ma e ials
A icle
Analysis o De o ma ion Beha iou and Residual
S ess in Ro a y Swaged Cu/Al Clad Composi e Wi es
Lenka Kunˇcická1, Adéla Macháˇcko á2, Ludmila K á ká2and Radim Kocich 2,*
1Ins i u e o Physics o Ma e ials, Academy o Sciences o he Czech Republic, Žižko a 22,
61600 B no, Czech Republic; [email p o ec ed]
2VŠB–Technical Uni e si y o Os a a, 17. lis opadu 15, 70833 Os a a, Czech Republic;
[email p o ec ed] (A.M.); [email p o ec ed] (L.K.)
*Co espondence: [email p o ec ed]; Tel.: +420-596-99-4455
Recei ed: 13 Sep embe 2019; Accep ed: 18 Oc obe 2019; Published: 23 Oc obe 2019


Abs ac :
Bo h coppe and aluminum a e widely applicable h oughou a a ie y o indus ial and
comme cial b anches, howe e , joining hem in a composi e p o ides he possibili y o combining
all hei ad an ageous p ope ies in one ma e ial. This s udy in es iga es uniquely sequenced
coppe –aluminum clad composi e wi es, ab ica ed ia o a y swaging echnology. The composi es
we e p ocessed a 20
◦
C and 250
◦
C o a diame e o 5 mm. S uc u al obse a ions and he
de e mina ion o esidual s ess wi hin bo h elemen s o he swaged wi es we e pe o med ia
elec on mic oscopy; he expe imen al esul s we e co ela ed wi h nume ical p edic ions. As shown
in he esul s, bo h he applied swaging o ce and empe a u e a ec ed he plas ic low, which had
a di ec in luence on esidual s ess and ex u e de elopmen ; he Al
shea h
elemen s exhibi ed ideal
olling ex u es, whe eas he Cu
wi es
elemen s ea u ed ideal shea ex u e o ien a ion. The g ains
wi hin bo h he Al
shea h
elemen s o he 5 mm composi e wi e we e e ined down o sub-mic on size.
S uc u al es o a ion also had a posi i e in luence on esidual s ess.
Keywo ds: clad composi e; o a y swaging; ini e elemen analysis; subs uc u e; esidual s ess
1. In oduc ion
Laye ed composi es, also e e ed o as clad composi es o hyb id ma e ials, a e inno a i e
ma e ials consis ing o wo o mo e me al bonds a mu ual in e aces. Gi en hei abili y o
simul aneously achie e ad an ageous mechanical and physical (e.g., he mal and elec ic.) p ope ies,
which is challenging o single-phase ma e ials, an e e -inc easing numbe o comme cial and indus ial
b anches a e gaining an in e es in composi es. They a e especially a ou ed o applica ions in which
con adic o y ma e ial p ope ies a e equi ed [
1
,
2
]. The applica ion o clad composi es makes i
possible o combine di e en p ope ies (e.g., co osion and wea esis ance, he mal and elec ic
esis i i y, magne ic p ope ies, and acous ic dumping and ene gy abso p ion.) on he inne and
ou e egions o he indi idual inal p oduc . Clad composi es a e ypically used in he ae ospace [3],
au omo i e [
4
], and ma ine indus ies [
5
], as well as in he mal enginee ing [
6
], medicine [
7
], and
elec o echnics—mul i-laye ed ma e ials in he o m o laye ed shee s and clad wi es o ods a e
p omising o ene gy ans e [8].
Composi es a e ypically bi-me allic ma e ials, howe e , mul i-me allic ma e ials and sys ems
combining me als wi h o he compounds ha e also been s udied. A wide spec um o mul i-componen
ma e ials ha e been designed and esea ched [
9
,
10
]. The p ima y esea ch aim has been o op imize
composi e p oduc ion, wi h ega d o he achie emen o ad an ageous p ope ies. Ne e heless,
economy o p oduc ion should also be conside ed, such as educing he weigh o ehicles in he
au omo i e indus y, ia applica ion o Mg-based alloys. Despi e being mo e p omising han, e.g.,
Ma e ials 2019,12, 3462; doi:10.3390/ma12213462 www.mdpi.com/jou nal/ma e ials
Ma e ials 2019,12, 3462 2 o 13
Al-based alloys, Mg-based alloys ha e se e al majo d awbacks, such as hei ela i ely low mechanical
p ope ies, low o mabili y, and low co osion esis ance, demons a ed by Mg’s endency o o m
non-p o ec i e su ace oxide laye s. Based on he esul s achie ed by he coa ing/cladding o he
su aces o Mg-based alloys wi h mo e p o ec i e ma e ials, such as aluminum o s ainless s eel, he
p oduc ion o a ious clad/laye ed composi es can be conside ed an e ec i e means o imp o ing he
beha iou o ma e ials in, bu no limi ed o, co osi e en i onmen s [
11
,
12
]. Ano he example is he
e o o educe he weigh and enhance he p ope ies o coppe componen s in elec o echnics by
adding aluminum. Recen ly, Jin e al. [
13
] p oduced Al/Cu bime al ubes ia he ube spinning p ocess,
in o de o pe o m ho ough esea ch on op imized o ming pa ame e s, while Kim and Hong [
14
]
p oduced a olled Cu/Al/Cu composi e shee o imp o e he mechanical p ope ies o he indi idual
olled Cu and Al — hey epo ed ha he ac u e s ain inc eased mo e han 25% compa ed o he
indi idual me als.
Besides selec ion o indi idual ma e ials, selec ion o sui able p oduc ion echnologies and hei
op imiza ion has ecen ly been a p ima y esea ch end. Among he widely used manu ac u ing
echnologies a e p ocesses based on welding, e.g., explosion welding [
15
–
17
], o di usion welding [
18
].
Howe e , such p ocesses ha e ce ain disad an ages, no ably he de elopmen o a hea -a ec ed zone,
ea u ing signi ican ly di e en p ope ies and a di e en s uc u e, which can nega i ely in luence
he pe o mance o he inal composi e. Fo example, Yu e .al [
19
] success ully used unde wa e
explosi e cladding o ab ica e a Cu/Al cladded ube, howe e hey also ound locally de eloped
CuAl
2
in e me allics. These d awbacks limi he possible usage o he composi es o hin and ine
componen s. Ne e heless, al e na i e means o composi e p oduc ion, ia con en ional as well as
noncon en ional me hods o se e e plas ic de o ma ion (SPD), ha e been de eloped [20,21].
Rega dless he selec ed o ming p ocess, manu ac u ing echnology is always selec ed wi h he
aim o ensu ing he highes possible quali y o mu ual bonding be ween he indi idual componen s.
When o med unde cold condi ions, clad composi es a e p one o local debonding a he in e aces. On
he o he hand, when o med unde ho condi ions, he ele a ed empe a u e can impa he o ma ion
and de elopmen o in e me allic laye s and a ec he quali y (s eng h) o he mu ual bonding o
indi idual laye s [
22
]. Fo hese easons, he ideal p ocessing empe a u e, o op imized hea ea men ,
is ypically sea ched o .
D awing has been one o he me hods used o ab ica ion o composi es [
23
], howe e , i has
se e al d awbacks, which make his me hod unsui able o clad composi e p oduc ion. Mo e sui able
echnology o composi e p oduc ion a e he widely used di ec and indi ec ex usions; he s udy by
Lee a al. [
24
] documen s he ab ica ion o a Ti/Cu composi e ia ho indi ec ex usion, pe o med
in a acuum o an ine a mosphe e, in o de o p e en he oxida ion o mu ual in e aces. O he
popula con en ional echnologies o laye ed composi e p oduc ion a e olling and olling-based
me hods [
25
–
29
]. Al hough olling is ypically pe o med in ho condi ions, combina ions o cold
olling wi h subsequen hea ea men ha e also been esea ched.
The main ad an age o non-con en ional SPD me hods is hei posi i e e ec on he s uc u es o
he p ocessed ma e ials—me hods like high p essu e o sion (HPT) [
30
,
31
], Equal channel angula
p essing (ECAP) and i s modi ica ions [
32
–
36
], o ic ion s i -based me hods [
37
,
38
], impa o ma ion
o ul a- ine g ains by imposing se e e shea s ain, wi hou he need o be p ocessed unde ho
empe a u es. Ro a y swaging (RS) and simila in ensi e plas ic de o ma ion me hods, such as he
accumula i e swaging and bundling (ASB) used by Eschke e al. [
39
] o ab ica e a Ti/Al composi e, a e
also p omising o he ab ica ion o clad composi es. A p ima y ad an age o RS is he ela i ely easy
p oduc ion o axi-symme ical composi es o unlimi ed leng hs, ea u ing ine g ains and enhanced
p ope ies [
40
]. Ne e heless, designing an op imum combina ion o componen me als and hei
sequencing, in o de o minimize inhomogenei ies in hei inal p ope ies, is challenging [
41
]. Also,
esidual s ess can de elop du ing de o ma ion p ocessing, as a esul o a ious in luencing ac o s,
such as non-uni o m hea ing/cooling, which ypically occu s unde cold condi ions, o is caused by he
inhomogeneous dis ibu ion o he imposed s ain [42].
Ma e ials 2019,12, 3462 3 o 13
Fo hese easons, his s udy ocused on a nume ical and expe imen al e alua ion o he
p esen ed Cu/Al clad composi e, e alua ing mechanical beha iou , s ess–s ain condi ions, and
ex u e de elopmen .
2. Ma e ials and Me hods
The ini ial ma e ials used o he ab ica ion o he clad composi e we e comme cially pu e (CP)
Cu (Cu wi h 0.002% O, 0.015% P, and 0.002% Zn), and elec o-conduc i e CP Al (Al wi h 0.20% Si,
0.25% Fe, and 0.05% Cu). The ini ial ou e diame e o he Al bille was 30 mm, and he diame e s o
he inse ed Cu wi es we e 3 mm each. The Al/Cu olume a io wi hin he clad composi e was 81:19.
The 5 mm Al/Cu clad composi e wi es we e manu ac u ed ia o a y swaging (RS). The basis o
he ab ica ion echnology is schema ically depic ed in Figu e 1a, in which he o a y swaging dies and
wo kpiece can be seen. RS was ca ied ou a a oom empe a u e o app oxima ely 20
◦
C (composi e
20C), and, a an ele a ed empe a u e o 250
◦
C (composi e 250C), hea ing was pe o med by induc ion,
igh be o e he inpu o he composi e in o he swaging head. The composi es we e swaged down
o 5 mm in mul iple swaging passes. The indi idual and o al educ ion a ios depic ed in Table 1
we e calcula ed using he
ϕ
=ln (S
0
/S
n
) ela ion, whe e S
0
and S
n
we e he ini ial and inal composi e
c oss-sec ions, espec i ely.
Ma e ials 2019, 12, x FOR PEER REVIEW 3 o 13
2. Ma e ials and Me hods
The ini ial ma e ials used o he ab ica ion o he clad composi e we e comme cially pu e (CP)
Cu (Cu wi h 0.002% O, 0.015% P, and 0.002% Zn), and elec o‐conduc i e CP Al (Al wi h 0.20% Si,
0.25% Fe, and 0.05% Cu). The ini ial ou e diame e o he Al bille was 30 mm, and he diame e s o
he inse ed Cu wi es we e 3 mm each. The Al/Cu olume a io wi hin he clad composi e was 81:19.
The 5 mm Al/Cu clad composi e wi es we e manu ac u ed ia o a y swaging (RS). The basis o
he ab ica ion echnology is schema ically depic ed in Figu e 1a, in which he o a y swaging dies
and wo kpiece can be seen. RS was ca ied ou a a oom empe a u e o app oxima ely 20 °C
(composi e 20C), and, a an ele a ed empe a u e o 250 °C (composi e 250C), hea ing was pe o med
by induc ion, igh be o e he inpu o he composi e in o he swaging head. The composi es we e
swaged down o 5 mm in mul iple swaging passes. The indi idual and o al educ ion a ios
depic ed in Table 1 we e calcula ed using he φ = ln (S0/Sn) ela ion, whe e S0 and Sn we e he ini ial
and inal composi e c oss‐sec ions, espec i ely.
(a) (b)
(c)
Figu e 1. Schema ic depic ion o o a y swaging se up o Al/Cu composi e (a); c oss‐sec ional cu o 5
mm 20C swaged composi e, wi h loca ions o s uc u e analyses a app oxima ely mid‐ adius o
bo h componen s, ma ked wi h “x”; (b) s ess–s ain cu es o indi idual me als used o nume ical
p edic ion (c).
Table 1. Swaging educ ions in indi idual passes o bo h 20C and 250C composi es.
Pass No. 1 2 3 4 5 6
Swaging Deg ee φ 0.36 0.81 1.38 2.20 2.77 3.58
The analyses o he swaged samples we e p ima ily ocused on he in luence o p ocessing
empe a u e on esidual s ess and ex u e de elopmen . Tho ough obse a ions we e ca ied ou
ia scanning elec on mic oscopy (SEM) and elec on backsca e ed di ac ion (EBSD). On he
c oss‐sec ional cu o he 5 mm 20C swaged composi e, he loca ions in which subsequen s uc u e
analyses we e aken a e ma ked wi h “x”, as depic ed in Figu e 1b. The ans e sal cu samples we e
mechanically g ound on SiC pape s and subsequen ly elec oly ically polished. The EBSD analyses
we e pe o med wi h a scan s ep o 0.25 µm, using a Tescan Ly a 3 equipmen (TESCAN B no s. .o,
B no, Czech Republic) wi h a No dlysNano EBSD de ec o (Ox o d Ins umen s,
Figu e 1.
Schema ic depic ion o o a y swaging se up o Al/Cu composi e (
a
); c oss-sec ional cu o
5 mm 20Cswaged composi e, wi h loca ions o s uc u e analyses a app oxima ely mid- adius o
bo h componen s, ma ked wi h “x”; (
b
) s ess–s ain cu es o indi idual me als used o nume ical
p edic ion (c).
Table 1. Swaging educ ions in indi idual passes o bo h 20Cand 250Ccomposi es.
Pass No. 1 2 3 4 5 6
Swaging Deg ee ϕ0.36 0.81 1.38 2.20 2.77 3.58
The analyses o he swaged samples we e p ima ily ocused on he in luence o p ocessing
empe a u e on esidual s ess and ex u e de elopmen . Tho ough obse a ions we e ca ied
Ma e ials 2019,12, 3462 4 o 13
ou ia scanning elec on mic oscopy (SEM) and elec on backsca e ed di ac ion (EBSD). On he
c oss-sec ional cu o he 5 mm 20C swaged composi e, he loca ions in which subsequen s uc u e
analyses we e aken a e ma ked wi h “x”, as depic ed in Figu e 1b. The ans e sal cu samples we e
mechanically g ound on SiC pape s and subsequen ly elec oly ically polished. The EBSD analyses
we e pe o med wi h a scan s ep o 0.25
µ
m, using a Tescan Ly a 3 equipmen (TESCAN B no s. .o,
B no, Czech Republic) wi h a No dlysNano EBSD de ec o (Ox o d Ins umen s, Abingdon-on-Thames,
UK). The scans we e e alua ed using he ATEX [
43
] so wa e (Win10 e sion). Residual s ess was
e alua ed ia analyses o in e nal g ain miso ien a ion on a scale o 0
◦
o 15
◦
. Tex u e was e alua ed
wi h a maximum 15◦de ia ion om ideal o ien a ion.
The expe imen was supplemen ed wi h a nume ical p edic ion ocused on he cha ac e iza ion
o de o ma ion beha iou and s ess-s a e, and he de e mina ion o swaging o ces du ing he i s
swaging pass. The nume ical analysis was pe o med wi h he use o FORGE comme cial so wa e
(NxT e sion). As seen in Figu e 1a, he ini ial assembly used o he nume ical p edic ion o cold
swaging o he composi e consis ed o ou swaging dies, he wo kpiece, and a clamp ba o eed he
wo kpiece in o he swaging head. The wo kpiece was pushed o wa d o he head a e each s oke
—each ime he dies we e in he open posi ion. All he dies pe o med a simul aneous oscilla ion in
he adial di ec ion, and a o a ion a ound he swaging axis. The en i e assembly was meshed wi h
ini e e ahed on elemen s; he Al
shea h
(diame e o 30 mm and leng h o 100 mm) mesh consis ed
o 284 125 nodes, and each o he Cu
wi es
was meshed wi h 12,760 nodes. Gi en he high numbe o
Alshea h/Cuwi e in e aces, aniso opic meshing was applied.
Swaging was ca ied ou a oom empe a u e. The ini ial empe a u e o he wo kpiece and
dies was se a 20
◦
C. F ic ion be ween he dies and wo kpiece was de e mined by he Coulomb law,
wi h a ic ion coe icien o
µ
=0.1. Ma e ial beha iou was de ined based on he s ess–s ain cu es
acqui ed ia ensile es ing o he in es iga ed ma e ials (Figu e 1c). The ensile es da a we e inpu o
he so wa e da abase and, subsequen ly, he cons i u i e model was c ea ed. Ma e ial beha iou was
inally cha ac e ized by an elas ic– iscoplas ic model, de e mined ia he simpli ied Haensel–Spi el
equa ion de ined as Equa ion (1):
σ=Aexp(m1T)εm2expm4
ε.
εm3(1)
whe e
ε
is he s ain,
.
ε
is he s ain a e, T is he empe a u e and A, m
1
, m
2
, m
3
, and m
4
a e eg ession
coe icien s. The supplemen a y he mo-physical pa ame e s ensuing om he model a e speci ied in
Table 2.
Table 2. The mo-physical pa ame e s o in es iga ed ma e ial used o simula ion.
P ope y Uni Al Cu
Poisson Coe icien - 0.3 0.3
Densi y (g.cm−3)2.7 8.9
Speci ic Hea (J.kg−1.K−1)1230 398
The mal Conduc i i y (W/(m.K)) 204 386
Among he p edic ed pa ame e s we e he adial swaging o ces, which we e measu ed
dynamically du ing he expe imen al RS, using he KOMAFU S600 sys em, o dynamic de ec ion
o swaging o ces wi h an in eg a ed dynamic measu emen o empe a u e [
44
,
45
]. De e mina ion
o swaging o ces no only indi ec ly poin s o he occu ence o s eng hening/so ening p ocesses
wi hin he swaged piece, bu also p o ides he possibili y o e i ying he pe o med simula ion,
which is use ul in p e en ing possible die b eakage and imp o es he sa e y le el o he whole
p oduc ion p ocess.
Ma e ials 2019,12, 3462 5 o 13
3. Resul s
3.1. De o ma ion Beha iou
Nume ical analysis o he i s swaging educ ion o he Al/Cu composi e was pe o med in o de
o de e mine possible di e ences in he de o ma ion beha iou s o bo h me al elemen s. As seen in
Figu e 2a, he axial plas ic low o he Al
shea h
was al eady signi ican du ing he i s swaging pass,
whe eas he plas ic low o he Cu
wi es
was no as subs an ial (simila beha iou has been documen ed
be o e, o an Al/Cu clad composi e wi h a di e en s acking sequence [
45
]). This phenomenon can
p ima ily be a ibu ed o wo ac o s. The i s is ela ed o he o al amoun and dis ibu ion o he
imposed s ain. As e iden om Figu e 2a and he axial longi udinal, cu h ough he composi e
depic ed in Figu e 2b, he maximum imposed s ain was localized in he (sub) su ace egion o
he composi e, i.e., wi hin he Al
shea h
. Howe e , he maximum alues o he imposed s ain, a
app oxima ely 0.6, we e also de ec ed a he mu ual Alshea h/Cuwi es in e ace.
Ma e ials 2019, 12, x FOR PEER REVIEW 5 o 13
dis ibu ion o he imposed s ain. As e iden om Figu e 2a and he axial longi udinal, cu h ough
he composi e depic ed in Figu e 2b, he maximum imposed s ain was localized in he (sub) su ace
egion o he composi e, i.e., wi hin he Alshea h. Howe e , he maximum alues o he imposed s ain,
a app oxima ely 0.6, we e also de ec ed a he mu ual Alshea h/Cuwi es in e ace.
The second ac o a ec ing plas ic low is ela ed o p ocessing empe a u e. Despi e he ac
ha RS was pe o med a oom empe a u e, empe a u e inc eased apidly du ing swaging, due o
he de elopmen o de o ma ion hea gene a ed p ima ily by he mo emen o a oms, gene a ion o
la ice dis o ions, and nuclea ion o s uc u al de ec s [46]. Figu e 3a shows ha he maximum
empe a u e o he swaged piece inc eased by 70% on inpu o he swaging dies’ educ ion zone.
Simila o imposed s ain, he empe a u e exhibi ed g adien dis ibu ion om he swaged piece
su ace owa ds i s axis. Howe e , as documen ed by Figu e 3b, he empe a u e g adien , caused by
he e ec o de o ma ion hea , was no linea h oughou he c oss‐sec ion o he composi e, due o
he di e en physical p ope ies o bo h he me al elemen s; he empe a u e in he axial composi e
egion was highe o he Alshea h han o he Cuwi es. Howe e , he empe a u e ield exhibi ed a
endency o homogenize du ing subsequen swaging.
(a) (b)
Figu e 2. Scala dis ibu ion o e ec i e imposed s ain (a); e ec i e s ain along axial longi udinal
cu (b).
(a) (b)
Figu e 3. Dis ibu ion o empe a u e h oughou 20C swaged composi e: su ace (a); axial
longi udinal cu (b).
Due o he e ec o he a o emen ioned phenomena, and he a he complex mu ual in luence o
he axial and angen ial swaging o ce componen s [8], he plas ic low was no only di e en o
bo h composi e elemen s, bu also changed i s cha ac e du ing he swaging pass. A he beginning
o he swaging pass, a he momen he dies came in o he con ac wi h he ma e ial, he ma e ial
expe ienced a solely angen ial low (Figu e 4a). The angen ial plas ic low componen hen
domina ed he axial low componen , as he dies came in o ull con ac wi h he ma e ial (Figu e 4b).
The en i e closu e o he swaging head hen caused he axial plas ic low o domina e he angen ial
low componen (Figu e 4c). The dominan axial plas ic low o he Alshea h supp essed he axial
plas ic low o he Cuwi es, as seen in Figu e 4d. This phenomenon indica es ha he plas ic low o he
Alshea h swi ched owa d he unswaged pa o he piece, due o he mu ual in luence o he a ying
Figu e 2.
Scala dis ibu ion o e ec i e imposed s ain (
a
); e ec i e s ain along axial longi udinal
cu (b).
The second ac o a ec ing plas ic low is ela ed o p ocessing empe a u e. Despi e he ac
ha RS was pe o med a oom empe a u e, empe a u e inc eased apidly du ing swaging, due o
he de elopmen o de o ma ion hea gene a ed p ima ily by he mo emen o a oms, gene a ion
o la ice dis o ions, and nuclea ion o s uc u al de ec s [
46
]. Figu e 3a shows ha he maximum
empe a u e o he swaged piece inc eased by 70% on inpu o he swaging dies’ educ ion zone.
Simila o imposed s ain, he empe a u e exhibi ed g adien dis ibu ion om he swaged piece
su ace owa ds i s axis. Howe e , as documen ed by Figu e 3b, he empe a u e g adien , caused by
he e ec o de o ma ion hea , was no linea h oughou he c oss-sec ion o he composi e, due o he
di e en physical p ope ies o bo h he me al elemen s; he empe a u e in he axial composi e egion
was highe o he Al
shea h
han o he Cu
wi es
. Howe e , he empe a u e ield exhibi ed a endency
o homogenize du ing subsequen swaging.
Ma e ials 2019, 12, x FOR PEER REVIEW 5 o 13
dis ibu ion o he imposed s ain. As e iden om Figu e 2a and he axial longi udinal, cu h ough
he composi e depic ed in Figu e 2b, he maximum imposed s ain was localized in he (sub) su ace
egion o he composi e, i.e., wi hin he Alshea h. Howe e , he maximum alues o he imposed s ain,
a app oxima ely 0.6, we e also de ec ed a he mu ual Alshea h/Cuwi es in e ace.
The second ac o a ec ing plas ic low is ela ed o p ocessing empe a u e. Despi e he ac
ha RS was pe o med a oom empe a u e, empe a u e inc eased apidly du ing swaging, due o
he de elopmen o de o ma ion hea gene a ed p ima ily by he mo emen o a oms, gene a ion o
la ice dis o ions, and nuclea ion o s uc u al de ec s [46]. Figu e 3a shows ha he maximum
empe a u e o he swaged piece inc eased by 70% on inpu o he swaging dies’ educ ion zone.
Simila o imposed s ain, he empe a u e exhibi ed g adien dis ibu ion om he swaged piece
su ace owa ds i s axis. Howe e , as documen ed by Figu e 3b, he empe a u e g adien , caused by
he e ec o de o ma ion hea , was no linea h oughou he c oss‐sec ion o he composi e, due o
he di e en physical p ope ies o bo h he me al elemen s; he empe a u e in he axial composi e
egion was highe o he Alshea h han o he Cuwi es. Howe e , he empe a u e ield exhibi ed a
endency o homogenize du ing subsequen swaging.
(a) (b)
Figu e 2. Scala dis ibu ion o e ec i e imposed s ain (a); e ec i e s ain along axial longi udinal
cu (b).
(a) (b)
Figu e 3. Dis ibu ion o empe a u e h oughou 20C swaged composi e: su ace (a); axial
longi udinal cu (b).
Due o he e ec o he a o emen ioned phenomena, and he a he complex mu ual in luence o
he axial and angen ial swaging o ce componen s [8], he plas ic low was no only di e en o
bo h composi e elemen s, bu also changed i s cha ac e du ing he swaging pass. A he beginning
o he swaging pass, a he momen he dies came in o he con ac wi h he ma e ial, he ma e ial
expe ienced a solely angen ial low (Figu e 4a). The angen ial plas ic low componen hen
domina ed he axial low componen , as he dies came in o ull con ac wi h he ma e ial (Figu e 4b).
The en i e closu e o he swaging head hen caused he axial plas ic low o domina e he angen ial
low componen (Figu e 4c). The dominan axial plas ic low o he Alshea h supp essed he axial
plas ic low o he Cuwi es, as seen in Figu e 4d. This phenomenon indica es ha he plas ic low o he
Alshea h swi ched owa d he unswaged pa o he piece, due o he mu ual in luence o he a ying
Figu e 3.
Dis ibu ion o empe a u e h oughou 20C swaged composi e: su ace (
a
); axial longi udinal
cu (b).

Ma e ials 2019,12, 3462 6 o 13
Due o he e ec o he a o emen ioned phenomena, and he a he complex mu ual in luence o
he axial and angen ial swaging o ce componen s [
8
], he plas ic low was no only di e en o bo h
composi e elemen s, bu also changed i s cha ac e du ing he swaging pass. A he beginning o he
swaging pass, a he momen he dies came in o he con ac wi h he ma e ial, he ma e ial expe ienced
a solely angen ial low (Figu e 4a). The angen ial plas ic low componen hen domina ed he axial
low componen , as he dies came in o ull con ac wi h he ma e ial (Figu e 4b). The en i e closu e
o he swaging head hen caused he axial plas ic low o domina e he angen ial low componen
(Figu e 4c). The dominan axial plas ic low o he Al
shea h
supp essed he axial plas ic low o he
Cu
wi es
, as seen in Figu e 4d. This phenomenon indica es ha he plas ic low o he Al
shea h
swi ched
owa d he unswaged pa o he piece, due o he mu ual in luence o he a ying e ec s o bo h he
swaging o ce componen s and he geome y (conical shape) o he swaging dies educ ion zone.
Ma e ials 2019, 12, x FOR PEER REVIEW 6 o 13
e ec s o bo h he swaging o ce componen s and he geome y (conical shape) o he swaging dies
educ ion zone.
(a) (b)
(c) (d)
(e)
Figu e 4. Vec o p o iles o plas ic low o composi e 20C: dies in con ac wi h swaged‐piece (a); dies
closing and o a ing (b); dies ully a ec ing he swaged piece (c); plas ic low o Cu
wi es
(d); 20C
expe imen al composi e a e i s swaging pass (e).
The di e en de o ma ion beha iou s o bo h me al elemen s in luenced he s ess–s ain
condi ions wi hin he swaged piece, as well. Since o a y swaging p omo es mu ual bonding o he
indi idual in e aces, ia mechanical locking and di usion bonding [47], he inc emen al cha ac e
o he imposed s ain especially a ec ed he local s ess s a e. Al hough he c oss‐sec ional cu o he
swaged piece exhibi ed p e ailing comp essi e s ess, loca ions ea u ing ensile s ess we e also
p esen . Howe e , hei occu ence was p ima ily limi ed o he Al
shea h
/Cu
wi es
in e aces and
selec ed egions o he composi e su ace a ea (Figu e 5). The maximum alues o bo h he s ess
componen s anged wi hin ±50 MPa.
Figu e 4.
Vec o p o iles o plas ic low o composi e 20C: dies in con ac wi h swaged-piece (
a
);
dies closing and o a ing (
b
); dies ully a ec ing he swaged piece (
c
); plas ic low o Cu
wi es
(
d
); 20C
expe imen al composi e a e i s swaging pass (e).
Thedi e en de o ma ionbeha iou so bo hme alelemen sin luenced hes ess–s aincondi ions
wi hin he swaged piece, as well. Since o a y swaging p omo es mu ual bonding o he indi idual
in e aces, ia mechanical locking and di usion bonding [
47
], he inc emen al cha ac e o he imposed
s ain especially a ec ed he local s ess s a e. Al hough he c oss-sec ional cu o he swaged piece
exhibi ed p e ailing comp essi e s ess, loca ions ea u ing ensile s ess we e also p esen . Howe e ,
Ma e ials 2019,12, 3462 7 o 13
hei occu ence was p ima ily limi ed o he Al
shea h
/Cu
wi es
in e aces and selec ed egions o he
composi e su ace a ea (Figu e 5). The maximum alues o bo h he s ess componen s anged wi hin
±50 MPa.
Ma e ials 2019, 12, x FOR PEER REVIEW 7 o 13
Figu e 5. P edic ed dis ibu ion o in e nal s ess h oughou 20C composi e c oss‐sec ion.
3.2. Swaging Pa ame e s
The nume ically p edic ed load—swaging o ce—was subsequen ly e i ied ia dynamic
measu emen o he expe imen al swaging o ces. Mu ual compa ison o he nume ically p edic ed
and expe imen ally measu ed de elopmen o o ces du ing cold swaging exhibi s a sa is ac o y
co ela ion (Figu e 6a). Howe e , ce ain di e ences be ween he wo cu es can be obse ed. Figu e
6a shows an inc ease in o ce a app oxima ely 500 s okes (i.e., 500 hi s o he swaging dies o he
swaged piece), which can be a ibu ed o changes in he plas ic low (mos likely ela ed o he
inc easing in luence o he unswaged end [45]), which agg a a es he low o he swaged ma e ial
ou o he swaging dies, and consequen ly inc eases he low s ess (mu ual compa ison o he
p edic ed and eal composi e plas ic low can be shown using Figu es 2 and 4). Ne e heless, mos o
he di e ences be ween he wo swaging o ce de elopmen s we e ela ed o sligh a ia ions in he
inpu pa ame e s— ac o s such as emeshing, de ined he mo‐physical p ope ies o he used
ma e ials, o ibological condi ions.
The measu ing sys em no only allows assessmen o he o e all load o he machine, bu also
he indi idual moni o ing o each swaging die; he de ail in Figu e 6b shows he peak o ces o all
ou swaging dies du ing se e al indi idual s okes. The measu ed indi idual o ces documen
homogeneous load, i.e., he homogenei y o he imposed s ain, h oughou bo h he composi e
leng h and c oss‐sec ion.
(a) (b)
Figu e 6. Compa ison o nume ically p edic ed and dynamically measu ed swaging o ce
de elopmen s (a); dynamically measu ed swaging o ces o 20C composi e (b).
3.3. Residual S ess and G ain Size
Cha ac e iza ion o esidual s ess wi hin laye ed mul i‐me allic composi es is especially
impo an , due o he di e en p ope ies o indi idual elemen me als. The analyses we e
pe o med ia he e alua ion o in e nal g ain miso ien a ion on he EBSD scans, acqui ed in he
loca ions depic ed in Figu e 1a, on he ainbow scale om blue (0°), o ed (15°). The dis ibu ion o
he in e nal miso ien a ion poin s o he dis ibu ion o esidual s ess. As seen in Figu e 7a,b, bo h
he Alshea h elemen s ea u ed es o ed ul a‐ ine g ains (UFG), wi h a low amoun o miso ien a ion
(p e ailing blue colou ). The a e age Alshea h g ain a eas o he 20C and 250C composi es we e 0.62
and 0.39 µm2, espec i ely. On he o he hand, in e nal miso ien a ions we e obse ed wi hin he
Figu e 5. P edic ed dis ibu ion o in e nal s ess h oughou 20C composi e c oss-sec ion.
3.2. Swaging Pa ame e s
The nume ically p edic ed load—swaging o ce—was subsequen ly e i ied ia dynamic
measu emen o he expe imen al swaging o ces. Mu ual compa ison o he nume ically p edic ed and
expe imen ally measu ed de elopmen o o ces du ing cold swaging exhibi s a sa is ac o y co ela ion
(Figu e 6a). Howe e , ce ain di e ences be ween he wo cu es can be obse ed. Figu e 6a shows an
inc ease in o ce a app oxima ely 500 s okes (i.e., 500 hi s o he swaging dies o he swaged piece),
which can be a ibu ed o changes in he plas ic low (mos likely ela ed o he inc easing in luence o
he unswaged end [
45
]), which agg a a es he low o he swaged ma e ial ou o he swaging dies,
and consequen ly inc eases he low s ess (mu ual compa ison o he p edic ed and eal composi e
plas ic low can be shown using Figu es 2and 4). Ne e heless, mos o he di e ences be ween he
wo swaging o ce de elopmen s we e ela ed o sligh a ia ions in he inpu pa ame e s— ac o s
such as emeshing, de ined he mo-physical p ope ies o he used ma e ials, o ibological condi ions.
Ma e ials 2019, 12, x FOR PEER REVIEW 7 o 13
Figu e 5. P edic ed dis ibu ion o in e nal s ess h oughou 20C composi e c oss‐sec ion.
3.2. Swaging Pa ame e s
The nume ically p edic ed load—swaging o ce—was subsequen ly e i ied ia dynamic
measu emen o he expe imen al swaging o ces. Mu ual compa ison o he nume ically p edic ed
and expe imen ally measu ed de elopmen o o ces du ing cold swaging exhibi s a sa is ac o y
co ela ion (Figu e 6a). Howe e , ce ain di e ences be ween he wo cu es can be obse ed. Figu e
6a shows an inc ease in o ce a app oxima ely 500 s okes (i.e., 500 hi s o he swaging dies o he
swaged piece), which can be a ibu ed o changes in he plas ic low (mos likely ela ed o he
inc easing in luence o he unswaged end [45]), which agg a a es he low o he swaged ma e ial
ou o he swaging dies, and consequen ly inc eases he low s ess (mu ual compa ison o he
p edic ed and eal composi e plas ic low can be shown using Figu es 2 and 4). Ne e heless, mos o
he di e ences be ween he wo swaging o ce de elopmen s we e ela ed o sligh a ia ions in he
inpu pa ame e s— ac o s such as emeshing, de ined he mo‐physical p ope ies o he used
ma e ials, o ibological condi ions.
The measu ing sys em no only allows assessmen o he o e all load o he machine, bu also
he indi idual moni o ing o each swaging die; he de ail in Figu e 6b shows he peak o ces o all
ou swaging dies du ing se e al indi idual s okes. The measu ed indi idual o ces documen
homogeneous load, i.e., he homogenei y o he imposed s ain, h oughou bo h he composi e
leng h and c oss‐sec ion.
(a) (b)
Figu e 6. Compa ison o nume ically p edic ed and dynamically measu ed swaging o ce
de elopmen s (a); dynamically measu ed swaging o ces o 20C composi e (b).
3.3. Residual S ess and G ain Size
Cha ac e iza ion o esidual s ess wi hin laye ed mul i‐me allic composi es is especially
impo an , due o he di e en p ope ies o indi idual elemen me als. The analyses we e
pe o med ia he e alua ion o in e nal g ain miso ien a ion on he EBSD scans, acqui ed in he
loca ions depic ed in Figu e 1a, on he ainbow scale om blue (0°), o ed (15°). The dis ibu ion o
he in e nal miso ien a ion poin s o he dis ibu ion o esidual s ess. As seen in Figu e 7a,b, bo h
he Alshea h elemen s ea u ed es o ed ul a‐ ine g ains (UFG), wi h a low amoun o miso ien a ion
(p e ailing blue colou ). The a e age Alshea h g ain a eas o he 20C and 250C composi es we e 0.62
and 0.39 µm2, espec i ely. On he o he hand, in e nal miso ien a ions we e obse ed wi hin he
Figu e 6.
Compa isono nume ically p edic edanddynamicallymeasu edswaging o cede elopmen s
(a); dynamically measu ed swaging o ces o 20C composi e (b).
The measu ing sys em no only allows assessmen o he o e all load o he machine, bu also
he indi idual moni o ing o each swaging die; he de ail in Figu e 6b shows he peak o ces o
all ou swaging dies du ing se e al indi idual s okes. The measu ed indi idual o ces documen
homogeneous load, i.e., he homogenei y o he imposed s ain, h oughou bo h he composi e leng h
and c oss-sec ion.
3.3. Residual S ess and G ain Size
Cha ac e iza ion o esidual s ess wi hin laye ed mul i-me allic composi es is especially impo an ,
due o he di e en p ope ies o indi idual elemen me als. The analyses we e pe o med ia he
Ma e ials 2019,12, 3462 8 o 13
e alua ion o in e nal g ain miso ien a ion on he EBSD scans, acqui ed in he loca ions depic ed
in Figu e 1a, on he ainbow scale om blue (0
◦
), o ed (15
◦
). The dis ibu ion o he in e nal
miso ien a ion poin s o he dis ibu ion o esidual s ess. As seen in Figu e 7a,b, bo h he Al
shea h
elemen s ea u ed es o ed ul a- ine g ains (UFG), wi h a low amoun o miso ien a ion (p e ailing
blue colou ). The a e age Al
shea h
g ain a eas o he 20C and 250C composi es we e 0.62 and 0.39
µ
m
2
,
espec i ely. On he o he hand, in e nal miso ien a ions we e obse ed wi hin he Cu
wi es
o bo h
composi es (Figu e 7c,d). The g ain size analyses o Cu
wi es
e ealed he Cu g ains o be la ge han he
Al g ains; he a e age g ain a eas we e 2.1 µm2 o composi e 20C, and 2.9 µm2 o composi e 250C.
Ma e ials 2019, 12, x FOR PEER REVIEW 8 o 13
Cu
wi es
o bo h composi es (Figu e 7c,d). The g ain size analyses o Cu
wi es
e ealed he Cu g ains o
be la ge han he Al g ains; he a e age g ain a eas we e 2.1 µm
2
o composi e 20C, and 2.9 µm
2
o
composi e 250C.
(a) (b)
(c) (d)
Figu e 7. Maps o in e nal g ain miso ien a ion, indica ing dis ibu ion o esidual s ess o 20C
composi e: Al
shea h
(a); Cu
wi e
(b); 250C composi e—Al
shea h
(c); Cu
wi e
(d).
3.4. Tex u e
Figu e 8a–d show he (111), (100), and (110) pole igu es (PF) o he Al
shea hs
and Cu
wi es
o bo h
he 20C and 250C composi es. In he igu es, ele an dis inc i e shea [48], ec ys alliza ion and
olling [49] ideal o ien a ions a e also depic ed. As shown, he ex u es o Al
shea h
in bo h composi es
ea u e p e e en ial o ien a ions ypical o olled and ec ys allized FCC me als. The Al
shea h
o he
20C composi e exhibi ed he endency o o m he ideal Goss ex u e, he cha ac e is ic poin s o
which a e depic ed by Gs symbols in he PFs in Figu e 8a. As shown in Figu e 8b, he Al
shea h
o he
250C composi e also exhibi ed he endency o o m ideal ex u e ib es. The highes in ensi ies we e
ound o he Coppe (Cu) and Cube (Cb) o ien a ions, howe e , ideal o ien a ions we e shi ed by 10°.
The Cu
wi es
o bo h he 20C and 250C composi es ea u ed a endency o o m ideal shea ex u e
componen s. The 20C composi e Cu
wi es
ea u ed he A1 ideal shea ex u e ib e (Figu e 8c),
howe e , he (100) PF also exhibi ed a s ong peak no co esponding o any ideal o ien a ion; i was
shi ed by abou 10° om he ideal A ib e shea ex u e, and by abou 15° om he Cube and Coppe
ideal o ien a ions. Las ly, Figu e 8d documen s he e ec s o swaging on he 250C composi e Cu
wi es
.
The g ains exhibi ed a endency o o m bo h he olling/ ec ys alliza ion (Gs) and shea (A, B) ideal
ex u e o ien a ions.
Figu e 7.
Maps o in e nal g ain miso ien a ion, indica ing dis ibu ion o esidual s ess o 20C
composi e: Alshea h (a); Cuwi e (b); 250C composi e—Alshea h (c); Cuwi e (d).
3.4. Tex u e
Figu e 8a–d show he (111), (100), and (110) pole igu es (PF) o he Al
shea hs
and Cu
wi es
o bo h
he 20C and 250C composi es. In he igu es, ele an dis inc i e shea [
48
], ec ys alliza ion and
olling [
49
] ideal o ien a ions a e also depic ed. As shown, he ex u es o Al
shea h
in bo h composi es
ea u e p e e en ial o ien a ions ypical o olled and ec ys allized FCC me als. The Al
shea h
o he
20C composi e exhibi ed he endency o o m he ideal Goss ex u e, he cha ac e is ic poin s o
which a e depic ed by Gs symbols in he PFs in Figu e 8a. As shown in Figu e 8b, he Al
shea h
o
he 250C composi e also exhibi ed he endency o o m ideal ex u e ib es. The highes in ensi ies
we e ound o he Coppe (Cu) and Cube (Cb) o ien a ions, howe e , ideal o ien a ions we e shi ed
by 10
◦
. The Cu
wi es
o bo h he 20C and 250C composi es ea u ed a endency o o m ideal shea
ex u e componen s. The 20C composi e Cu
wi es
ea u ed he A1 ideal shea ex u e ib e (Figu e 8c),
howe e , he (100) PF also exhibi ed a s ong peak no co esponding o any ideal o ien a ion; i was
shi ed by abou 10
◦
om he ideal A ib e shea ex u e, and by abou 15
◦
om he Cube and Coppe
ideal o ien a ions. Las ly, Figu e 8d documen s he e ec s o swaging on he 250C composi e Cu
wi es
.
Ma e ials 2019,12, 3462 9 o 13
The g ains exhibi ed a endency o o m bo h he olling/ ec ys alliza ion (Gs) and shea (A,B) ideal
ex u e o ien a ions.
Ma e ials 2019, 12, x FOR PEER REVIEW 9 o 13
(a)
(b)
(c)
(d)
Figu e 8. Pole Figu es o Alshea h o composi e 20C (a); composi e 250C (b); Cuwi es o composi e 20C
(c); composi e 250C (d).
4. Discussion
The di e ences in he plas ic lows o bo h he me al elemen s can non‐negligibly in luence he
o e all pe o mance o he inal swaged composi e. As p e iously epo ed, ma e ial low du ing
swaging is p ima ily in luenced by he wo main swaging o ce componen s, angen ial and axial [8].
A he beginning o a swaging pass, he angen ial plas ic low componen domina es he axial one,
bu he axial low componen s a s o domina e he angen ial one du ing con inuing swaging [45].
Howe e , none o hese componen s a e equal o ze o du ing he swaging pass, as documen ed by
he p edic ed and dynamically measu ed swaging o ce de elopmen s. Figu e 6a,b show ha
swaging o ce exhibi ed a apid inc ease, ollowed by a mo e o less s eady pe iod, and a subsequen
sligh dec ease. The apid inc ease in o ce co esponded o he g adual illing o he swaging head
wi h he unswaged ma e ial, and he dec ease in he peak o ce was caused by wo main in luencing
ac o s, he i s o which was a dec ease in composi e low s ess, due o he in luence o inc eased
Figu e 8.
Pole Figu es o Al
shea h
o composi e 20C (
a
); composi e 250C (
b
); Cu
wi es
o composi e 20C
(c); composi e 250C(d).
4. Discussion
The di e ences in he plas ic lows o bo h he me al elemen s can non-negligibly in luence he
o e all pe o mance o he inal swaged composi e. As p e iously epo ed, ma e ial low du ing
swaging is p ima ily in luenced by he wo main swaging o ce componen s, angen ial and axial [
8
].
A he beginning o a swaging pass, he angen ial plas ic low componen domina es he axial one,
bu he axial low componen s a s o domina e he angen ial one du ing con inuing swaging [
45
].
Howe e , none o hese componen s a e equal o ze o du ing he swaging pass, as documen ed by he
p edic ed and dynamically measu ed swaging o ce de elopmen s. Figu e 6a,b show ha swaging
o ce exhibi ed a apid inc ease, ollowed by a mo e o less s eady pe iod, and a subsequen sligh