Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys
Cast aluminum alloy, AC4CH-T6, and wrought aluminum alloy, A6061-T6, werejoined by means of friction stir welding (FSW) technique. The effect of microstructure and post heat treatment on fatigue behavior of the dissimilar joints was investigated. Near the weld centre, Vickers hardness was lower than...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
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nasplib_isofts_kiev_ua-123456789-484202025-02-23T18:10:59Z Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys Усталость соединений, полученных сваркой трением, различных алюминиевых сплавов: литых и обработанных давлением Uematsu, Y. Tozaki, Y. Tokaji, K. Nakamura, M. Научно-технический раздел Cast aluminum alloy, AC4CH-T6, and wrought aluminum alloy, A6061-T6, werejoined by means of friction stir welding (FSW) technique. The effect of microstructure and post heat treatment on fatigue behavior of the dissimilar joints was investigated. Near the weld centre, Vickers hardness was lower than in the parent metals and the hardness minima were observed along the trace route ofFSW tool’s shoulder edge. Tensilefracture tookplace on A6061 side where the hardness was minimal, resulting in the lower static strength of the dissimilar joints than AC4CH or A6061. Fatigue fracture occurred on AC4CH side due to casting defects and the fatigue strength of the dissimilarjoints was similar to that of AC4CH, but lower than that of A6061. Friction stirprocess (FSP) andpost heat treatment successfully improved thefatigue strength of the dissimilarjoints up to that of the parent metal, A6061. Испытания на круговой изгиб для оценки сопротивления усталости проводили на воздухе и в дистиллированной воде на трех экструзивных магниевых сплавах AZ80, AZ61 и AM60 различного химического состава. На воздухе сопротивление усталости при высоких уровнях напряжений было при мерно одинаковым для всех сплавов, поскольку трещины зарождались у интерметаллических соединений Al-Mn, тогда как AZ80 с наибольшим содержанием Al имел наибольшее сопротивление усталости при низких уровнях напряжений, что объясняется зарождением трещин вследствие циклической деформации скольжения в микроструктуре матрицы. В дистиллированной воде сопротивление усталости значительно снижалось за счет образования коррозионных язв во всех сплавах, а различие в сопротивлении усталости при низких уров нях напряжений отсутствовало, указывая на то, что добавка Al, улучшавшая сопротивление усталости на воздухе, оказывала отрицательное воздействие на коррозионную усталость. 2008 Article Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys / Y. Uematsu, Y. Tozaki, K. Tokaji, M. Nakamura // Проблемы прочности. — 2008. — № 1. — С. 150-154. — Бібліогр.: 3 назв. — англ. 0556-171X https://nasplib.isofts.kiev.ua/handle/123456789/48420 539.4 en Проблемы прочности application/pdf Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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Научно-технический раздел Научно-технический раздел |
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Научно-технический раздел Научно-технический раздел Uematsu, Y. Tozaki, Y. Tokaji, K. Nakamura, M. Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys Проблемы прочности |
| description |
Cast aluminum alloy, AC4CH-T6, and wrought aluminum alloy, A6061-T6, werejoined by means of friction stir welding (FSW) technique. The effect of microstructure and post heat treatment on fatigue behavior of the dissimilar joints was investigated. Near the weld centre, Vickers hardness was lower than in the parent metals and the hardness minima were observed along the trace route ofFSW tool’s shoulder edge. Tensilefracture tookplace on A6061 side where the hardness was minimal, resulting in the lower static strength of the dissimilar joints than AC4CH or A6061. Fatigue fracture occurred on AC4CH side due to casting defects and the fatigue strength of the dissimilarjoints was similar to that of AC4CH, but lower than that of A6061. Friction stirprocess (FSP) andpost heat treatment successfully improved thefatigue strength of the dissimilarjoints up to that of the parent metal, A6061. |
| format |
Article |
| author |
Uematsu, Y. Tozaki, Y. Tokaji, K. Nakamura, M. |
| author_facet |
Uematsu, Y. Tozaki, Y. Tokaji, K. Nakamura, M. |
| author_sort |
Uematsu, Y. |
| title |
Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys |
| title_short |
Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys |
| title_full |
Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys |
| title_fullStr |
Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys |
| title_full_unstemmed |
Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys |
| title_sort |
fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys |
| publisher |
Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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2008 |
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Научно-технический раздел |
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https://nasplib.isofts.kiev.ua/handle/123456789/48420 |
| citation_txt |
Fatigue behavior of dissimilar friction stir welds between cast and wrought aluminum alloys / Y. Uematsu, Y. Tozaki, K. Tokaji, M. Nakamura // Проблемы прочности. — 2008. — № 1. — С. 150-154. — Бібліогр.: 3 назв. — англ. |
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Проблемы прочности |
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2025-11-24T07:38:09Z |
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| fulltext |
UDC 539. 4
F a t ig u e B e h a v io r o f D is s im ila r F r ic t io n S t ir W e ld s b e tw e e n C a s t a n d W r o u g h t
A lu m in u m A llo y s
Y . U em a tsu ,1a Y . T ozak i,2 K . T o k a ji,1b and M . N a k a m u ra 1
1 Gifu University, Gifu, Japan
2 Gifu Prefectural Research Institute for Machinery and Materials, Seki, Japan
a yuematsu@gifu-u.ac.jp, b tokaji@gifu-u.ac.jp
Cast aluminum alloy, AC4CH-T6, and wrought aluminum alloy, A6061-T6, were joined by means o f
friction stir welding (FSW) technique. The effect o f microstructure and post heat treatment on
fatigue behavior o f the dissimilar joints was investigated. Near the weld centre, Vickers hardness
was lower than in the parent metals and the hardness minima were observed along the trace route
o f FSW too l’s shoulder edge. Tensile fracture took place on A6061 side where the hardness was
minimal, resulting in the lower static strength o f the dissimilar joints than AC4CH or A6061.
Fatigue fracture occurred on AC4CH side due to casting defects and the fatigue strength o f the
dissimilar joints was similar to that o f AC4CH, but lower than that o f A6061. Friction stir process
(FSP) and post heat treatment successfully improved the fatigue strength o f the dissimilar joints up
to that o f the parent metal, A6061.
K eyw ords: fatigue, friction stir w eld ing, dissim ilar joint, alum inum alloy.
In trod u ction . A lum inum alloys are increasingly used for transportation system s,
particularly in autom obiles, w ith the aim o f w eight saving. W rought and cast aluminum
alloys are applied to body skin and com plex shape com ponents, respectively, and join ing
betw een both alloys is often required. Friction stir w eld ing (F SW ) is a recently developed
solid state w eld ing process and n ow being used for jo in ing aluminum alloys for w hich
fusion w eld ing is d ifficult [1 , 2]. Furthermore, it is know n that FSW technique is suitable
for jo in ing dissim ilar m etals because o f solid state process [3]. In order to apply dissim ilar
jo ints to load-bearing com ponents, it is significant to understand their fatigue behavior. In
the present study, the fatigue behavior o f the dissim ilar FSW joints betw een cast
alum inum alloy, A C 4C H -T 6 and w rought alum inum alloy, A 6061-T 6, w as investigated.
The effect o f microstructure and post heat treatment on fatigue behavior is discussed.
E xp er im en ta l D eta ils. M ateria ls. The materials used are cast alum inum alloy,
A C 4C H -T 6, and wrought aluminum alloy, A 6061-T 6. Their chem ical com positions
(wt.% ) and m echanical properties are listed in Tables 1 and 2, respectively. The
microstructures o f the parent m etals are show n in Fig. 1. A typical dendrite structure o f
cast aluminum alloy is recognized in A C 4C H (Fig. 1a), w hile elongated grains due to
rolling process are seen in A 6061 (Fig. 1b), where the average grain size m easured along
the rolling direction w as about 90 ,«m.
W elding C ondition an d Specim en. Plates w ith a thickness o f 5 m m w ere cut from
casting b locks o f A C 4C H by w ire cut electric spark m achining. A C 4C H plates were butt
w eld ed w ith A 6061 plates o f the sam e thickness by FSW technique to form the stock from
w hich fatigue specim ens were machined. The upper and low er skins o f the stock were
rem oved by 0.5 mm depth by m illing process. The configuration o f fatigue specim ens is
show n in Fig. 2. The centre o f the gauge section corresponds to the w eld ing line and the
loading direction is perpendicular to the w eld ing direction. The friction stir tool w as
com posed o f a pin and a shoulder w h ose diameter is 6 and 14 m m , respectively. The
tool-to-w orkpiece angle w as 3° from the vertical axis. The plates were jo ined w ith the tool
travel speed o f 150 m m /m in and the tool rotational speed o f 1000 rpm. A 6061 was
arranged on the advancing side (A S) w here the tool travel direction coincides w ith the
© Y. U EM A TSU , Y. T O ZA K I, K. TO K A JI, M. N A K A M U R A , 2008
150 ISSN 0556-171X. Проблемы прочности, 2008, № 1
mailto:yuematsu@gifu-u.ac.jp
mailto:tokaji@gifu-u.ac.jp
Fatigue Behavior o f Dissimilar Friction Stir Welds
T a b l e 1
Chemical Compositions of Materials
Material Si Mg Zn Fe Ni Ti Sr Cu Mn Cr
AC4CH-T6
A6061-T6
7.10
0.58
0.36
0.96
0.01
0.02
0.12
0.41
0.022 0.11
0.04
0.005
0.28 0.03 0.23
T a b l e 2
Mechanical Properties of Materials
Material 0.2% proof stress Tensile strength Elongation Elastic modulus
a 0 2, MPa аъ , MPa &,% E , GPa
AC4CH-T6 165 230 5.2 72.5
A6061-T6 275 310 12.0 68.3
Fig. 1. Microstructures o f parent metals: (a) AC4CH, (b) A6061.
Fig. 2. Configuration o f fatigue specimen.
tool rotational direction. D issim ilar joints, in w hich A 6061 w as arranged on the retreating
side (R S), w ere also exam ined, but there existed no notable differences in microstructure,
hardness profile and tensile strength.
The fatigue fracture o f the as-w elded joints took place on A C 4C H side due to
casting defects. Therefore, friction stir process (FSP) w as applied to as-w elded joints in
order to elim inate casting defects in the gauge section. The friction stir too l w as inserted
in A C 4C H at the locations o f 6 and 12 m m aw ay from the w eld centre. The tool geometry,
tool travel and rotational speeds in FSP w ere the sam e as those in FSW. Furthermore, post
T6-heat treatment w as applied to FSPed joints. Hereafter, the specim ens are referred to as
as-w elded (FSPed) and post heat treated (PHTed) joints.
Procedures. A xia l fatigue tests w ere conduced on an electro-hydraulic fatigue testing
m achine at a frequency o f 10 H z and a stress ratio R = —1 (fu lly reversed loading) in
laboratory air.
R esu lts and D iscu ssion . M icrostructure. Figure 3 show s a m acroscopic v iew o f the
longitudinal section near the w eld zone in an as-w elded joint. It can be seen that both
materials are sufficiently stirred in the w eld zone, w here A C 4C H on the RS m oves to the
A S near the upper surface, w hile A 6061 on the A S m oves to the RS near the low er
surface. The m agnified v iew s o f the regions A ~ D in Fig. 3 are revealed in Fig. 4. In
A C 4C H near the w eld centre (Fig. 4a), dendrite structure com pletely disappears and
eutectic silicon distributes uniformly. In A 6061 near the w eld centre (Fig. 4c), equiaxed
ISSN 0556-171X. Проблемыг прочности, 2008, № l 151
Y. Uematsu, Y. Tozaki, K. Tokaji, and M. Nakamura
fine grains, w h ose average size is about 8 ,«m, are seen. It is b elieved that the grain
refinem ent o f A 6061 is due to dynam ic recrystallization during w elding process [1].
Figure 4b show s the region B w hich is the boundary betw een A C 4C H and A 6061. The
boundary line betw een both materials is distinctly v isib le, indicating that FSW is a solid
state process. In the region D (Fig. 4d), both materials are arranged in alternative layers
due to stirring under solid state.
Fig. 3. Macroscopic appearance in cross section o f as-welded joint.
Fig. 4. Microstructures o f as-welded joint: (a), (b), (c) magnified views o f region A, B, C , and
(d) region D in Fig. 3, respectively.
M acroscopic appearance in the cross section o f an FSPed join t is show n in Fig. 5, in
w hich the dotted lines represent the locations o f the centre o f friction stir tool during FSP.
Both materials are stirred more severely in the v icin ity o f the w eld centre o f the FSPed
joint. The microstructure o f FSPed A C4C H area is similar to that o f the region A in Fig. 3
(Fig. 4a). In the PHTed joint, it w as found that remarkable grain growth took p lace near
the w eld centre in A 6061 [1], w hereas there w as no or little influence on the m icro
structure in AC4CH.
Fig. 5. Macroscopic appearance in cross section o f FSPed joint.
H ardness Profile. The Vickers hardness profiles are show n in Fig. 6. The as-w elded
jo in t experiences softening inside the w eld zone, w hich m ay be attributed to the
dissolution o f precipitates due to temperature rise during FSW process. The hardness
m inim a are located on the both sides about 7 m m aw ay from the w eld centre, as show n by
arrow A in Fig. 6. The distance betw een the hardness m inim a coincides w ith the
diameter o f FSW to o l’s shoulder, indicating that remarkable softening took place along
the trace route o f FSW to o l’s shoulder edge. Such hardness m inim a are also recognized in
A 6061-T 6 FSW joints [1]. The softening area expands to A C 4C H side in the FSPed joint.
The hardness m inim a are observed as show n by arrow B in the figure, w hich correspond
to the locations o f to o l’s shoulder edge during FSW and FSP. The PHTed join t exhibits
nearly the sam e hardness value as the parent metals.
152 ISSN 0556-171X. npo6n.eMH npounocmu, 2008, N 1
Fatigue Behavior o f Dissimilar Friction Stir Welds
Fig. 6. Hardness profiles.
Tensile Strength . The average tensile strength, o b , o f three as-w elded jo in ts was
198 M Pa, w hich w as low er than those o f the parent m etals. It w as found that all joints
fractured on A 6061 side w here the hardness w as minimal.
F atigue Strength. Figure 7 represents the S — N diagram. The fatigue strength o f
the as-w elded jo in t is similar to that o f the parent m etal, AC4C H . It should be noted that
the fatigue fracture took place on A C 4C H side and the location o f fracture w as different
from tensile fracture. SEM micrograph o f fracture surface near crack initiation site o f an
as-w elded joint is revealed in Fig. 8a. Casting defect is recognized at the crack initiation
site, thus resulting in the similar fatigue strength to the parent metal, A C4C H . On the
other hand, the FSPed jo int show s nearly the sam e fatigue strength as the parent metal,
A C 4C H , in h igh stress region, but considerably higher fatigue limit. Figure 8b represents
SEM micrograph o f fracture surface near crack initiation site o f an FSPed joint, where
casting defect is not seen. This indicates that casting defects were elim inated by FSP,
w hich led to the im provem ent o f fatigue limit. Fatigue fracture o f the FSPed joints took
place at the locations o f the hardness m inim a, arrow B in Fig. 6. It is believed , therefore,
the fatigue strength in h igh stress region w as not im proved due to the softening in the
w eld zone. The fatigue strength o f the PHTed jo in t is nearly the sam e as that o f the parent
m etal, A 6061 , due to the recovery o f hardness by post heat treatment. H ow ever, fatigue
fracture still occurred along the trace route o f FSW to o l’s shoulder edges show n by arrow
B in Fig. 6.
- ....................................... . AC4CH--A6061 :
- O as-welded -
- im □ FSPed :
’ OD A A PHTed '
O Ü& ■
- . □ -
: * o A ► :
j t t -• ■—► -
’ Parent metal
- AC4CH-T6
- ■ A6061-T6
•O
200
150
50
10 10 10 10 10
Number of cycles to failure N f
Fig. 7. S — N diagram.
ISSN 0556-171X. npoôneMbi npoHHocmu, 2008, № 1 153
Y. Uematsu, Y. Tozaki, K. Tokaji, and M. Nakamura
Fig. 8. SEM micrographs showing crack initiation site: (a) as-welded (a = 160 MPa), (b) FSPed
(a = 160 MPa).
C on clusions. Fully reversed axial fatigue tests were conducted using friction stir
w elded dissimilar joints betw een cast aluminum alloy, A C4C H -T6, and wrought aluminum
alloy, A 6061-T 6. The dissim ilar joints show ed nearly the sam e fatigue strength as the
parent m etal, A C4C H , because cracks were initiated from casting defects. B y the
application o f both friction stir process and post heat treatment, the fatigue strength o f
dissim ilar jo ints w as successfu lly im proved up to that o f the parent m etal, A 6061.
1. Y. Uematsu, K. Tokaji, Y. Tozaki, and H. Shibata, Proc. o f the 16th European Conference of
Fracture (ECF 16) (2006).
2. M. A. Sutton, B. Yang, A. P. Reynolds, and T. Taylor, Mater. Sci. Eng., A323, 160 (2002).
3. A. Steuwer, M. J. Peel, and P. J. Withers, Mater. Sci. Eng., A441, 187 (2006).
Received 28. 06. 2007
154 ISSN 0556-171X. npoôneMbi npoHHocmu, 2008, № 1
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