R. KOSTUREK et al.: RESEARCH ON THE MICROSTRUCTURE OF A Ti6Al4V-AA1050 EXPLOSIVE-WELDED ...
109–113
RESEARCH ON THE MICROSTRUCTURE OF A Ti6Al4V-AA1050
EXPLOSIVE-WELDED BIMETALLIC JOINT
RAZISKAVA MIKROSTRUKTUR EKSPLOZIVNO VARJENIH
BIMETALNIH SPOJEV Ti6Al4V-AA1050
Robert Kosturek
1
, Marcin Wachowski
1
, Lucjan Œnie¿ek
1
, Adam Kruk
2
, Janusz Torzewski
1
,
Krzysztof Grzelak
1
, Janusz Mierzyñski
1
1
Military University of Technology, Faculty of Mechanical Engineering, 2 Generala Witolda Urbanowicza Street, Warsaw, Poland
2
Department of Physical and Powder Metallurgy, Faculty of Metal Engineering and Industrial Computer Science, AGH University of Science
and Technology, al. A. Mickiewicza 30, Krakow, Poland
Prejem rokopisa – received: 2018-07-15; sprejem za objavo – accepted for publication: 2018-10-17
doi:10.17222/mit.2018.153
Some of the most interesting materials with superior ballistic resistance are light-alloy laminated composite plates. The
appropriate technology to produce these composites is the explosive-welding method. In this study, Ti6Al4V and AA1050 were
successfully bonded during an explosive-welding process. The microstructure of the obtained bimetal joint was examined with
scanning electron microscopy on the samples prepared using the ion-polishing method. Scanning electron microscopy allowed
us to investigate the grain size in the joint area and the presence of the melted zones in the joint area, formed as a result of local
mixing of both joined materials. In order to investigate the melted zones in terms of the presence of intermetallic compounds,
linescans and transmission-electron-microscopy observations with SAED were performed. The obtained results allowed us to
identify the intermetallic compounds, which occurred in the melted zones. The scanning-electron-microscope observations
indicated a severe plastic deformation of both materials in the joint zone. An analysis of the microstructure of the joint zone
with a particular emphasis on the melted zones was performed together with the tomography carried out with the
focused-ion-beam scanning-electron-microscope method (FIB/SEM). The strain hardening of the joined materials was
established with a microhardness analysis.
Keywords: explosive welding, Ti6Al4V, microstructure, intermetallic compounds
Nekaj najbolj zanimivih materialov z odli~nimi protibalisti~nimi lastnostmi je izdelanih iz laminatnih kompozitnih plo{~ na
osnovi lahkih zlitin. Primerna tehnologija za njihovo izdelavo je metoda eksplozivnega varjenja. V tej {tudiji so avtorji s
postopkom eksplozijskega varjenja med seboj uspe{no spojili zlitini Ti6Al4V in AA1050. Mikrostrukturo ionsko poliranih
vzorcev izdelanih bimetalnih spojev so opazovali pod vrsti~nim elektronskim mikroskopom (SEM). Opazovanje pod SEM je
omogo~alo dolo~itev velikosti kristalnih zrn na mestu spoja in prisotnost pretaljenih podro~ij, ki so nastala kot rezultat
lokalnega me{anja obeh materialov. S pomo~jo linijskega skeniranja na presevnem elektronskem mikroskopu (TEM/SAED) so
raziskovali pretaljena podro~ja glede na nastanek intermetalnih spojin. Dobljeni rezultati so omogo~ili identifikacijo
intermetalnih spojin, ki so nastale v pretaljenih podro~jih spoja. SEM posnetki ka`ejo, da je med eksplozijskim varjenjem pri{lo
do mo~ne plasti~ne deformacije obeh materialov na mestu spajanja. Analizo mikrostrukture v podro~ju spoja s poudarkom na
pretaljena podro~ja so izvedli tudi s tomografijo na FIB/SEM. Z meritvami mikrotrdote na bimetalnem spoju so potrdili
deformacijsko utrjevanje eksplozijsko varjenih materialov.
Klju~ne besede: eksplozivno varjenje, Ti6Al4V, mikrostruktura, intermetalne spojine
1 INTRODUCTION
Light-alloy laminated composites are some of the
most promising materials for military applications due to
their combination of low density and ballistic resist-
ance.
1–4
Some of the most interesting laminates in terms
of the application for ballistic panels are Al-Ti alloy
systems.
5–9
The appropriate technology for obtaining
such laminated metal composites (LMC) is the explo-
sive-welding method, a solid-state welding process, in
which the metallic bond between the elements is formed
due to a high velocity collision caused by the detonation
of the explosive material.
10–14
As the result of a severe
plastic deformation during bonding, as well as local
mixing of the joined materials, melted zones (vortexes)
can be formed.
14,15–17
These areas often contain joint
defects such as voids and cracks, and for this reason,
their presence in the joint interface is highly undesirable.
Additionally, in the case of Al-Ti, explosive-welded
laminated intermetallic compounds with a Ti-Al phase
may occur in the melted zones.
14,18–21
2 EXPERIMENTAL PART
The aim of this research was to study the microstruc-
ture of explosive-welded sheets of titanium alloy
Ti6Al4V and aluminum alloy AA1050 with a particular
emphasis on the melted zones. The chemical composi-
tion of the welded plates is presented in Table 1.Asthe
explosive material, a mixture of ammonium-nitrate fuel
oil (ANFO) was used. The scheme of the explosive-
welding system is presented in Figure 1. Metallographic
Materiali in tehnologije / Materials and technology 53 (2019) 1, 109–113 109
UDK 620.1:669.018:669.71’295:621.791 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 53(1)109(2019)
*Corresponding author e-mail:
robert.kosturek@wat.edu.pl

observations were carried out using samples cut from the
welded sheet in the direction perpendicular to the
welding direction. The microstructure of the specimens
was investigated with a ZEISS scanning electron
microscope equipped with energy-dispersive x-ray spec-
troscopy (EDS) and a back-scattered electron (BSE)
detector. EDS was used to perform the mapping
measurements of the chemical-composition distribution
throughout the cross-sections of the samples. Obser-
vations were carried out along the cross-sections of the
samples using acceleration voltages in a range of
10–16 kV. Linescans were performed at an acceleration
voltage of 15 kV. Before the structural examinations, all
the samples were subjected to a metallographic pre-
paration involving ion polishing. In order to present the
distribution of intermetallic precipitates in the melted
zone, tomography was performed using the focused-ion-
beam scanning-electron-microscope method (FIB/SEM).
Additionally, the obtained joint was subjected to a
microhardness analysis with a load of 100 g and the
established microhardness distribution allowed us to
estimate the strain hardening of the materials joined in
the explosive-welding process.
3 RESULTS
The scanning electron microscopy performed on the
Ti6Al4V–AA1050 explosive-welded joints revealed a
flat-shaped geometry of the obtained bond. No imperfec-
tions such as cracks or voids were noticed, which
indicates a defect-free structure of the joint interface.
Between the joined materials, a continuous melted zone
occurs with a width of about 5–10 μm. The photos of the
joint are presented in Figure 2a.
The average grain size in the joint zone is 2.3±0.8 μm
for AA1050 and 3.2±0.3 μm for Ti6Al4V (Figure 2b).
Directly on the joint line, there is a 4.5-μm wide region
of Ti6Al4V fragmented grains with a size of 1.4±0.3 μm
(Figure 3).
The analysis of the distribution of the main alloying
elements in the joint area – titanium (Figure 4a) and
aluminum (Figure 4b) – indicates that the melted zone
contains a mixture of both joined materials with a
predominance of aluminum. Titanium is concentrated in
the precipitates occurring in the melted zone, which were
subjected to further investigations.
R. KOSTUREK et al.: RESEARCH ON THE MICROSTRUCTURE OF A Ti6Al4V-AA1050 EXPLOSIVE-WELDED ...
110 Materiali in tehnologije / Materials and technology 53 (2019) 1, 109–113
Table 1: Chemical composition of the welded plates
Fe (%) Si (%) Zn (%) Mg (%) Ti (%) Mn (%) Cu (%) Al (%)
AA1050
0.4 0.25< 0.07< 0.18 0.05< 0.05< 0.05< balance
O (%) V (%) Al (%) Fe (%) H (%) C (%) N (%) Ti (%)
Ti6Al4V <0.20 3.5 5.5 <0.30 <0.0015 <0.08 0.05< balance
Figure 2: Scanning-electron-microscopy images of the joint interface
Figure 1: Scheme of the explosive-welding system
Figure 3: Scanning-electron-microscopy image of the Ti6Al4V
microstructure of the joint zone

The precipitates are localized in the melted zone as
an almost uniform dispersion with the average size of
0.18 μm. It was noticed that a fine dispersion of the
precipitates occurs near the Ti6Al4V alloy layer. On the
R. KOSTUREK et al.: RESEARCH ON THE MICROSTRUCTURE OF A Ti6Al4V-AA1050 EXPLOSIVE-WELDED ...
Materiali in tehnologije / Materials and technology 53 (2019) 1, 109–113 111
Figure 7: Transmission electron microscopy of the melted zone and the SAED analysis results for the marked area compared to the Ti-Al
intermetallic patterns
Figure 5: Scanning-electron-microscopy image of the precipitates in
the melted zone
Figure 6: Linescan-analysis results for the melted zone
Figure 4: Distribution of alloying elements on the surface of a sample
from the joint area: a) titanium and b) aluminum

other hand, larger precipitates were found in the middle
of the melted zone (Figure 5).
The results of the linescan analysis confirmed the
fluctuations in the concentrion of the alloying elements
in the melted zone, indicating differences between the
distributions of titanium and aluminum in the precipi-
tates and the surrounding melted zone (Figure 6).
Transmission electron microscopy (Figure 7a) and
selected area diffraction (SAED) were performed in
order to investigate the precipitates in the melted zone
(Figure 7b). The obtained pattern was compared to the
patterns of the Ti-Al intermetallic compounds. As a
result, three intermetallic compounds were found in the
melted zone: TiAl
3
(Figure 7c), TiAl (Figure 7d) and
TiAl
2
(Figure 7e).
In order to present the distribution of the intermetallic
precipitates in the melted zone, the FIB-SEM tomogra-
phy was performed (Figure 8a) together with a 3D
visualization (Figure 8b and 8c).
The results of the microhardness analysis indicate a
slight increase in the microhardness of the jointed mate-
rials due to explosive welding carried out at a distance of
100 μm from the joint line (Figure 9). The measured
microhardness of the base materials before the welding
process was 350±12 HV0.1 in the case of Ti6Al4V and
40±5 HV0.1 in the case of AA1050. Compared to the
base-material microhardness, the microhardness of
AA1050 and Ti6Al4V was higher by about 15 HV0.1
and 40 HV0.1, respectively.
4 DISCUSSION
The explosive-welding technology allowed us to
produce a defect-free joint between the Ti6Al4V and
AA1050 alloys. The joined materials were subjected to a
severe plastic deformation during the welding process
that resulted in a fragmentation of the grains in the joint
zone. The average grain size of AA1050 in the joint zone
was established as 2.3±0.8 μm. At the same time, the
difference in the grain size of Ti6Al4V allowed us to
specify two regions: the first one occurred at a distance
of up to 4.5 μm from the joint line, with the average
grain size of 1.4±0.3 μm, and the other region exhibited
the average grain size of 3.2±0.3 μm. The presence of a
continuous melted zone in the joint with the average
width of 5–10 μm was reported. The result of the distri-
bution of alloying elements on the surface of a sample
indicates that the melted zone was formed during explo-
sive welding due to the mixing of both joined materials
with a predominance of the AA1050 alloy. The concen-
tration of aluminum in the melted zone is uniform, in
contrast to titanium, which is concentrated in the precipi-
tates occurring in this area. For the precipitates dis-
tributed in the melted zone, the average size of 0.18 μm
was reported. The results of FIB-SEM tomography
allowed us to perform a 3D visualization of the preci-
pitates in the analyzed melted zone. Selected area
diffraction (SAED) indicates a presence of three inter-
metallic types: TiAl
3
, TiAl, and TiAl
2
. The formation of
intermetallic compounds in the melted zone was caused
by local melting and mixing of the joined materials dur-
ing the explosive-welding process. Plastic deformation
of the welded plates caused their strain hardening, which
was investigated with a microhardness analysis. The
microhardness of the joined materials slightly increased
at a distance of 100 μm from the joint line.
5 CONCLUSIONS
Explosive welding of AA1050 and Ti6Al4V results
in a formation of the joined materials and a fragmenta-
tion of the grain structure. The continuous melted zone
occurring in the joint exhibits a fine dispersion of
intermetallic precipitates. An analysis of the precipitates
allowed us to identify the types of intermetallic com-
pounds as TiAl
3
, TiAl, and TiAl
2
.
Acknowledgment
This work used the results of the research made
within a project co-financed by the Polish Ministry of
National Defense, no. PBG/13-998. This work was also
R. KOSTUREK et al.: RESEARCH ON THE MICROSTRUCTURE OF A Ti6Al4V-AA1050 EXPLOSIVE-WELDED ...
112 Materiali in tehnologije / Materials and technology 53 (2019) 1, 109–113
Figure 9: Results of the microhardness analysis
Figure 8: FIB-SEM tomography together with a 3D visualization of
the precipitates

supported by Project PBS2/A5/35/2013 funded by the
National Research and Development Centre.
6 REFERENCES
1
I. Crouch, The Science of Armour Materials, Woodhead Publishing
2016
2
H. Gower, D. S. Cronin, A. Plumtree, Ballistic impact response of
laminated composite panels, Inter. J. of Imp. Eng., 35 (2008),
1000–1008, doi:10.1016/j.ijimpeng.2007.07.007
3
M. Übeyli, Y. Orhan, B. Ögel, On the comparison of the ballistic per-
formance of steel and laminated composite armors, Mat. and Des.,
28 (2007), 1257–1262, doi:10.1016/j.matdes.2005.12.005
4
S. M. R. Khalili, R. A. Mittal, K. S. Gharibi, A study of the me-
chanical properties of steel/aluminium/GRP laminates, Mat. Sc. and
Eng. A, 412 (2005), 137–140, doi:10.1016/j.msea.2005.08.016
5
N. Thiyaneshwaran, K. Sivaprasad, B. Ravisankar, Work hardening
behavior of Ti/Al-based metal intermetallic laminates, The Int. J. of
Adv. Man. Tech., 93 (2017), 361–374, doi:10.1007/s00170-016-
9382-x
6
D. Peru{ko, S. Petrovi}, M. Stojanovi}, M. Mitri}, M. ^izmovi}, M.
Panjan, M. Milosavljevi}, Formation of intermetallics by ion implan-
tation of multilatered Al/Ti nano-structures, Nuc. Instr. and Meth. in
Ph. Research Section B., 282 (2012), 4–7, doi:10.1016/j.nimb.
2011.08.038
7
L. M. Peng, J. H. Wang, H. Li, J. H. Zhao, L. H. He, Synthesis and
microstructural characterization of Ti–Al3Ti metal–intermetallic
laminate (MIL) composites, Scr. Mat., 52 (2005), 243–248,
doi:10.1016/j.scriptamat.2004.09.010
8
M. Ma, P. Huo, W. C. Liu, G. J. Wang, D. M. Wang, Microstructure
and mechanical properties of Al/Ti/Al laminated composites
prepared by roll bonding, Mat. Sc. and Eng.: A, 636 (2015),
301–310, doi:10.1016/j.msea.2015.03.086
9
H. Yu, C. Lu, K. Tieu, H. Li, A. Godbole, X. Liu, C. Kong, Enhanced
materials performance of Al/Ti/Al laminate sheets subjected to
cryogenic roll bonding, J. of Mat. Res., 32 (2017), 3761–3768,
doi:10.1557/jmr.2017.355
10
T. Z. Blazynski, Explosive Welding, Forming and Compaction,
Applied Science, 1983, doi:10.1007/978-94-011-9751-9
11
F. Findik, Recent developments in explosive welding, Mat. and Des.,
32 (2011), 1081–1093, doi:10.1016/j.matdes.2010.10.017
12
R. Kosturek, M. Najwer, P. Nieslony, M. Wachowski, Effect of heat
treatment on mechanical properties of Inconel 625/steel P355NH
bimetal clad plate manufactured by explosive welding, Adv. in Man.,
(2018), 681–686, doi:10.1007/978-3-319-68619-6_65
13
D. M. Fronczek, R. Chulist, Z. Szulc, J. Wojewoda-Budka, Growth
kinetics of TiAl3 phase in annealed Al/Ti/Al explosively welded
clads, Mat. Let., 198 (2017), 160–163, doi:10.1016/j.matlet.2017.
04.025
14
D. M. Fronczek, R. Chulist, L. Litynska-Dobrzynska, G. A. Lopez,
A. Wierzbicka-Miernik, N. Schell, Z. Szulc, J. Wojewoda-Budka,
Microstructural and phase composition differences across the
interfaces in Al/Ti/Al explosively welded clads, Metall. and Mat.
Trans. A, 48 (2017), 4154–4165, doi:10.1007/s11661-017-4169-8
15
G. H. S. F. L. Carvalho, I. Galvão, R. Mendes, R. Leal, A. Loureiro,
Formation of intermetallic structures at the interface of
steel-to-aluminium explosive welds. Mat. Ch., 142 (2018), 432–442,
doi:10.1016/j.matchar.2018.06.005
16
H. Paul, M. M. Miszczyk, R. Chulist, M. Pra¿mowski, M. Mariusz, J.
Morgiel, A. Ga³ka, M. Faryna, F. Brisset, Microstructure and phase
constitution in the bonding zone of explosively welded tantalum and
stainless steel sheets, Mat. & Des.,153 (2018), 177–189,
doi:10.1016/j.matdes.2018.05.014
17
A. Loureiro, R. Mendes, J. B. Ribeiro, R. Leal, I. Galvão, Effect of
explosive mixture on quality of explosive welds of copper to
aluminium, Mat. & Des., 95 (2016), 256–267, doi:10.1016/
j.matdes.2016.01.116
18
M. Mirjalili, M. Soltanieh, K. Matsuura, M. Ohno, On the kinetics of
TiAl3 intermetallic layer formation in the titanium and aluminum
diffusion couple, Intermet., 32 (2013), 297–302, doi:10.1016/
j.intermet.2012.08.017
19
D. Peru{ko, S. Petrovi}, J. Kova~, Z. Stojanovi}, M. Panjan, M.
Obradovi}, M. Milosavljevi}, Laser-induced formation of inter-
metallics in multilayered Al/Ti nano-structures, J. of Mat. Sci., 47
(2012), 4488–4495, doi:10.1007/s10853-012-6311-8
20
B. Greenberg, M. Ivanov, M. Pushkin, A. Inozemtsev, A. Patselov, A.
Tankeyev, S. Kuzmin, V. Lysak, Formation of intermetallic com-
pounds during explosive welding, Met. and Mat. Tran. A, 47 (2016),
5461–5473, doi:10.1007/s11661-016-3729-7
21
I. Bataev, D. Lazurenko, S. Tanaka, K. Hokamoto, A. Bataev, Y.
Guo, A. Jorge Junior, High cooling rates and metastable phases at the
interfaces of explosively welded materials, Acta Mat., 135 (2017),
277–289, doi:10.1016/j.actamat.2017.06.038
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