A. DEBIH: INFLUENCE OF A TOOL’S ROTATIONAL SPEED ON THE MECHANICAL PROPERTIES OF ...
637–645
INFLUENCE OF A TOOL’S ROTATIONAL SPEED ON THE
MECHANICAL PROPERTIES OF FRICTION-STIR-WELDED JOINTS
OF DISSIMILAR AA6082 AND AA5052 ALUMINIUM ALLOYS
VPLIV HITROSTI VRTENJA ORODJA NA MEHANSKE LASTNOSTI
ZVARNIH SPOJEV IZ RAZLI^NIH ZLITIN NA OSNOVI ALUMINIJA,
IZDELANIH Z VRTILNO-TORNIM POSTOPKOM VARJENJA
Ali Debih
Mechanical department, University of M’sila, M’sila, 28000, Algeria
Prejem rokopisa – received: 2024-07-06; sprejem za objavo – accepted for publication: 2024-08-28
doi:10.17222/mit.2024.1238
This study examines the influence of a tool’s rotational speed on the microstructure and mechanical properties of dissimilar fric-
tion-stir-welded joints of AA6082 and AA5052 aluminium alloys. The joining process was carried out at various rotational
speeds of 600 min
–1
, 1000 min
–1
, and 1400 min
–1
and a constant welding speed of 35 mm/min using a high-speed-steel
(HSS-Co5) tool with a cylindrical pin. The microstructure of the welded joints was characterized using optical microscopy. The
Vickers microhardness, tensile properties, and impact strength of welded joints were evaluated and compared to base metals.
Results showed that the mechanical properties and the joint performance were considerably influenced by the tool’s rotational
speed due to the amount of heat input and the formation of macroscopic defects in the stir zone. It was found that a rotational
speed of 1000 min
–1
is the suitable welding parameter for optimum mechanical properties. The welded joint at 1000 min
–1
shows
a tensile strength of 122 MPa, elongation of 8.1 %, specific impact strength of 0.43 J/mm
2
, and a maximum microhardness of 75
HV in the stir zone. In all welded joint samples, the fracture locations were near the edge of the welded zone on the retreating
side. The results provide further insight into the appropriate selection of FSW process parameters that ensure excellent joints be-
tween AA5052 and AA6082 alloys with the required mechanical properties.
Keywords: aluminium alloys, friction stir welding, mechanical properties, microstructure
V ~lanku avtor opisuje raziskavo vpliva parametrov hitrosti vrtenja orodja na mikrostrukturo in mehanske lastnosti zvarnih
spojev med dvema razli~nima tipoma Al zlitin; to je AA6082 in AA5052. Zvarni spoji so bili izdelani s tako imenovanim
vrtilno/me{alnim postopkom trenjskega varjenja (FSW; angl.: friction stir welding). Varjenje je bilo izvr{eno pri razli~nih
hitrostih vrtenja orodja 600 min
–1
, 1000 min
–1
in 1400 min
–1
. Hitrost varjenja je bila konstantna 35 mm/min in orodje je imelo
cilindri~no konico iz hitroreznega jekla vrse HSS-Co5. Za karakterizacijo mikrostrukture je avtor uporabil svetlobni
metalografski mikroskop. Izmerjeno Vickersovo mikrotrdoto, natezne lastnosti in udarno `ilavost je avtor primerjal z
vrednostmi dobljenimi pri osnovnih dveh materialih. Rezultati preiskav in meritev so pokazali, da so na lastnosti zvarov mo~no
vplivale razli~ne hitrosti vrtenja orodja zaradi razli~nega vnosa toplote in tvorbe makroskopskih napak v conah vrtenja orodja.
Avtor ugotavlja, da je hitrost vrtenja 1000 min
–1
najbolj primerna hitrost vrtenja orodja za doseganje optimalnih mehanskih
lastnosti zvarov. Pri hitrosti 1000 min
–1
so bile v coni vrtenja orodja dose`ene naslednje vrednosti: natezna trdnost 122 MPa,
raztezek 8,1 %, specifi~na udarna `ilavost 0,43 J/mm
2
in maksimalna Vickersova mikrotrdota 75 HV. Pri vseh preizku{ancih je
pri{lo do njihovega loma na robu (blizu) cone varjenja po ponovni toplotni obdelavi. Avtor verjame, da predstavljeni dosedanji
rezultati preiskave omogo~ajo nadaljnjo pomo~ pri izbiri parametrov FSW procesa varjenja, ki dajejo odli~en zvarni spoj med
zlitinama AA5052 in AA6082 z zahtevanimi mehanskimi lastnostmi.
Klju~ne besede: zlitine na osnovi aluminija, vrtilno/me{alni trenjski postopek varjenja, mehanske lastnosti, mikrostruktura
1 INTRODUCTION
Aluminium alloys are commonly used in many
emerging fields such as automobile, aerospace, marine,
and medical industries owing to their high strength-to-
weight ratio and good formability.
1–7
For example, sub-
stituting steel with aluminium can result in a weight re-
duction of up to 40 %.
1,4
However, aluminium alloys are
often categorized as difficult to weld using fusion weld-
ing because of their high thermal conductivity, low melt-
ing point, affinity for oxygen and hydrogen, poor solidi-
fication microstructure, and porosity in the fusion
zone.
8–11
While the production of aluminium components
is not very complex, the fusion welding of these alloys
can present problems and challenges due to the excellent
thermal and electrical conductivity, and the lack of struc-
tural transformation in the solid state.
11–13
Friction stir welding (FSW) is an innovative,
solid-state welding technology that is widely used for
both the similar and dissimilar joining of aluminium al-
loys. The FSW process has advantages over traditional
fusion welding processes in terms of better mechanical
properties, low residual stress, and reducing micro-
structural defects.
8,9,14–16
Furthermore, FSW can be used
in place of riveting on industrial components to save
weight and production time, thus leading to a reduction
in cost. The peculiarity of the FSW process is reflected
in public health and the environment protection, as well
Materiali in tehnologije / Materials and technology 58 (2024) 5, 637–645 637
UDK 669.715:621.791.1 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 58(5)637(2024)
*Corresponding author's e-mail:
ali.debih@univ-msila.dz (Ali Debih)

as workplace safety, as it does not produce any harmful
fumes, gases and radiation and is also safe for opera-
tors.
5,17
The FSW process uses a spinning, non-consumable
cylindrical tool with a profiled pin and shaped shoulder
to generate frictional heat in the joined piece.
18
Heat is
generated between the tool and material, and then me-
chanically intermixes the two pieces at the weld line,
hence the softened metal, without reaching melting
point, can be joined using mechanical pressure.
19–23
The
side where the rotational direction and the welding direc-
tion coincide is called the advancing side (AS), while the
opposite side is defined as the retreating side (RS).
A complex microstructure, comprising the stir zone
(SZ), heat-affected zone (HAZ), thermo-mechanically
affected zone (TMAZ), and base metal (BM), is often
created during FSW depending on the level of strain and
the temperature cycle.
1,24–27
In BM, the metal is charac-
terized by no change in the structure and mechanical
properties. In the HAZ, the material is only affected by
the heat generated during welding. The TMAZ is charac-
terized by a highly deformed microstructure since the
material suffers from plastic deformation and insufficient
heating for dynamic recrystallization (DRX). In the SZ,
the metal that experiences both severe plastic deforma-
tion and high temperature leads to an excellent grain re-
finement owing to complete DRX process.
The strength and quality of the weld are typically de-
termined by the heat produced and the material mixed
during the welding process. Consequently, the FSW pro-
cess parameters, including tool geometry, tool rotation
speed, and axial load play a role in controlling the joint
characteristics. Furthermore, the location of dissimilar
base metals on the retreating or advancing sides affects
the quality of the joint.
18,26
For industrial applications, the mechanical and physi-
cal characteristics of welded aluminium alloys are of pri-
mary importance. In this context, numerous research pro-
jects have studied the FSW of dissimilar Al alloys joints
focusing on the effect of process parameters and process
optimization.
28–31
For instance, Kumbhar et al.
29
investi-
gated the effect of the nugget zone microstructure on the
mechanical properties of dissimilar FSW joints of
AA5052-H32 and AA6061-T6 alloys. Their results
showed that the inter-diffusion of alloying elements and
the attainment of similar orientations in the nugget could
have contributed to the good mechanical properties of
the specimens. Lee et al.
30
investigated the effect of FSW
parameters on the normal load and spindle torque during
the welding of dissimilar AA5052-H112 and
AA6061-T6 alloys. They found that the interface
morphologies were characterized by interface pull-up
and pull-down on the advancing side and retreating side.
Although studies that have been published in the lit-
erature demonstrate that AA5052 and AA6082 alloys
can be joined successfully using FSW technology, the ki-
nematic parameters have a role in the FSW process.
Hence in this investigation, an attempt was carried out in
this area of research to understand the effect of rotational
tool speed on the performance of FSW dissimilar
AA6082 and AA5052 alloys. Three rotational speeds of
600 min
–1
, 1000 min
–1
and 1400 min
–1
were used to ob-
tain dissimilar AA6082 and AA5052 welds joints.
Macrostructure, microstructure evolutions, microhard-
ness, tensile and impact strength tests were carried out
using an optical microscope, Vickers microhardness, ten-
sile, and impact strength tests.
2 MATERIALS AND METHODS
The materials were rolled sheets of AA 6082 and AA
5052 aluminium alloys with 8 mm of thickness. The
chemical compositions of the alloys are in Table 1.
The plates were slashed and milled into the required
rectangular size of 150 mm × 50 mm × 8 mm, then
grinded with abrasive paper of 1200 grit to achieve a su-
perior surface finish. In the case of dissimilar butt join-
ing, it has been demonstrated that better mechanical
properties are obtained when harder material is placed on
the advancing side (AS) and softer material is positioned
on the retreating side (RS).
18,26
Accordingly, the AA5052
plate was placed on the AS due to its higher mechanical
strength, and the AA6082 plate was placed on the RS.
The workpieces were arranged in a butt rectangular con-
figuration, positioned in the fixture to avoid the separa-
tion of the plates during welding. The FSW was carried
out using a universal milling machine (HURON). The
welding tool used in this study was made of high-speed
steel (HSS-Co5), which has high resistance to elevated
temperatures. It has a cylindrical geometry with a shoul-
der diameter of 20 mm, and a pin diameter of 7 mm,
while the length of the pin was 7.8 mm, as was the re-
quired welding depth of the plates with a tilt angle of 2°.
Friction stir welds were carried out along the longitudi-
nal direction of the plate at 600 min
–1
, 1000 min
–1
, and
1400 min
–1
as the tool’s rotational speeds, keeping the
constant traverse welding speed of 35 mm/min.
The microstructural observations were carried out us-
ing an optical microscope (Olympus A13.1031-B) with
digital resolution at higher magnification. The samples
for microstructural examination were prepared using
Keller’s reagent (180 mL distilled water+2mLHF+2
mLHCl+2mLHNO
3
).
A. DEBIH: INFLUENCE OF A TOOL’S ROTATIONAL SPEED ON THE MECHANICAL PROPERTIES OF ...
638 Materiali in tehnologije / Materials and technology 58 (2024) 5, 637–645
Table 1: Chemical composition in weight percentage (w/%) of AA6082 and AA5052 BM
Alloy Si Cr Mg Mn Ni Cu Zn Fe Al
AA6082 0.91 0.04 0.85 0.41 0.003 0.1 0.009 0.21 Balance
AA5052 0.17 0.11 2.31 0.08 0.02 0.09 0.03 0.23 Balance

Scanning electron microscopic observations (SEM)
and energy-dispersive X-ray spectroscopy (EDS analy-
sis) were performed using a JEOL-JSM 7001F micro-
scope.
XRD analysis was conducted using an X’pert PRO
diffractometer from PANalytical, equipped with Cu-Ka
radiation. X-ray measurements were performed at 35 kV
and a current of 20 mA. The wavelength K
 1
= 0.15418
nm was used for calculations. The general view of the
X-ray patterns was taken with a scanning step of 0.02° in
the range of 2 angles from 10° to 90°. The X-ray pat-
terns were analysed by X’Pert High Score plus and iden-
tified by the (Pcpdfwin database (JCPDS-ICDD) soft-
ware.
The Vickers microhardness profiles were obtained on
the longitudinal cross-section of each sample using a
TUKON 2500 with a 0.5 N load for 15 s and a spacing of
0.5 mm along the mid-thickness line.
Samples for the tensile test were cut using an elec-
tro-discharge machine with dimensions of a gauge length
of 25 mm, a thickness of 7 mm, and a gauge width of
6 mm. Tensile tests were performed at room temperature
to fracture using a hydraulic testing machine at a strain
rate of 10
–3
s
–1
. Three samples were tested for each rota-
tional speed condition, with the averaged experimental
data considered the final result.
Impact tests were conducted at room temperature on
specimens having a length of 55 mm, width of 10 mm,
and thickness of 7 mm using an impact-testing machine
"Instron Wolpert" type with a maximum capacity of
300 J. For each rotational speed condition, at least three
impact specimens were tested to determine the amount
of energy absorbed during fracture and determine the
specific impact toughness of the weld plates.
3 RESULTS AND DISCUSSION
3.1 Macrostructure and microstructure inspection
Figure 1 shows the top and root surface morphol-
ogies of the weld joints at 600 min
–1
, 1000 min
–1
, and
1400 min
–1
, respectively. The welding directions, AS and
RS are indicated in the same figure. A smooth weld and
a good surface appearance are obtained with increasing
the rotation speed due to the increase in heat input and
material flow during stirring. A smooth weld and less
surface appearance were obtained at the lowest value of
rotation speed (600 min
–1
) due to low temperature and
low material flow, as shown in Figure 1a. The lower lat-
eral flash was observed on the weld surface at a tool ro-
tation speed of 1000 min
–1
(Figure 1b). However, exces-
sive lateral flash and grooves were observed on the
retreating side (RS) of the butt joint, especially at the
highest value of the tool rotation speed (1400 min
–1
)re -
sulting from the outflow of plasticized material from un-
derneath the shoulder, as shown in Figure 1c. Fig-
ures 1d–1f show line defects as well as incomplete
penetration on the root surfaces of the weld joints at all
the welding rotational speeds. The occurrence of these
defects indicates that a portion of the joint root is not
completed and filled with weld metal. These defects re-
duce the quality of welding joints and impact the manu-
facturing cost of the workpieces.
3,31–33
Figure 2 presents the morphology of the cross-sec-
tion of the welded joint at 600 min
–1
, 1000 min
–1
, and
1400 min
–1
. The macroscopic defects appeared at the
lowest (600 min
–1
) and highest (1400 min
–1
) tool rota-
tional speeds. The formation of tunnel defect at the low
tool rotation speed, as shown in Figure 2a, is probably
caused by the inferior metal flow during the welding.
While the groove defects observed in the weld joint at
high tool rotation speed, as presented in Figure 2c,re-
sulted from the outflow of the plasticized material from
underneath the shoulder.
Joint strength decreases as the size of the tunnels and
grooves increases. Joints having large grooving or tun-
nelling defects possessed lower mechanical properties
and vice-versa. The cross-section of the welded joint at
1000 min
–1
showed a typical FSW morphology without
defects, for these reasons the samples welded at
1000 min
–1
were chosen for the microstructural analysis.
A. DEBIH: INFLUENCE OF A TOOL’S ROTATIONAL SPEED ON THE MECHANICAL PROPERTIES OF ...
Materiali in tehnologije / Materials and technology 58 (2024) 5, 637–645 639
Figure 1: Top and root surface macrostructure of the weld joint at: a) and d) 600 min
–1
, b and e) 1000 min
–1
, c and f) 1400 min
–1

A. DEBIH: INFLUENCE OF A TOOL’S ROTATIONAL SPEED ON THE MECHANICAL PROPERTIES OF ...
640 Materiali in tehnologije / Materials and technology 58 (2024) 5, 637–645
Figure 3: Microstructures of the different regions; a) regions of optical observations, b) 6082 base metal, c) 5052 base metal. d) Interface
HAZ-TMAZ of 6082, e) TMAZ of 6082, f) TMAZ of 6082, g) interface HAZ-TMAZ of 5052, h) HAZ of 5052, i) TMAZ of 5052, j) Nugget
zone
Figure 2: Cross-section morphology of the welds joint at: a) 600 min
–1
, b) 1000 min
–1
, and c) a groove-like defect revealed on the top surface of
the weldment at 1400 min
–1

As marked in Figure 2b, the weld joint at 1000 min
–1
is
divided into four characteristic regions, BM, HAZ,
TMAZ and the weld zone or SZ. More details on the
microstructural characteristics of these regions are de-
picted in Figure 3.
The microstructures of AA 6082 and AA 5052 BM
are shown in Figures 3b and 3c, respectively. AA 6082
and AA 5052 alloys exhibit a typical rolled, deformed
microstructure with elongated grains having average di-
mensions of 70 × 25 μm and 30 × 19 μm, respectively
with the presence of second-phase particles along the
rolling direction. SEM micrographs (Figure 4), EDS re-
sults (Table 2) and XRD pattern (Figure 5) indicated
that the second phases present in the AA5052 alloy were
Mg
2
Si and Al
6
Mn phases. While the second phases iden-
tified in the AA6082 alloy were Mg
2
Si and Al(FeSi)
phases.
Figures 3d and 3g depict distinguishable micro-
graphs at the interfaces joint between the HAZ-TMAZ
zones on the RS and AS, respectively. It is observed
from Figure 3e that the microstructure of the HAZ on
the RS becomes more equiaxed and refined with an aver-
age size of 40 μm than the AA6082 BM. It appears that
the thermal cycle occurred in the HAZ help the recryst-
allization of rolled, deformed AA6082 BM. Figure 3f
shows a typical microstructure of the TMAZ region of
the RS, which is obviously more refined (26 μm) than
that of the HAZ microstructure.
Figure 3h presents the microstructure of the HAZ on
the AS, which is characterized by equiaxed grains but
with large mean grain size of 100 μm. It is evident that
the AA5052 alloy is more sensible to heat input than the
AA6082 alloy. The microstructure of the TMAZ on the
AS shown in Figure 3i exhibits more refined grains with
a mean grain size of 50 μm than the HAZ due to high
plastic strain induced by stirring. Figure 3j shows the
microstructure of the SZ, which consists of extremely re-
fined grains due to the occurrence of DRX. In this area,
the AA6082 and AA5052 alloys were more thoroughly
mixed than in the other regions.
3.2 Mechanical properties
We provide all the Vickers microhardness values for
the base metals and the welded zones with a test load of
0.5 N and duration of 15 s. Figure 6 shows the variation
A. DEBIH: INFLUENCE OF A TOOL’S ROTATIONAL SPEED ON THE MECHANICAL PROPERTIES OF ...
Materiali in tehnologije / Materials and technology 58 (2024) 5, 637–645 641
Figure 5: XRD spectra for base metals AA 6082, AA 5052 and NZ of
FSW AA6082/AA5052 at different tool rotational speeds
Figure 4: SEM micrographs in the NZ of dissimilar: a) AA 6082, b) AA 5052
Table 2: EDS analyses of the weld region microstructure (w/%)
Materials Al Mg Si Mn Fe Possible phase
AA 6082
Spot 1 – 68.4 31.6 – – Mg
2
Si
Spot 2 62.21 1.3 13.2 0.19 23.1  (AlFeSi)
Spot 3 79.1 1.7 3.71 0.13 6.21  Al(FeSi)
AA 5052
Spot 4 – 71.3 28.7 – – Mg2
Si
Spot 5 81.65 – – 18.35 – Al6
Mn

of microhardness as a function of distance from the weld
centre for the joints at 600 min
–1
, 1000 min
–1
,a n d
1400 min
–1
. For comparison, the microhardness values of
the AA 5052 (80 HV) and AA 6082 (35 HV) BM are
displayed in the plot. The microhardness across the weld
zones of all the samples is considerably lower than that
of the AA5052 BM and comparatively higher than that
of the AA6082 BM. It can be concluded that dissimilar
joints present an intermediate behaviour.
In the SZ, the lowest microhardness value was re-
corded in the centre of the weld joint at 600 min
–1
(38 HV), 1000 min
–1
(57 HV) and 1400 min
–1
(55 HV).
Then, the microhardness increases with increasing dis-
tance from the weld centre to reach a maximum of
56.8 HV at 3.5 mm from the weld centre at 600 min
–1
,a
75 HV at –2 mm form the centre of the weld joint at
1000 min
–1
, and 59.6 HV at –2.5 mm from the weld cen-
tre of the weld joint at 1400 min
–1
, respectively. The rise
in microhardness is attributed to the grain refinement and
the formation of the second Mg
2
Si and AlFeSi phases in
the welding zone.
In the RS, the microhardness gradually decreases
with increasing distance from the weld centre along the
TMAZ and HAZ regions. It is interesting to note that the
weld joint at 1000 min
–1
exhibits the highest microhard-
ness values. The high microhardness values near the pin
diameter can be attributed to the grain refinement caused
by intensive stirring during the FSW. In contrast, the
microhardness along the distance from the weld centre in
the AS did not change with changing the tool rotational
speed. The highly asymmetrical microhardness distribu-
tion along the cross-section of the welded joints was due
to the different microstructural zones of both sides,
which develop due to the thermo-mechanical history dur-
ing elaboration and welding.
Figure 7 presents the stress-strain curves of the BM
and weld joints at 600 min
–1
, 1000 min
–1
,a n d
1400 min
–1
. Table 3 summarizes the tensile properties
including the tensile strength (UTS), 0.2 % yield strength
(YS), elongation at break (A %), and joint efficiency (%).
The joint efficiency is calculated based on the FSW joint
strength relative to the strength of the base metals. Addi-
tionally, micrographs showing the failure locations of
tensile specimens after testing are presented in Figure 8.
The results demonstrate that the tensile properties of the
welded joints fluctuated with respect to different rota-
tional speeds. The AA5052 BM alloy presents a higher
yield strength and a higher tensile strength, but a lower
percentage of elongation. For the welded specimens, it
was found that dissimilar joints obtained at 1000 min
–1
exhibited good tensile properties. In contrast, joints ob-
tained at 600 min
–1
and 1400 min
–1
showed lower
strengths compared to AA6082 and AA5052 BM. It is
interesting to note that all the joints fractured near the
weld edge in the HAZ-TMAZ zone along the RS, as
shown in Figure 8. This was due to the lower yield
A. DEBIH: INFLUENCE OF A TOOL’S ROTATIONAL SPEED ON THE MECHANICAL PROPERTIES OF ...
642 Materiali in tehnologije / Materials and technology 58 (2024) 5, 637–645
Figure 7: Stress–strain curves for AA 6082, AA 5052 BM and weld
joint at 600 min
–1
, 1000 min
–1
and 1400 min
–1
Figure 6: Microhardness evolution as a function of distance from the
weld centre for the weld joint at 600 min
–1
, 1000 min
–1
,a n d
1400 min
–1
. The microhardnesses of AA6082 and AA5052 BM are
given for comparison. Figure 8: Failure locations of transverse tensile specimens

A. DEBIH: INFLUENCE OF A TOOL’S ROTATIONAL SPEED ON THE MECHANICAL PROPERTIES OF ...
Materiali in tehnologije / Materials and technology 58 (2024) 5, 637–645 643
Figure 9: Impact energy fracture surface of specimens. a) base metal 6082, b) FSW at 600 min
–1
, c) FSW at 1000 min
–1
, d) lateral view of the
base metal 6082 impact specimen, e) lateral view of the FSW specimen at 600 min
–1
, f) lateral view of the FSW specimen at 1000 min
–1
, g) frac-
ture surface of base metal 5052, h) FSW at 1400 min
–1
, i) lateral view of the base metal 5052 impact specimen and j) lateral view of the FSW
specimen at 1400 min
–1
Table 3: Tensile test results and specific impact energy values of AA 6082 and AA 5052 welded specimens
Condition UTS,MPa YS,MPa A, % Joint efficiency, %
Specific impact en-
ergy, (J/mm
2
)
AA6082 BM 127 59 27 – 0.71
AA5052 BM 265 194 9.7 – 0.32
FSW at 600 min
–1
95 47 3.4 36–75 0.49
FSW at 1000 min
–1
122 57 8.1 46–96 0.43
FSW at 1400 min
–1
111 55 8.7 41–87 0.19

strength of the AA6082 alloy compared to the AA5052
alloy in the AS.
The welded joint at 600 min
–1
exhibits the lowest ten-
sile strength and ductility of 95 MPa and 3.4 %, respec-
tively. This reveals that the heat generated by the weld-
ing at 600 min
–1
was insufficient to plasticize the metals,
leading to the formation of tunnel and void defects. The
welded joint at 1000 min
–1
had a tensile strength of
122 MPa and an elongation to failure of 8.1 %. The im-
provement in the mechanical properties is a consequence
of the microstructural evolution. Indeed, the micro-
structural examination of the weld joint at 1000 min
–1
showed that the SZ exhibits a refined grains structure
without defects in which the AA5052 and the AA6082
metals were properly mixed. The tensile strength of the
welded joint at 1400 min
–1
decreased to 111 MPa, but
showed good ductility (8.7 %). This reveals that the fric-
tion generated by the tool produces excessive heat, mak-
ing the metal too plastic, resulting in good ductility, but
also producing excessive grooves and lateral flash, as
shown in Figures 1 and 2. This happened due to the im-
proper mixing of the metals in the welded zone.
The tensile properties of the joints are affected by the
welding rotation speed, and they are very close to the
AA6082 BM on the RS. The ultimate strength efficiency
for the 5052–6082 joints, produced at 600 min
–1
,
1000 min
–1
, and 1400 min
–1
, was 75 %, 96 %, and 87 %
compared to the base metal AA 6082 alloy. Specimens
of base metal 5052 present the lowest ductility compared
to that of AA 6082, with 10 % as a percentage of elonga-
tion. The ductility is reduced by 17 % for the specimens
welded at 1000 min
–1
. The percentage of elongation of
specimens processed at 1400 min
–1
is observed to be
8.7 %, whereas only 3.4 % of elongation is observed for
specimens processed at 600 min
–1
. It can be determined
from the relation between the tensile properties and
welding parameters that the rotation speed and welding
speed designed at 1000 min
–1
and 35 mm/min are opti-
mum for the ultimate strength.
The specific impact energy values of AA6082 BM,
AA5052 BM, and welded joint at 600 min
–1
, 1000 min
–1
,
and 1400 min
–1
are given in Table 3. The specific impact
energy decreased from 0.49 J/mm
2
to 0.19 J/mm
2
when
the rotational tool speed increased from 600 min
–1
to
1400 min
–1
. The loss in specific impact energy at high
rotational tool speed may be due to high heat input, re-
sulting in a coarse-grained structure, the presence of de-
fects and improper bonding in the welded zone. The lat-
eral view and appearance of the fracture surface of the
samples after the impact strength test are shown in Fig-
ure 9. The lateral view of AA6082 BM, weld joint at
600 min
–1
and 1000 min
–1
demonstrated that these sam-
ples did not break after the impact-strength test, reveal-
ing that the FSW joint did not lose its ductility (Fig-
ures 9a–9c). The fracture surface appearance of AA6082
BM exhibits a typical shear lips morphology, which is a
characteristic of ductile material. A tunnel is visible in
the fracture surface appearance of weld joint sample at
600 min
–1
,( Figure 9b). While the surface appearance of
the sample weld joint at 1000 min
–1
is smoother. Figures
9g–9j show that the AA5052 BM and the weld joint at
1400 min
–1
fractured after the impact strength test. Since
the AA5052 BM is a brittle alloy, its fracture surface ap-
peared as a flat smooth fracture, while grooves are visi-
ble in the fracture surface of the weld joint at 1400 min
–1
,
as shown in Figure 9h.
4 CONCLUSIONS
The present work investigated the impact of a tool’s
rotational speed on the mechanical properties of the
FSW dissimilar AA 5052 and AA6082 alloys. From the
experimental results, the following conclusions are
drawn:
• The joint of dissimilar AA 5052 and AA6082 alloys
was successfully performed using FSW processing at
tool rotational speeds of 600 min
–1
, 1000 min
–1
and
1400 min
–1
and a constant welding speed of
35 mm/min using a cylindrical pin.
• Due to insufficient and excess heat input, tunnel and
groove defects developed in the weld joints at
600 min
–1
and 1400 min
–1
, respectively. In contrast,
FSW at 1000 min
–1
produced a defect-free weld joint
composed mainly of SZ, TMAZ, HAZ and BM.
• The microhardness distribution along the cross-sec-
tion of the welded joints was highly asymmetrical
due to the microstructural heterogeneity produced
during FSW and the dissimilar AA 5052 and
AA6082 BM alloys. The microhardness in the centre
of the stir zone was found around 38 HV at
600 min
–1
, 57 HV at 1000 min
–1
,5 5H Va t
1400 min
–1
.
• Optimum mechanical properties were obtained dur-
ing FSW with a rotational speed of 1000 min
–1
. The
welded joint at 1000 min
–1
shows a tensile strength of
122 MPa, elongation of 8.1 %, and specific impact
strength of 0.43 J/mm
2
.
• The fractures of all the weld-joint samples during the
tensile test were located on the retreating side at the
softest points of the HAZ-TMAZ zone.
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