interface of steel and
aluminium too. Faes et al. (2010) investigated weldability of copper tubes to
brass solid work pieces and reported presence of melting and rapid
solidification at the weld interface. In their recent work, Patra et. al (2017)
obtained successful joint between an industrially produced steel tube with a
Cu tube and observed presence of nano-grains by transmission electron
microscopy. Kore et. al (2008) used an Al-driver sheet to accelerate their
stainless steel (SS) plate and joined SS with Al sheet. They used an ‘L’ shaped

flat one turn copper coil and identified presence of continuous weld. Gobel
et. al (2010) joined Al-flyer with Cu-cylinders by same electromagnetic
welding route and showed presence of wavy as well as wave-less interfacial
morphology. They also reported presence of melt pockets and intermetallic
formation at the interface. In case of dissimilar metals joining, liquefaction of
one or both material and presence of ultrafine grains due to very fast cooling
from liquid stage were frequently witnessed [Stern et. al, 2014].
Stern et. al, (2014) investigated MPW joining of similar metal combinations
such as Al 7075 to Al 7075, Cu-Cu and SS 40900 to SS 40900 and found grain
refinement at the interface region in all the three cases which they attributed
to melting and rapid solidification. Watanabe and Kumai (2009) performed
MPW of Al-Al and Cu-Cu lap joint and wavy interface morphology was
reported. Berlin et al. (2011) successfully performed MPW on Mg AZ31 alloys
sheets and observed presence of ultra-fine equiaxed as well as severely
elongated grains at and near the weld interface which they concluded due to
severe plastic deformation.
MPW process is quite popular in axis-symmetric set up, such as tube-tube
joining because of the easy control over the experimental parameters. In the
work of Marya and Marya (2004), tubes of Al and Cu were joined by MPW
process where Al being the lighter material used as the flyer. A collision angle
of 9° was formed to maintain a broad range of separation gap. Apart from
good wavy interface they also reported discontinuous presence of brittle
intermetallic phase embedded with micro-voids in the regions where collision
velocity was significantly higher. Marya et al (2005) also studied
electromagnetic joining of Al-SS and Al-Ti and interestingly concluded that
presence of intermetallic phase at the interface may not necessarily be
detrimental all the time and attributed the superior crack susceptibility of Al-

SS joint to the formation of thicker intermetallic phase. Apart from tube-tube,
Kimchi et al. (2004) successfully welded an Al 6061 tube with a 1010 steel
bar using a 90kJ MPW machine. On the other hand, Stern and Aizenshtein
(2002) joined Al 1050 tube with mild steel bar and ferritic stainless steel tube
with same grade steel bar by MPW process.
However, use of MPW process to join flat sheets is not extensively
documented. Nevertheless, few works have been reported in open literature.
Aizawa (2004) described seam welding of overlapping Al sheet with steel
sheet using this process. They observed an alloy layer of 10µm at the Al-Fe
interface. Okagawa and Aizawa (2004) joined two Al 1050 sheets of 1 mm
thickness by MPW process and concluded that the shearing strength of the
joint is probably depend on the kinetic energy of the sheets just before the
collision. Zhang et al. (2008a) showed presence of high degree of local
misorientation near the interface of the AA 6061-T6 sheets joined by MPW
and further concluded that the bonding was primarily solid state bonding.
Recently, Kore and his group [Kore et al., 2007; 2008; 2009a] demonstrated
the feasibility of joining flat sheets of Al-Al, Al-SS, Mg-Al and Al-Al-Li alloy by
this process. Kore et al. (2007) extensively studied the effect of MPW process
parameters such as stand-off distance, coil geometry, energy, etc. on the
quality and strength of two Al sheets of 1 mm thickness bonded by this
process. They concluded that there is an optimum value of stand-off distance
which gives maximum shearing strength. Kore et al. (2008) made similar kind
of observations when they successfully joined 1 mm Al sheet with 0.25 mm
stainless steel (SS) sheets using an aluminium plate as a driver for SS sheet.
In a similar fashion, the same group of researchers (Kore et al., 2009) could
effectively welded Al with Al-Li sheets of 1 mm thickness each; by using a 1
mm thick Al driver to drive electrically poor conductive Al-Si sheet.
Nonetheless, as opined by Kore et al. (2010), application of MPW process to

join two flat sheets is limited due to the difficulty in controlling the magnetic
field along the entire length of the coil.
Reports of joining two steel components by MPW process are rare. This is
mainly attributed to the lower conductivity of steel and its weight as
compared to the other popular metals such as Al or Cu. Stern and Aizenshtein
[Stern and Aizenshtein 2002] reported similar ferritic stainless steel joining by
MPW process in a tube-bar set up. They reported a very fine grained pocket
type structure at the interface with higher hardness. They also stated
presence of a small amount of austenite (Y-phase) which was attributed
towards the rapid nature of the cooling process. There has been practically
no information on the steel-steel joining by MPW process where both flyer
and target are sheets and/or plates.
Few researchers have reported steel-steel plate joining by explosive welding
(EXW) process, which as stated rightly by Verstraete et. al. (2011) is
considered to be the higher energy version of the MPW process. Kacar and
Acarer (2003) explosively cladded 2 mm thick duplex stainless steel (2205
grade) with vessel steel of 10 mm thickness, where the former was used as
the flyer plate. They reported wavy interface morphology with little
degradation of corrosion and mechanical properties. In another study, Kacar
and Acarer (2004) welded vessel steel with 316 stainless steel plates by the
same EXW process and reported wavy interface along with occasional
presence of local melting zones. In another instance, Zamani and Liaghat
(2012) joined 316 SS pipes with carbon steel pipes by the same process.
They observed that the transition from wavy interface to flat interface
depends on the explosive loading; lower explosive loading lead to flat
interface. Not only interface morphology changed by increasing explosive
loading but the amplitude and wavelength of the waves also increased. In
summary, simultaneous presence of wavy and flat interface with occasional

evidence of local melting at the weld zone was observed in plate-plate joining
of EXW. Increasing explosive loading was found to have a direct correlation
on the flat to wavy interfacial transformation.
In a very recent publication by Ghosh et al. (2018), two steel plates of
different compositions (one mild steel and one full hard IF steel) and different
thickness are joined by MPW process and the working window of the same
has been identified. The mild steel was of 0.5 mm thickness whereas the
IFFH was of 1 mm thickness. The yield strength of the mild steel and the
IFFH plate was 203 and 616 MPa, respectively. A very narrow window of 16
kV working voltage and 0.8 mm stand-off distance was found for a sound
weld.
It has been a well-established fact that in MPW process, the parameters
changes appreciably once the materials and dimensions changes, especially
materials and for each set different working window needs to be established
in order to get a sound weld.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a working
window for joining two mild steel plates of similar composition and similar
strength by magnetic pulse welding.
Another object of the present invention is to propose a working window for
joining two mild steel plates of similar composition and similar strength with a
green process.

Another object of the present invention is to propose a method of joining two
mild steel plates of similar composition and similar strength without formation
of a heat affected zone.
SUMMARY OF THE INVENTION
The investigation discloses a methodology of joining two mild steel plates of
magnetic pulse welding process. Two thin (<0.5 mm) mild steel plates with
nominal compositions of C <0.06, Mn< 0.5, S< 0.01, P < 0.01, Si< 0.02 and
Al<0.05 wt. % are joined by magnetic pulse welding process. A flat one turn
coil with 2 mm overlapping width is used for this experiment. In order to
overcome the low conductivity of steel plate, an aluminium sheet of 0.5 mm
thickness is used as the driver plate. Stand-off distance is varied between 0.5
mm to 1.5 mm by adjusting the target side bottom fixture. Discharge voltage
is also varied; the lowest discharge voltage is used as 12 kV whereas the
highest was 16 kV. The plates were kept parallel to each other with an initial
collision angle of 0°. A sound weld is established between working distance of
0.8 to 1.3 mm and a working voltage of 13.5 to 14.5 volt.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1: MPW welded mild steel plates showing presence of sound weld
macroscopically as well as microscopically.
Figure 2: MPW welded mild steel plates showing presence of sound weld and
proper diffusion bonding even at higher magnifications.

DETAILED DESCRIPTION OF THE INVENTION
The MPW equipment is rated at 25 kV discharge voltage and 50 kJ discharge
energy with total capacitance of 160µF. A flat one turn coil made up of
precipitation hardened Cu-Cr-Zr alloy with 2 mm overlapping width is used for
this experiment. The thicknesses of the plates are 0.5 mm. In order to
overcome the low conductivity of steel plate, an aluminium sheet of 0.5 mm
thickness is used as the driver plate. The conductivity of the Al sheet was 2.8
X 107 Siemens/m. The surfaces of the plates are cleaned with alcohol before
testing. There is an overlapping width of 10 mm between the top target plate
and the bottom flyer plate. Stand-off distance was varied between 0.5 mm to
1.5 mm by adjusting the target side bottom fixture. The top fixture is finally
clamped with the bottom one to give the rigidity to the whole set up.
Discharge voltage is also varied; the lowest discharge voltage is used as 12
kV whereas the highest is 16 kV. The plates are kept parallel to each other
with an initial collision angle of 0°.
Different working distances such as 0.5, 0.8, 1, 1.3, 1.5 mm are used with
varying voltage such as 12, 12.5, 13, 13.5 and 14, 15 and 16. For 0.5 mm
standoff distance (SD) no weld could be established in any voltage. No weld
could be established in any voltage below 13.5 kV. Again now weld could be
achieved for SD 1.5 and above. Sound weld can only obtained for SD 0.8 to
1.3 and voltage above 13.5kV. However, Voltage beyond 14.5 kV shows poor
weld morphology with lot of porosity.
Example:
Two mild steel plates of 0.5 mm thickness were joined by magnetic pulse
welding process. The chemical composition and the mechanical properties are
given in Table 1 and 2 respectively. A standoff distance of 1.3 mm and
voltage of 13.5 were maintained. A flat one turn coil made up of precipitation

hardened Cu-Cr-Zr alloy with 2 mm overlapping width was used for this
experiment. The flyer (bottom) and the target (top) plates were 200 mm long
and 70 mm wide. The driver aluminium sheet of 0.5 mm thickness was used
as the driver plate. The conductivity of the Al sheet was 2.8 X 107
Siemens/m. The surfaces of the plates were cleaned with alcohol before
testing. There was an overlapping width of 10 mm between the top target
plate and the bottom flyer plate.
Figure 1 shows welded plates and corresponding microstructure showing
sound weld between two plates. Almost 1 mm wide welded joint was
established in this case. Figure 2 shows scanning electron microstructures of
the welded plates. The interface clearly shows diffusion bonding without
presence of any pores or holes. From this figure it is clearly seen that there is
no evidence of Heat Affected Zone (HAZ) or grain growth near the weld line.
So this process is capable of producing a sound weld without formation of
any HAZ.
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WE CLAIM :
1. A method of joining two mild steel plates of similar composition and
similar strength without formation of a heat affected zone, by Magnetic
Pulse Welding Process on an MPW (Magnetic Pulse Welding) machine,
the method comprising:
placing the two similar steel plates at the MPW machine;
setting a stand-off distance between the steel plates at 0.8 to
1.5 (mm);
setting a Working voltage (kV) between 12.5 to 16.0 KV;
setting an overlapping length and width of 1 - 10 mm; wherein:
the composition of the steel plates being Steels C:0.02 to 0.05,
Mn: 0.1 - 0.5, S<0.01, P<0.02, Si<0.2, Al:0.02 - 0.05 and
YS:150 – 300 MPa, UTS:250 – 400 MPa and %El >10%, and
wherein the steel plates are kept parallel to each other within
an initial collision angle of 00.
2. The method as claimed in claim 1, wherein the thickness of the steel
plates is 0.5 mm and below.