Ci a ion: Bilbao, Y.; T ujillo, J.J.;
Vica io, I.; A ueba ena, G.;
Hu ado, I.; Gu aya, T. X- ay
The mo-Di ac ion S udy o he
Aluminum-Based Mul icomponen
Alloy Al58Zn28Si8Mg6.Ma e ials 2022,
15, 5056. h ps://doi.o g/10.3390/
ma15145056
Academic Edi o : Lijun Zhang
Recei ed: 21 June 2022
Accep ed: 19 July 2022
Published: 20 July 2022
Publishe ’s No e: MDPI s ays neu al
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Licensee MDPI, Basel, Swi ze land.
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dis ibu ed unde he e ms and
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A ibu ion (CC BY) license (h ps://
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ma e ials
A icle
X- ay The mo-Di ac ion S udy o he Aluminum-Based
Mul icomponen Alloy Al58Zn28Si8Mg6
Yoana Bilbao 1,* , Juan JoséT ujillo 2, Iban Vica io 3, Gu u ze A ueba ena 2, Iñaki Hu ado 2
and Te esa Gu aya 1
1
Depa men o Mining and Me allu gical Enginee ing and Ma e ials Science, Facul y o Enginee ing o Bilbao,
Uni e si y o he Basque Coun y (UPV/EHU), 48013 Bilbao, Spain; [email p o ec ed]
2Mechanical and Manu ac u ing Depa men , Facul y o Enginee ing, Mond agon Unibe si a ea,
20500 A asa e/Mond agon, Spain; [email p o ec ed] (J.J.T.); [email p o ec ed] (G.A.);
[email p o ec ed] (I.H.)
3Manu ac u ing P ocesses and Ma e ials Depa men , Tecnalia, Basque Resea ch and Technology
Alliance (BRTA), 48160 De io, Spain; [email p o ec ed]
*Co espondence: [email p o ec ed]
Abs ac :
Newly designed mul icomponen ligh alloys a e gi ing ise o non-con en ional mi-
c os uc u es ha need o be ho oughly s udied be o e de e mining hei po en ial applica ions.
In his s udy, he no el Al
58
Zn
28
Si
8
Mg
6
alloy, p e iously s udied wi h CALPHAD me hods, was
cas and hea - ea ed unde se e al condi ions. An analysis o he phase e olu ion was ca ied ou
wi h in si u X- ay di ac ion suppo ed by di e en ial scanning calo ime y and elec on mic oscopy.
A o al o eigh phases we e iden i ied in he alloy in he empe a u e ange om 30 o 380
◦
C:
α
-Al,
α
’-Al, Zn, Si, Mg
2
Si, MgZn
2
, Mg
2
Zn
11
, and S Zn
13
. Se e al he mal ansi ions below 360
◦
C we e
de e mined, and he na u al p ecipi a ion o he Zn phase was con i med a e nine mon hs. The
s udy showed ha he he mal his o y can s ongly a ec he p esence o he MgZn
2
and Mg
2
Zn
11
phases. The combina ion o X- ay he mo-di ac ion wi h CALPHAD me hods, di e en ial scanning
calo ime y, and elec on mic oscopy o e ed us a sa is ac o y unde s anding o he alloy beha io a
di e en empe a u es.
Keywo ds:
ligh weigh mul icomponen alloys; X- ay he mo-di ac ion; di e en ial scanning
calo ime y; Al–Zn; Zn p ecipi a ion; Mg–Zn phases; s on ium modi ica ion
1. In oduc ion
His o ically, me allic alloys ha e been de eloped by selec ing one o wo majo com-
ponen s and adding se e al mino ones ha con e speci ic p ope ies, such as co osion
esis ance o highe mechanical p ope ies. The mul icomponen alloy concep , howe e ,
is based on he design o alloys whe e he e a e se e al main componen s ha co e he
cen al a eas o phase diag ams [1].
Ini ial de elopmen s in he ield ocused mainly on s eel-like alloys o indus ial
applica ions. They we e based on equia omic and nea -equia omic composi ions o Co,
C , Cu, Fe, Mn, o Ni, some imes adding Al, Ti, o Z , ha esul ed in single o dual
phase mic os uc u es [
2
–
7
]. Yeh e al. sugges ed ha he p e alence o solid solu ions
o e in e me allic phases could be explained by he high mixing en opy gene a ed by he
mul iple componen s in he alloy, hence he e m “high-en opy alloys” (HEAs) [
8
]. The
condi ions ha he alloys should sa is y o be conside ed HEAs may be ound in [9].
O e he pas decade, esea ch has been ex ended o o he alloy classi ica ions ha
ha e e ol ed om he o iginal HEA concep : “medium-en opy alloys” (MEAs) [
9
], “non-
equia omic HEAs”, o “mul i-phase HEAs” ha may con ain bulky seconda y phases [
10
].
In ac , he idea o in en ionally ha ing seconda y phases in his ype o alloy was i s
sugges ed by Mi acle e al. [
11
]. O he alloy amilies ha e also been explo ed, leading
Ma e ials 2022,15, 5056. h ps://doi.o g/10.3390/ma15145056 h ps://www.mdpi.com/jou nal/ma e ials
Ma e ials 2022,15, 5056 2 o 14
o e ac o y me al HEAs o high empe a u e s uc u al applica ions based on C , H ,
Mo, Nb, Ta, Ti, V, and W o ligh weigh mul icomponen alloys in he ae onau ical ield
in ol ing Al, Li, Mg, o Zn. Se e al s udies may be ound in he li e a u e as p oo o his
endency [12–17].
Among he ligh weigh mul icomponen alloys, Yang e al. explo ed he Al–Li–Mg–
(Zn, Cu, Sn) sys em, ob aining s uc u es domina ed by in e me allic compounds. The
aluminum ace-cen e ed cubic (FCC) s uc u e p edomina ed only in selec ed alloy compo-
si ions [
18
]. In ac , Sanchez e al. highligh ed he di icul y o o ming solid solu ions in
medium en opy alloys based on aluminum (65–70 a . %) wi h elemen s such as Cu, Mg, C ,
Fe, Si, Ni, Zn, o Z . The magni ude o he nega i e mixing en halpy o aluminum wi h an-
si ion me als ga e ise o in e me allic phases [
19
]. The p esence o in e me allics was also
epo ed by Tun e al. [
20
]. Only he mos ecen esea ch sugges s ha apid solidi ica ion
p ocesses may enhance single phase mic os uc u es in his ype o alloy [
21
]. Howe e ,
in a p e ious wo k by Nagase e al. on Al–Mg–Li–Ca equia omic and non-equia omic
alloys, a single solid solu ion could no be ob ained, e en wi h apid solidi ica ion [22].
Asadikiya e al. conside ed ha he applica ion o he en opy concep in aluminum
alloys may be he answe o he challenge o de eloping no el Al alloys wi h imp o ed
p ope ies [
10
]. The e o e, mul icomponen ligh weigh alloys con inue o be esea ched
o hei po en ial applica ions.
In he p esen s udy, he objec i e was o cha ac e ize he no el Al
58
Zn
28
Si
8
Mg
6
cas
alloy. I was designed o ob ain as much solid solu ion o aluminum and zinc as possible,
ein o ced wi h in e me allics based on Zn, Mg, and Si. On he one hand, zinc is highly
soluble in aluminum, enhancing he ob en ion o a solid solu ion ma ix. On he o he hand,
Mg–Zn phases a e he usual p ecipi a es in 7xx.x aluminum cas alloys, while Mg–Si phases
a e common in 3xx.x alloys. In addi ion, Al–Zn-based alloys ha e a ac ed he in e es o
esea che s beyond hei usual use as coa ings. In ac , Al–Zn cas alloys ha e po en ial
applica ions whe e ibological and damping p ope ies a e equi ed [
23
–
25
]. In e ms o
en opy, ou mul icomponen alloy would be classi ied as a mul i-phase MEA.
The app oach was explo ed by he CALPHAD (calcula ion o phase diag ams) me hod.
This echnique equi es da abases ha a e alid in composi ion anges ha may no be
ound in con en ional alloys, hus demanding u he expe imen al e i ica ion [
26
]. How-
e e , i is conside ed he mos di ec me hod o composi ional design [
27
] and has al eady
been used in he design o ligh weigh mul icomponen alloys wi h di e ing deg ees o
success [28–30].
The s udy is ocused on iden i ying and e alua ing he e ec o he empe a u e on
he phases ha a e gene a ed a di e en ini ial he mal condi ions. Di e en ial scanning
calo ime y (DSC), elec on mic oscopy, and X- ay he mo-di ac ion a e he echniques
used in his e alua ion.
X- ay
he mo-di ac ion, also known as “high empe a u e
X- ay
di ac ion” (HT-XRD), enables he in si u s udy o he solu ion and p ecipi a ion phenom-
ena in he alloys [31–33].
2. Ma e ials and Me hods
2.1. Ma e ial Manu ac u ing
Aluminum was mel ed a 750
◦
C in a esis ance u nace wi h o ced con ec ion; silicon
and zinc we e subsequen ly added. Magnesium ollowed, and once all he elemen s we e
mel ed, s on ium was added as a silicon modi ie . Aluminum, magnesium, and silicon
we e o comme cial pu i y, whe eas zinc was inco po a ed by adding a Zamak Zn4Al1Cu
alloy so ha he inal alloy composi ion con ained some esidual coppe . Samples we e
ob ained o de e mine he chemical composi ion by induc i ely coupled plasma mass
spec ome y (ICP) (Table 1).
The me al was g a i y cas in o a g aphi e mold, and samples we e ob ained ha we e
50 mm long, 22.5 mm wide, and 4 mm hick.
Ma e ials 2022,15, 5056 3 o 14
Table 1. Chemical composi ion o he alloy analyzed by ICP.
Al Zn Mg Si Cu Fe S
w . % 41.15 48.40 4.11 5.83 0.43 0.05 0.03
a . % 57.56 27.93 6.38 7.83 0.26 0.03 0.01
2.2. Selec ion o Sample The mal T ea men s and S udy Tempe a u es
In o de o selec he empe a u es o in e es , DSC es s we e pe o med on as-cas
samples (Figu e 1). A Ne zsch STA 449 Fe Jupi e calo ime e was used, and measu emen s
we e made unde a gon a mosphe e in a empe a u e ange be ween 25 and 675
◦
C wi h
a hea ing a e o 10
◦
C/min. Samples we e hen cooled down back o oom empe a u e
unde hese same condi ions.
Ma e ials 2022, 15, 5056 3 o 15
Table 1. Chemical composi ion o he alloy analyzed by ICP.
Al Zn Mg Si Cu Fe S
w . % 41.15 48.40 4.11 5.83 0.43 0.05 0.03
a . % 57.56 27.93 6.38 7.83 0.26 0.03 0.01
The me al was g a i y cas in o a g aphi e mold, and samples we e ob ained ha
we e 50 mm long, 22.5 mm wide, and 4 mm hick.
2.2. Selec ion o Sample The mal T ea men s and S udy Tempe a u es
In o de o selec he empe a u es o in e es , DSC es s we e pe o med on as-cas
samples (Figu e 1). A Ne zsch STA 449 Fe Jupi e calo ime e was used, and
measu emen s we e made unde a gon a mosphe e in a empe a u e ange be ween 25
and 675 °C wi h a hea ing a e o 10 °C/min. Samples we e hen cooled down back o
oom empe a u e unde hese same condi ions.
Figu e 1. DSC cu es o he as-cas sample. Peak empe a u es du ing hea ing we e conside ed o
he he mal ea men selec ion o he samples.
We decided o subjec he samples o se en di e en he mal condi ions o y o
sepa a e and simpli y he iden i ica ion o he di e en phases appea ing and
disappea ing du ing he hea ing p ocess (Table 2 and Figu e 2).
Table 2. Hea ea men s o each sample condi ion. The wo-s ep solu ion ea men in Q360 and
Q380 was applied o p e en any pa ial mel ing du ing one-s ep solu ion ea men a he solu ion
empe a u e.
Sample Condi ion Hea T ea men
as-cas None.
Eq280 Hea ed o 280 °C and immedia ely slowly cooled (10 °C/min) o oom empe a u e.
Eq360 Hea ed o 360 °C and immedia ely slowly cooled (10 °C/min) o oom empe a u e.
Q280 Solu ion ea ed o 24 h a 280 °C, hen wa e quenched o oom empe a u e.
Q310 Solu ion ea ed o 24 h a 310 °C
,
hen wa e quenched o oom empe a u e.
Q360 Solu ion ea ed o 24 h a 325 °C, hen hea ed and kep a 360 °C o 24 h and wa e
quenched.
Q380 Solu ion ea ed o 24 h a 325 °C, hen hea ed and kep a 380 °C o 24 h and wa e
quenched.
Figu e 1.
DSC cu es o he as-cas sample. Peak empe a u es du ing hea ing we e conside ed o
he he mal ea men selec ion o he samples.
We decided o subjec he samples o se en di e en he mal condi ions o y o
sepa a e and simpli y he iden i ica ion o he di e en phases appea ing and disappea ing
du ing he hea ing p ocess (Table 2and Figu e 2).
Ma e ials 2022, 15, 5056 4 o 15
(a) (b)
Figu e 2. Hea ing and cooling sequences o he samples, in addi ion o he as-cas sample. (a)
Slowly cooled (10 °C/min) samples (Eq280 and Eq360). (b) Quenched samples (Q280, Q310, Q360,
and Q380).
2.3. The modynamic Simula ions
Equilib ium and Scheil non-equilib ium solidi ica ion simula ions we e ca ied ou
wi h he CALPHAD me hod o he cas alloy composi ion wi h Fac Sage 7.3 so wa e,
along wi h he FTli e (2021) da abase. Only he ou main elemen s in he alloy we e
conside ed.
2.4. Mic os uc u al Obse a ions
As-cas and Q380 samples we e obse ed wi h scanning elec on mic oscopy (SEM
o Sho ky ield emission, JEOL JSM-7000F) and ene gy dispe si e X- ay spec oscopy
(INCA EDX de ec o X-sigh Se ie Si (Li) pen aFET Ox o d) a an elec on beam ol age
o 5.0 kV a oom empe a u e. Specimens had been p e iously cleaned, g ound, and
polished o ob ain a p ope su ace inish o he analysis.
2.5. X- ay The mo-Di ac ion Tes s
The equipmen used o he X- ay he mo-di ac ion es s was a B uke D8 Ad ance
di ac ome e ha ope a ed a 30 kV and 20 mA o e lec ion measu emen s. I was
equipped wi h a coppe anode (λ = 1.5418 Å), a Van ec-1 PSD de ec o , and an An on Pa
HTK2000 high empe a u e u nace. The sample holde used, on which he es
empe a u e was con olled, was made o pla inum.
The se en specimens, which we e 10 × 10 mm2 wi h a hickness be ween 1 and 2
mm, we e subjec ed o a hea ing cycle om 30 o 360 °C and cooling again o 30 °C in he
di ac ome e . Di ac ion es s we e pe o med a oom empe a u e (30 °C), a h ee
empe a u es du ing hea ing (260, 320, 360 °C), and a h ee empe a u es du ing cooling
(260, 180, 30 °C), based on he empe a u es o in e es ound in he DSC cu es (Figu e
3). The measu emen s we e eco ded in he ange 10° ≤ 2θ ≤ 100° a inc emen s o 0.033°,
wi h each s age las ing 0.8 s.
240
260
280
300
320
340
360
380
400
Tempe a u e (°C)
Time
Eq280
Eq360
240
260
280
300
320
340
360
380
400
Tempe a u e (°C)
Time
Q310
≈≈
≈
≈
≈
Q280
Q360 Q380
Figu e 2.
Hea ing and cooling sequences o he samples, in addi ion o he as-cas sample. (
a
) Slowly
cooled (10
◦
C/min) samples (Eq280 and Eq360). (
b
) Quenched samples (Q280, Q310, Q360, and Q380).
Ma e ials 2022,15, 5056 4 o 14
Table 2.
Hea ea men s o each sample condi ion. The wo-s ep solu ion ea men in Q360
and Q380 was applied o p e en any pa ial mel ing du ing one-s ep solu ion ea men a he
solu ion empe a u e.
Sample Condi ion Hea T ea men
as-cas None.
Eq280 Hea ed o 280 ◦C and immedia ely slowly cooled (10 ◦C/min) o oom empe a u e.
Eq360 Hea ed o 360 ◦C and immedia ely slowly cooled (10 ◦C/min) o oom empe a u e.
Q280 Solu ion ea ed o 24 h a 280 ◦C, hen wa e quenched o oom empe a u e.
Q310 Solu ion ea ed o 24 h a 310 ◦C, hen wa e quenched o oom empe a u e.
Q360 Solu ion ea ed o 24 h a 325 ◦C, hen hea ed and kep a 360 ◦C o 24 h and wa e quenched.
Q380 Solu ion ea ed o 24 h a 325 ◦C, hen hea ed and kep a 380 ◦C o 24 h and wa e quenched.
2.3. The modynamic Simula ions
Equilib ium and Scheil non-equilib ium solidi ica ion simula ions we e ca ied ou
wi h he CALPHAD me hod o he cas alloy composi ion wi h Fac Sage 7.3 so wa e, along
wi h he FTli e (2021) da abase. Only he ou main elemen s in he alloy
we e conside ed.
2.4. Mic os uc u al Obse a ions
As-cas and Q380 samples we e obse ed wi h scanning elec on mic oscopy (SEM o
Sho ky ield emission, JEOL JSM-7000F) and ene gy dispe si e X- ay spec oscopy (INCA
EDX de ec o X-sigh Se ie Si (Li) pen aFET Ox o d) a an elec on beam ol age o 5.0 kV
a oom empe a u e. Specimens had been p e iously cleaned, g ound, and polished o
ob ain a p ope su ace inish o he analysis.
2.5. X- ay The mo-Di ac ion Tes s
The equipmen used o he X- ay he mo-di ac ion es s was a B uke D8 Ad ance
di ac ome e ha ope a ed a 30 kV and 20 mA o e lec ion measu emen s. I was
equipped wi h a coppe anode (
λ
= 1.5418 Å), a Van ec-1 PSD de ec o , and an An on Pa
HTK2000 high empe a u e u nace. The sample holde used, on which he es empe a u e
was con olled, was made o pla inum.
The se en specimens, which we e 10
×
10 mm
2
wi h a hickness be ween 1 and 2 mm,
we e subjec ed o a hea ing cycle om 30 o 360
◦
C and cooling again o 30
◦
C in he
di ac ome e . Di ac ion es s we e pe o med a oom empe a u e (30
◦
C), a h ee
empe a u es du ing hea ing (260, 320, 360
◦
C), and a h ee empe a u es du ing cooling
(260, 180, 30
◦
C), based on he empe a u es o in e es ound in he DSC cu es (Figu e 3).
The measu emen s we e eco ded in he ange 10
◦≤
2
θ≤
100
◦
a inc emen s o 0.033
◦
,
wi h each s age las ing 0.8 s.
The mo-di ac ion es s we e pe o med h ee mon hs a e he samples we e p e-
pa ed. Twel e mon hs a e he p epa a ion; ha is, nine mon hs a e being subjec ed o he
he mal cycle in he he mo-di ac ome e , samples we e e es ed in he same condi ions as
be o e bu only a 30
◦
C, in o de o obse e whe he na u al p ecipi a ion had aken place.
The X- ay di ac ion pa e ns we e indexed wi h he PDF-4+ 2021 da abase om he
In e na ional Cen e o Di ac ion Da a (ICDD). Fo he sea ch o non-indexed phases,
leas squa es-based Rie eld e inemen was ca ied ou in selec ed pa e ns wi h he
FullP o so wa e (FullP o .2k Ve sion 7.40, Janua y 2021, J. Rod iguez-Ca ajal, ILL, G eno-
ble, F ance). The shape o he B agg peaks was ep esen ed by a Pseudo-Voig unc ion.
Con en ional R- alues, co ec ed o backg ound, a e gi en in he igu es as ag eemen
o he i ing o he obse ed alues [
34
,
35
]. The e m “in ensi y” is used o e e o he
“in eg a ed in ensi y”.
Ma e ials 2022,15, 5056 5 o 14
Ma e ials 2022, 15, 5056 5 o 15
Figu e 3. The mal cycle o he samples in he he mo-di ac ome e . Measu emen s we e
pe o med a he empe a u es indica ed in each s ep.
The mo-di ac ion es s we e pe o med h ee mon hs a e he samples we e
p epa ed. Twel e mon hs a e he p epa a ion; ha is, nine mon hs a e being subjec ed
o he he mal cycle in he he mo-di ac ome e , samples we e e es ed in he same
condi ions as be o e bu only a 30 °C, in o de o obse e whe he na u al p ecipi a ion
had aken place.
The X- ay di ac ion pa e ns we e indexed wi h he PDF-4+ 2021 da abase om he
In e na ional Cen e o Di ac ion Da a (ICDD). Fo he sea ch o non-indexed phases,
leas squa es-based Rie eld e inemen was ca ied ou in selec ed pa e ns wi h he
FullP o so wa e (FullP o .2k Ve sion 7.40, Janua y 2021, J. Rod iguez-Ca ajal, ILL,
G enoble, F ance). The shape o he B agg peaks was ep esen ed by a Pseudo-Voig
unc ion. Con en ional R- alues, co ec ed o backg ound, a e gi en in he igu es as
ag eemen o he i ing o he obse ed alues [34,35]. The e m “in ensi y” is used o
e e o he “in eg a ed in ensi y”.
3. Resul s
3.1. The modynamic Simula ion Resul s
The modynamic simula ions pe o med wi h Fac Sage o equilib ium cooling
condi ions (Figu e 4a) p edic ed a high p opo ion o he FCC aluminum solid solu ion a
empe a u es be ween 360 and 380 °C, wi h he Si and Mg2Si phases being p ecipi a ed a
hese empe a u es. As cooling wen on, he solid solu ion decomposed and a ound 350
°C a second aluminum phase (Al#2) was gene a ed bu disappea ed soon a e . This
phase would co espond o he zinc- ich α’ aluminum phase o he miscibili y gap in he
Al–Zn sys em [36,37]. A abou 340 °C, he in e me allic phase Mg2Zn11 was o med, and
MgZn2 p ecipi a ed om Mg2Zn11 a a ound 140 °C. The simula ion unde
non-equilib ium condi ions (Scheil app oxima ion) p edic ed he p ecipi a ion o
Mg2Zn11 and MgZn2 a abou 370 °C and ha o hexagonal zinc a 350 °C (Figu e 4b).
30
260
320
360
260
180
30
0
50
100
150
200
250
300
350
400
0 50 100 150 200 250 300 350
Tempe a u e (°C)
Time
10 °C/min
Figu e 3.
The mal cycle o he samples in he he mo-di ac ome e . Measu emen s we e pe o med
a he empe a u es indica ed in each s ep.
3. Resul s
3.1. The modynamic Simula ion Resul s
The modynamic simula ions pe o med wi h Fac Sage o equilib ium cooling con-
di ions (Figu e 4a) p edic ed a high p opo ion o he FCC aluminum solid solu ion a
empe a u es be ween 360 and 380
◦
C, wi h he Si and Mg
2
Si phases being p ecipi a ed a
hese empe a u es. As cooling wen on, he solid solu ion decomposed and a ound 350
◦
C
a second aluminum phase (Al#2) was gene a ed bu disappea ed soon a e . This phase
would co espond o he zinc- ich
α
’ aluminum phase o he miscibili y gap in he Al–Zn
sys em [
36
,
37
]. A abou 340
◦
C, he in e me allic phase Mg
2
Zn
11
was o med, and MgZn
2
p ecipi a ed om Mg
2
Zn
11
a a ound 140
◦
C. The simula ion unde non-equilib ium condi-
ions (Scheil app oxima ion) p edic ed he p ecipi a ion o Mg
2
Zn
11
and MgZn
2
a abou
370 ◦C and ha o hexagonal zinc a 350 ◦C (Figu e 4b).
Ma e ials 2022, 15, 5056 6 o 15
(a) (b)
Figu e 4. The modynamic simula ions wi h Fac Sage o he s udied alloy conside ing (a)
equilib ium solidi ica ion condi ions and (b) non-equilib ium solidi ica ion (Scheil model).
3.2. Mic os uc u e o he Samples Depending on he Ini ial The mal Condi ion
The mic os uc u e esul ing om he as-cas s a e was he e ogeneous, wi h
di e en phases dis ibu ed h oughou he in e dend i ic egion depending on he
solidi ica ion a e (Figu e 5a). In he Q380 condi ion (Figu e 5b), he globuliza ion and
educ ion in he size o he phases a e he solu ion ea men we e ema kable. The Si,
Mg–Si, and Mg–Zn phases we e ound by EDX measu emen s. The Si phase solidi ied in
ce ain a eas as eu ec ic and in o he a eas as p ima y silicon. In addi ion, isola ed Al–Fe–
Mg–Si phases we e de ec ed.
(a) (b)
Figu e 4.
The modynamic simula ions wi h Fac Sage o he s udied alloy conside ing (
a
) equilib ium
solidi ica ion condi ions and (b) non-equilib ium solidi ica ion (Scheil model).
Ma e ials 2022,15, 5056 6 o 14
3.2. Mic os uc u e o he Samples Depending on he Ini ial The mal Condi ion
The mic os uc u e esul ing om he as-cas s a e was he e ogeneous, wi h di e en
phases dis ibu ed h oughou he in e dend i ic egion depending on he solidi ica ion a e
(Figu e 5a). In he Q380 condi ion (Figu e 5b), he globuliza ion and educ ion in he size o
he phases a e he solu ion ea men we e ema kable. The Si, Mg–Si, and Mg–Zn phases
we e ound by EDX measu emen s. The Si phase solidi ied in ce ain a eas as eu ec ic and
in o he a eas as p ima y silicon. In addi ion, isola ed Al–Fe–Mg–Si phases we e de ec ed.
Ma e ials 2022, 15, 5056 6 o 15
(a) (b)
Figu e 4. The modynamic simula ions wi h Fac Sage o he s udied alloy conside ing (a)
equilib ium solidi ica ion condi ions and (b) non-equilib ium solidi ica ion (Scheil model).
3.2. Mic os uc u e o he Samples Depending on he Ini ial The mal Condi ion
The mic os uc u e esul ing om he as-cas s a e was he e ogeneous, wi h
di e en phases dis ibu ed h oughou he in e dend i ic egion depending on he
solidi ica ion a e (Figu e 5a). In he Q380 condi ion (Figu e 5b), he globuliza ion and
educ ion in he size o he phases a e he solu ion ea men we e ema kable. The Si,
Mg–Si, and Mg–Zn phases we e ound by EDX measu emen s. The Si phase solidi ied in
ce ain a eas as eu ec ic and in o he a eas as p ima y silicon. In addi ion, isola ed Al–Fe–
Mg–Si phases we e de ec ed.
(a) (b)
Ma e ials 2022, 15, 5056 7 o 15
Figu e 5. SEM mic og aphs o he ma e ial wi h x1000 magni ica ion (a) As-cas . (b) Q380.
Numbe s 1 o 4 e e o he EDX esul s p o ided below. 1: Al-Zn ma ix, 2: Mg-Zn phases, 3: Si
phases and 4: Mg-Si phases.
As o he ma ix, i showed a wo-phase mic os uc u e o aluminum and zinc.
P ecipi a ion o he Zn phase was obse ed in he as-cas ma e ial, unlike in sample Q380,
whe e he Zn phase was no de ec ed, indica ing ha i was dissol ed wi hin he ma ix
(Figu e 6).
(a) (b)
Figu e 6. SEM mic og aphs o he Al–Zn ma ix. (a) As-cas . (b) Q380.
The iden i ica ion o he phases p esen in each ini ial he mal condi ion was
pe o med by oom empe a u e X- ay di ac ion (be o e he hea ing cycle). As is shown
in Figu e 7, in addi ion o he Al phase (PDF: 00-004-0787) and he P phase om he
sample holde (PDF: 04-013-4766), which a e no indica ed o cla i y, he phases de ec ed
we e Zn (PDF: 01-078-9363), Si (PDF: 00-027-1402), MgZn
2
(PDF: 04-003-2083), Mg
2
Zn
11
(PDF: 04-007-1412), and Mg
2
Si (PDF: 01-083-5235).
Figu e 5.
SEM mic og aphs o he ma e ial wi h
×
1000 magni ica ion (
a
) As-cas . (
b
) Q380. Numbe s
1 o 4 e e o he EDX esul s p o ided below. 1: Al-Zn ma ix, 2: Mg-Zn phases, 3: Si phases and
4: Mg-Si phases.
As o he ma ix, i showed a wo-phase mic os uc u e o aluminum and zinc.
P ecipi a ion o he Zn phase was obse ed in he as-cas ma e ial, unlike in sample Q380,
Ma e ials 2022,15, 5056 7 o 14
whe e he Zn phase was no de ec ed, indica ing ha i was dissol ed wi hin he ma ix
(Figu e 6).
Ma e ials 2022, 15, 5056 7 o 15
Figu e 5. SEM mic og aphs o he ma e ial wi h x1000 magni ica ion (a) As-cas . (b) Q380.
Numbe s 1 o 4 e e o he EDX esul s p o ided below. 1: Al-Zn ma ix, 2: Mg-Zn phases, 3: Si
phases and 4: Mg-Si phases.
As o he ma ix, i showed a wo-phase mic os uc u e o aluminum and zinc.
P ecipi a ion o he Zn phase was obse ed in he as-cas ma e ial, unlike in sample Q380,
whe e he Zn phase was no de ec ed, indica ing ha i was dissol ed wi hin he ma ix
(Figu e 6).
(a) (b)
Figu e 6. SEM mic og aphs o he Al–Zn ma ix. (a) As-cas . (b) Q380.
The iden i ica ion o he phases p esen in each ini ial he mal condi ion was
pe o med by oom empe a u e X- ay di ac ion (be o e he hea ing cycle). As is shown
in Figu e 7, in addi ion o he Al phase (PDF: 00-004-0787) and he P phase om he
sample holde (PDF: 04-013-4766), which a e no indica ed o cla i y, he phases de ec ed
we e Zn (PDF: 01-078-9363), Si (PDF: 00-027-1402), MgZn
2
(PDF: 04-003-2083), Mg
2
Zn
11
(PDF: 04-007-1412), and Mg
2
Si (PDF: 01-083-5235).
Figu e 6. SEM mic og aphs o he Al–Zn ma ix. (a) As-cas . (b) Q380.
The iden i ica ion o he phases p esen in each ini ial he mal condi ion was pe o med
by oom empe a u e X- ay di ac ion (be o e he hea ing cycle). As is shown in Figu e 7,
in addi ion o he Al phase (PDF: 00-004-0787) and he P phase om he sample holde
(PDF: 04-013-4766), which a e no indica ed o cla i y, he phases de ec ed we e Zn (PDF: 01-
078-9363), Si (PDF: 00-027-1402), MgZn
2
(PDF: 04-003-2083), Mg
2
Zn
11
(PDF: 04-007-1412),
and Mg2Si (PDF: 01-083-5235).
Ma e ials 2022, 15, 5056 8 o 15
(a) (b)
Figu e 7. Di ac ion pa e ns o he samples in each he mal condi ion a 30 °C p io o he hea ing
cycle in he he mo-di ac ome e . Indexa ion is shown abo e he pa e ns o samples Eq280
(Mg
2
Zn
11
and Mg
2
Si phases) and Eq360 (Si, Zn and MgZn
2
phases). Peaks co esponding o Al and
P phases ( he la e om he sample holde ) a e omi ed o cla i y. (a) As-cas samples and hose
cooled slowly. (b) Quenched samples.
Howe e , he mic os uc u e ob ained depended on he applied ea men ; ha is,
he empe a u e a which cooling had s a ed and he cooling a e. In as-cas condi ions
Zn p ecipi a ed, as did bo h MgZn
2
and Mg
2
Zn
11
o a lesse ex en . When slowly cooling
om 280 °C (Eq280 sample), MgZn
2
was ob ained again, as in he p e ious case, bu now
Mg
2
Zn
11
p ecipi a ed p e e en ially, while HCP Zn was ha dly de ec ed. When he
cooling began a 360 °C (Eq360 sample), on he o he hand, no p ecipi a ion o Mg
2
Zn
11
was obse ed and zinc was p esen in he HCP Zn and MgZn
2
phases. MgZn
2
phases
we e ound in g ea e quan i ies han in he as-cas o Eq280 condi ions. As o he
quenched samples, he Mg
2
Zn
11
phase was dissol ed when eaching 360 °C.
Rega ding he Fe-bea ing qua e na y phases obse ed by SEM, i was no possible o
con i m hem by X- ay di ac ion. The mos in ense B agg peak o Al
8
FeMg
3
Si
6
(PDF:
03-065-5936) would o e lap wi h he Al (111) e lec ion. Gi en i s condi ion as a mino
phase, u he peaks could no be de ec ed. The e o e, i o he Cu- and Fe-bea ing phases
ound in aluminum alloys con aining Zn, Mg, Si, and/o Cu [38,39] we e p esen in e y
small amoun s in his alloy, speci ic X- ay di ac ion condi ions and equipmen would
be equi ed o iden i y hem.
The appea ance o he Mg
2
Si phase and he dissolu ion and p ecipi a ion o he Zn
phase a e discussed in he ollowing sec ion.
3.3. E olu ion o he HCP Zn and In e me allic Phases wi h Tempe a u e
The p o iles ob ained o he as-cas sample a e ep esen a i e o he e olu ion o he
zinc-con aining phases wi h empe a u e (Figu e 8). The desc ip ion is hus alid o he
es o he samples, while he ma ix will be deal wi h in he nex sec ion. This e olu ion
is summa ized below.
Figu e 7.
Di ac ion pa e ns o he samples in each he mal condi ion a 30
◦
C p io o he hea -
ing cycle in he he mo-di ac ome e . Indexa ion is shown abo e he pa e ns o samples Eq280
(Mg
2
Zn
11
and Mg
2
Si phases) and Eq360 (Si, Zn and MgZn
2
phases). Peaks co esponding o Al and
P phases ( he la e om he sample holde ) a e omi ed o cla i y. (
a
) As-cas samples and hose
cooled slowly. (b) Quenched samples.
Howe e , he mic os uc u e ob ained depended on he applied ea men ; ha is,
he empe a u e a which cooling had s a ed and he cooling a e. In as-cas condi ions
Zn p ecipi a ed, as did bo h MgZn
2
and Mg
2
Zn
11
o a lesse ex en . When slowly cooling
om 280
◦
C (Eq280 sample), MgZn
2
was ob ained again, as in he p e ious case, bu now
Ma e ials 2022,15, 5056 8 o 14
Mg
2
Zn
11
p ecipi a ed p e e en ially, while HCP Zn was ha dly de ec ed. When he cooling
began a 360
◦
C (Eq360 sample), on he o he hand, no p ecipi a ion o Mg
2
Zn
11
was
obse ed and zinc was p esen in he HCP Zn and MgZn
2
phases. MgZn
2
phases we e
ound in g ea e quan i ies han in he as-cas o Eq280 condi ions. As o he quenched
samples, he Mg2Zn11 phase was dissol ed when eaching 360 ◦C.
Rega ding he Fe-bea ing qua e na y phases obse ed by SEM, i was no possible o
con i m hem by X- ay di ac ion. The mos in ense B agg peak o Al
8
FeMg
3
Si
6
(PDF:
03-065-5936) would o e lap wi h he Al (111) e lec ion. Gi en i s condi ion as a mino
phase, u he peaks could no be de ec ed. The e o e, i o he Cu- and Fe-bea ing phases
ound in aluminum alloys con aining Zn, Mg, Si, and/o Cu [
38
,
39
] we e p esen in e y
small amoun s in his alloy, speci ic X- ay di ac ion condi ions and equipmen would be
equi ed o iden i y hem.
The appea ance o he Mg
2
Si phase and he dissolu ion and p ecipi a ion o he Zn
phase a e discussed in he ollowing sec ion.
3.3. E olu ion o he HCP Zn and In e me allic Phases wi h Tempe a u e
The p o iles ob ained o he as-cas sample a e ep esen a i e o he e olu ion o he
zinc-con aining phases wi h empe a u e (Figu e 8). The desc ip ion is hus alid o he
es o he samples, while he ma ix will be deal wi h in he nex sec ion. This e olu ion is
summa ized below.
Ma e ials 2022, 15, 5056 9 o 15
(a) (b)
Figu e 8. Di ac ion pa e ns o he as-cas sample showing he e olu ion o he in e me allic
phases, Zn, and Si wi h empe a u e (a) du ing he hea ing cycle ( om 30 o 360 °C) (b) and cooling
cycle ( om 360 o 30 °C) in he he mo-di ac ome e . The main B agg peaks o he S Zn
13
phase
a e iden i ied.
A 30 °C, Zn, MgZn
2
, and Mg
2
Zn
11
phases we e ound. A 260 °C, he in ensi y o Zn
peaks dec eased while wo addi ional B agg peaks we e de ec ed a ound 2θ = 35.9° and
2θ = 54.0°. These peaks did no belong o any o he phases al eady indexed. Assuming
hey belonged o a new phase, i was clea ha i a ose a a empe a u e be ween 30 and
260 °C and likely dissol ed be ween 260 and 280 °C, since i was absen in he Q280
sample a oom empe a u e and in all he samples a any o he empe a u e du ing he
hea ing cycle. Indexing was pe o med conside ing mino elemen s p esen in he alloy,
such as Cu, Fe, and S , and inally he S Zn
13
phase was iden i ied (PDF: 04-013-4885).
A 320 °C, bo h Zn and S Zn
13
we e dissol ed. In addi ion, be ween 30 and 320 °C
he in ensi y o Mg
2
Zn
11
inc eased and hen became negligible a 360 °C. F om he
inc ease in he in ensi y o he MgZn
2
peaks a his empe a u e, i ollowed ha Mg
2
Zn
11
had no comple ely dissol ed in he ma ix and may ha e become he MgZn
2
phase.
Rega ding he cooling cycle, he onse o he p ecipi a ion o he Mg
2
Zn
11
phase was
obse ed a 260 °C, while ha o he Zn phase was no de ec ed un il 180 °C. A his
empe a u e, he peaks belonging o S Zn
13
showed sligh ly and disappea ed again wi h
u he cooling. I should be no ed ha in he inal measu emen a 30 °C, he dis ibu ion
o p ecipi a ed phases was di e en om wha i had been a he beginning. The
p opo ion o MgZn
2
ob ained a 360 °C emained s able du ing cooling and was highe
han ha ound du ing he ini ial measu emen .
No e olu ion wi h empe a u e was obse ed o he Mg
2
Si phase. The e we e
di icul ies wi h de ec ing i in some o he measu emen s (see di e ences in Figu e 7),
bu his was ela ed o he speci ic sample (local seg ega ions o inhomogenei ies) and
no o ans o ma ions aking place wi h empe a u e.
3.4. E olu ion o Aluminum Phases
As was p e iously men ioned, a wo-phase Al–Zn ma ix was ound. Howe e , a
de ailed obse a ion o he indexed p o iles led o he de ec ion o some peaks whose
in ensi y was highe han expec ed. These obse a ions we e con i med when
Figu e 8.
Di ac ion pa e ns o he as-cas sample showing he e olu ion o he in e me allic
phases, Zn, and Si wi h empe a u e (
a
) du ing he hea ing cycle ( om 30 o 360
◦
C) (
b
) and cooling
cycle ( om 360 o 30
◦
C) in he he mo-di ac ome e . The main B agg peaks o he S Zn
13
phase
a e iden i ied.
A 30
◦
C, Zn, MgZn
2
, and Mg
2
Zn
11
phases we e ound. A 260
◦
C, he in ensi y o Zn
peaks dec eased while wo addi ional B agg peaks we e de ec ed a ound 2
θ
= 35.9
◦
and
2θ= 54.0◦.
These peaks did no belong o any o he phases al eady indexed. Assuming
hey belonged o a new phase, i was clea ha i a ose a a empe a u e be ween 30 and
260
◦
C and likely dissol ed be ween 260 and 280
◦
C, since i was absen in he Q280 sample
a oom empe a u e and in all he samples a any o he empe a u e du ing he hea ing
cycle. Indexing was pe o med conside ing mino elemen s p esen in he alloy, such as
Cu, Fe, and S , and inally he S Zn13 phase was iden i ied (PDF: 04-013-4885).
Ma e ials 2022,15, 5056 9 o 14
A 320
◦
C, bo h Zn and S Zn
13
we e dissol ed. In addi ion, be ween 30 and 320
◦
C he
in ensi y o Mg
2
Zn
11
inc eased and hen became negligible a 360
◦
C. F om he inc ease
in he in ensi y o he MgZn2peaks a his empe a u e, i ollowed ha Mg2Zn11 had no
comple ely dissol ed in he ma ix and may ha e become he MgZn2phase.
Rega ding he cooling cycle, he onse o he p ecipi a ion o he Mg
2
Zn
11
phase was
obse ed a 260
◦
C, while ha o he Zn phase was no de ec ed un il 180
◦
C. A his
empe a u e, he peaks belonging o S Zn
13
showed sligh ly and disappea ed again wi h
u he cooling. I should be no ed ha in he inal measu emen a 30
◦
C, he dis ibu ion
o p ecipi a ed phases was di e en om wha i had been a he beginning. The p opo ion
o MgZn
2
ob ained a 360
◦
C emained s able du ing cooling and was highe han ha
ound du ing he ini ial measu emen .
No e olu ion wi h empe a u e was obse ed o he Mg
2
Si phase. The e we e di i-
cul ies wi h de ec ing i in some o he measu emen s (see di e ences in Figu e 7), bu his
was ela ed o he speci ic sample (local seg ega ions o inhomogenei ies) and no o ans-
o ma ions aking place wi h empe a u e.
3.4. E olu ion o Aluminum Phases
As was p e iously men ioned, a wo-phase Al–Zn ma ix was ound. Howe e ,
a de ailed obse a ion o he indexed p o iles led o he de ec ion o some peaks whose
in ensi y was highe han expec ed. These obse a ions we e con i med when pe o ming
a Rie eld i ing on one o he p o iles (Eq280 sample a 30
◦
C, be o e hea ing). I was
e i ied ha some o he peaks could no be i ed wi h he o iginal model and he e was
a phase missing (Figu e 9a). The addi ion o a phase wi h he same spa ial g oup as
aluminum (
Fm3m
) bu a smalle la ice pa ame e managed o sol e he s uc u al model
wi h sa is ac o y p ecision (Figu e 9b). Due o he smalle a omic size o zinc compa ed
o aluminum, a zinc- ich aluminum phase would show a smalle la ice pa ame e han
α
-Al and hus i s B agg peaks would shi o g ea e angles [
32
]. The e o e, he new phase
obse ed could be he zinc- ich
α
’ aluminum me as able phase o he miscibili y gap in
he Al–Zn sys em. The samples we e e es ed wi h oom empe a u e X- ay di ac ome y
nine mon hs la e wi h he aim o de e mining whe he his was he case, and i was ound
ha p ecipi a ion o he Zn phase om he α’ me as able phase had aken place.
Ma e ials 2022, 15, 5056 10 o 15
pe o ming a Rie eld i ing on one o he p o iles (Eq280 sample a 30 °C, be o e
hea ing). I was e i ied ha some o he peaks could no be i ed wi h he o iginal model
and he e was a phase missing (Figu e 9a). The addi ion o a phase wi h he same spa ial
g oup as aluminum (𝐹𝑚3
𝑚) bu a smalle la ice pa ame e managed o sol e he
s uc u al model wi h sa is ac o y p ecision (Figu e 9b). Due o he smalle a omic size o
zinc compa ed o aluminum, a zinc- ich aluminum phase would show a smalle la ice
pa ame e han α-Al and hus i s B agg peaks would shi o g ea e angles [32].
The e o e, he new phase obse ed could be he zinc- ich α’ aluminum me as able phase
o he miscibili y gap in he Al–Zn sys em. The samples we e e es ed wi h oom
empe a u e X- ay di ac ome y nine mon hs la e wi h he aim o de e mining whe he
his was he case, and i was ound ha p ecipi a ion o he Zn phase om he α’
me as able phase had aken place.
(a) (b)
Figu e 9. Rie eld i ing o he Eq280 sample a 30 °C (be o e hea ing) wi h FullP o so wa e. Red
do s: expe imen al da a. Black line: Fi ing da a. (a) The ollowing six phases a e conside ed Al (a =
4.0428 Å), Zn, Si, MgZn
2
, Mg
2
Zn
11
, and Mg
2
Si. The P phase comes om he sample holde . R- alues
wi h backg ound co ec ion: R
p
= 36.6 %, R
wp
= 38.6 %, R
exp
= 10.72 %, χ
2
= 12.91. (b) An α’ phase
wi h a la ice pa ame e a = 4.0089 Å is added o he p e ious case. Al phase in (a) is now labeled as
α-Al. R- alues wi h backg ound co ec ion: R
p
= 20.5 %, R
wp
= 18.7 %, R
exp
= 10.54 %, χ
2
= 3.15.
The e olu ion o he in ensi y o he B agg peak co esponding o he (101) plane o
he Zn phase was obse ed (Figu e 10). The eason o choosing his peak is simple: i is
he one wi h he maximum in ensi y o he Zn phase and i does no o e lap wi h signals
belonging o any o he phase. Fo hese easons, his e lec ion is one o hose aken as a
e e ence in p ecipi a ion s udies o Al–Zn alloys [31]. In ensi y inc eased in all cases,
al hough only ou o hem a e shown in he igu e.
Figu e 9.
Rie eld i ing o he Eq280 sample a 30
◦
C (be o e hea ing) wi h FullP o so wa e. Red
do s: expe imen al da a. Black line: Fi ing da a. (
a
) The ollowing six phases a e conside ed Al
(a = 4.0428 ˚
A),
Zn, Si, MgZn
2
, Mg
2
Zn
11
, and Mg
2
Si. The P phase comes om he sample holde .
R- alues wi h backg ound co ec ion: R
p
= 36.6 %, R
wp
= 38.6 %, R
exp
= 10.72 %,
χ2
= 12.91. (
b
) An
α
’ phase wi h a la ice pa ame e a = 4.0089
˚
A
is added o he p e ious case. Al phase in (a) is now
labeled as
α
-Al. R- alues wi h backg ound co ec ion: R
p
= 20.5 %, R
wp
= 18.7 %, R
exp
= 10.54 %,
χ2= 3.15.
