Download explosive welding of magnesium alloy with aluminum and stainless

World Journal Of Engineering
EXPLOSIVE WELDING OF MAGNESIUM ALLOY WITH ALUMINUM AND
STAINLESS STEEL
Palavesamuthu Manikandan﹡, Joonoh Lee﹡, Akihisa Mori﹡﹡ and
Kazuyuki Hokamoto﹡﹡﹡
﹡
Graduate School of Science and Technology, Kumamoto University, 2-39-1 Kurokami,
Kumamoto 860-8555, Japan
﹡﹡
Shock Wave and Condensed Matter Research Center, Kumamoto University, 2-39-1 Kurokami,
Kumamoto 860-8555, Japan
﹡﹡﹡
Department of Mechanical Engineering, Sojo University, 4-22-1 Ikeda,
Kumamoto 860-0082, Japan
for all the experiments. The explosive SEP (density
and detonation velocity, 1310 kg/m3 and 6970 m/s
respectively), provided by Kayaku Japan
Corporation, Japan, was used for the experiments.
The thickness of the explosive was 5 mm. The
experimental setup and the different parameters
affecting the process have been described elsewhere
[3]. In this work, parameters such as thickness of
flyer plate, distance between the explosive and the
center of the sample, D, and the initial angle of the
experimental setup was varied to attain an optimum
microstructure for the welded combinations.
Microstructural characterization was done by
optical microscope, scanning electron microscope
and electron probe micro analyzer.
Introduction
There is a growing trend in automotive industry to
substitute light weight materials such as aluminum
and magnesium in an effort to improve fuel
economy and reduce emissions. Magnesium alloys
are gaining attention due to its low density and
good mechanical properties [1]. By combining
magnesium with another light metal aluminum or
with stainless steel, the cost can be effectively
decreased with good mechanical properties. For
practical applications, a good bonding strength of
the clad is required. Conventional joining
techniques are not suitable for the joining of
magnesium with other metals due to the difference
in the properties and the formation of brittle
intermetallic compounds. Explosive welding is an
alternate approach for the joining of dissimilar
materials [2]. Underwater explosive welding is a
variation by which any difficult to join materials
can be joined [3]. In this work, underwater
explosive welding technique was used to join
magnesium alloy with aluminum alloy and stainless
steel. The microstructural variations and the
conditions for obtaining a good welding are
reported.
Results and Discussion
Fig.1 shows the cross sectional optical micrograph
of the explosion welded A5052/AZ31. The
transition is seen as a clear wavy interface between
the participant metals associated with the vortices.
In explosive welding, when the collision parameters
are in the required range, a wavy interface is formed.
When the collision velocity is high, vortices are
formed. These vortices contain the intermetallic
compounds of magnesium and aluminum as this
combination is a metallurgically incompatible one.
The presence of these intermetallic compounds is
undesirable as it may degrade the bonding strength
of the clad. Hence, it is necessary to vary the
welding conditions so that a minimum or nil
intermetallics are formed. In underwater explosive
welding, the conditions can be changed by varying
the initial angle and the distance between the
explosive and the center of the sample. Fig. 2 shows
the microstructure of the explosive welded
A5052/AZ31 for the increased distance, D. When
the distance is increased, the shock pressure on the
sample is less. This reduced energy causes less
Experimental
Underwater explosive welding was employed for
the experiments. For all combinations, magnesium
alloy AZ31 was used as base plate. Aluminum alloy
A5052 and stainless steel SUS 304 was used as
flyer plate. The length and width of the welded
plates were 70 mm x 50 mm. The thickness of the
base plate was fixed as 3 mm, whereas the
thickness of the flyer plate was varied as 0.5 mm
and 1 mm. A 0.2 mm thick stainless steel was used
as a cover plate for Al/Mg combination only. The
stand off distance between the plates was 0.2 mm
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World Journal Of Engineering
plastic deformation along the interface which in
turn favors the formation of small waves with small
or nil vortices. By reducing the vortices, it is
expected that the bonding strength is high for this
clad.
SUS 304
A5052
AZ 31
100 mm
Fig.3 Welded interface of 0.5 mm stainless steel/AZ31
for D=25 mm,  = 30°
AZ 31
SUS 304
100 mm
Fig.1 Welded interface of 0.5 mm A5052/AZ 31 for
D=25 mm,  =30°
A5052
AZ 31
100 mm
Fig.4 Welded interface of 0.5 mm stainless steel/AZ31
for D=60 mm,  = 30°
Conclusion
AZ 31
100 mm
Underwater explosive welding was used to clad
magnesium alloy with aluminum alloy and stainless
steel. A wavy interface with vortices was formed for
A5052/AZ31. The vortices containing intermetallic
compounds were reduced by changing the welding
conditions. In case of SUS304/AZ31, a flat
interface with a thin resolidified interlayer was
formed. The welding conditions were changed to
obtain an interlayer free interface.
Fig.2 Welded interface of 0.5 mm A5052/AZ 31 for
D=60 mm,  =30°
Fig.3 shows the microstructure of magnesium alloy/
0.5 mm stainless steel. The welded interface
exhibits a flat interface between the participant
metals. In general, the explosive welded interface
exhibits a wavy structure. However, in cases, when
the participant metals have a vast difference in the
properties, a flat interface is formed similar to the
ones reported for metal/ceramic. Further, a thin
layer is formed along the interface. This is due to
the presence of a resolidified interlayer formed by
the difference in the melting points of the
participating components. Though magnesium and
stainless steel does not form any intermetallic
compounds, it is necessary to make an interlayer
free interface. Hence, the experiments were
conducted by changing the distance, D. Fig. 4
shows the microstructure of the AZ31/SUS304
when the distance is increased. The microstructure
reveals a clear flat interface with no resolidified
interlayer. It is also possible to make an interlayer
free interface by changing the initial angle.
Acknowledgements
The authors acknowledge the support of funding by
Global COE program on Pulsed Power Engineering,
Kumamoto University.
References
1. Chen, Y.C. and Nakata, K. Scripta Mater. 58
(2008) 433-436.
2. Crossland, B. “Explosive Welding of Metals and
Its Application”, Oxford Univ. Press, UK (1981).
3. Hokamoto, K., Nakata, K., Mori, A., Tsuda, S.,
Tsumura, T., and Inoue, A., J. Alloy Compd
472 (2009) 507-511.
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