2024--T3和2524--T34铝合金疲劳裂纹的萌生机制

1

Vol.25No.1February2011

2011

2

CHINESEJOURNALOFMATERIALSRESEARCH

2024–T32524–T34

∗

1

1

2

1.2.

621000

610065

2024–T3

2524–T34,

,

0.1

15Hz

:,

,

,

2024

,

2524

2524

Fe

β

,

;

2024

2524

,

,

,

,

TG111

1005-3093(2011)01-0067-06

TheMechanismofFatigueCrackInitiationof2024–T3and

2524–T34AluminumAlloys

LITang1

TAOJunlin1

WANGQingyuan2∗∗

1.CollegeofCivilEngineeringandArchitecture,SouthwestUniversityofScienceandTechnology,Mianyang621000

2.DepartmentofEngineeringMechanics,SichuanUniversity,Chengdu610065

*SupportedbyNationalFundsforDistinguishedYoungScientistsofChinaNo.10925211andSouthwestUniversityofScienceandTechnologyFundsforDoctorsNo.08ZX0108.ManuscriptreceivedJune11,2010;inrevisedformNovember15,2010.

**Towhomcorrespondenceshouldbeaddressed,Tel:(028)806919,E–mail:wangqy@scu.edu.cn

ABSTRACTThemicrostructureandmechanismoffatiguecrackinitiationof2024–T3and2524–T34Alalloyswereinvestigated.Four–pointbendingandtension–tensionfatiguetestsonthetestedalloyswithafrequencyof15Hz,R=0.1alongtherollingdirectionwereconductedatroomtemperature.Itwasfoundthattheflatgrainwaselongatedalongtherollingdirection,showingthelaminargrainstructure.Theamountofcoarseandirregularparticlesandthedensityofsecondaryparticlesdistributedin2024weremuchhigherthanthatin2524.Particlesin2524distributedstrippedalongtherollingdirection.Themajorityoffatiguecracksof2524wereinitiatedonthecoarseβphasesecondparticle,containingFe,afewofthemformedonsitesofmaterialdefectsorslipbands.TheintrusionandextrusioninducedbyslipbandintheAlcladdinglayerprovidedprincipalfatiguecrackinitiationsitesfor2024and2524Al–claddingaluminumalloys.

KEYWORDSfoundationaldisciplineinmaterialsscience,aluminumalloy,thesecond–phaseparticle,fatiguecrack,fatiguecrackinitiation1931

,2024

2524

,

2024–T3

20

90

,

,

(AluminumCompanyofAmerica)

10925211

,

(constituentparticles)

*

,

08ZX0108

2024

11

,,

2010

6

2010

11

15

[1−8]

:

,

2524

[9−13]

68

25

2000

θ󰀂(Al2Cu)

5.08mm;

T34;

2024–O

S󰀂(Al2CuMg)

,

2.mm,

,

Al–Cu

,

T3

,

2024–O

:495

,

,,

(

427

)

5.3

/min,

,,

0.9

/min,

40min;

,

3%

,

12524

,

374MPa,

484MPa,

18.2%;2024

303MPa,

386MPa,

[1−6]

,

14%

,

[14]

,

,

2524

[14]

,2024

[1]

MTS810

INSTRON8800R=0.1,

,,

,

15Hz,

[1−6]

Zabett

Plumtree[1]Bowels[2]

,

500

,

:2024

–

;2524

,

;2524

Grosskreutz

Shaw[3]

,

,

(

FeSi

(inclusion

)

clusters)

Kung

Fine[4]

,

[15]

,

HitachiS–4300

(SEM)

β

(Al7Cu2Fe)

,

S

Olympus

(Al2CuMg)

,

[5,6]

Newman

2

2.1

Edwards[7]

,

2024–T3

(inclusionclusters)

,

1

2024

2524LS

,

,

LTST

2024

,

:L

,S

,

,T

;LT

[8]

,ST

,LS

1

,

,

2024,

2524

,

,,

,

,

2524

1

,

,

(

):

(Al,

2024

,

cladding)

2524

–T34

12524

2024

Table1ChemicalcompositionofAlalloys2524and2024(massfraction,%)

Element25242024

Si0.060.50

Fe0.120.50

Cu4.0–4.53.8–4.9

Mn0.45–0.70.3–0.9

Mg1.2–1.61.2–1.8

Cr0.050.10

Zn0.150.25

Ti0.100.15

AlRes.Res.

1

:2024–T3

2524–T34

69

1

2024–T3

2524–T34

Fig.1Triplanaropticalmicrographillustratingthegrainstructureandmorphologyof2024–T3(a)

and2524–T34(b)Alalloy

2

2024–T3

Fig.2Opticalmicrographofsecond–particlesof2024–T3aluminumalloy

2.2

EDS

S

(Al2CuMg),

θ

(Al2Cu)

2b

,

3

2024–T3

2024

,

,

3b

3a

,

,

,

(

,

2)

,

3b

EDS

,

(

,

2a

;

2b

)

AlCuMnFe

,

Si;

Al

Cu

[1−6]

2524

,

(10–40µm)EDS

,

AlCuMnFe

SEM

EDS

Si

β

,Al7Cu2Fe,

,

2524

[16]

[17–19]

:

Al–Cu–Mg,

:

,

Ω󰀂

,Al20Cu6(Fe,

Fe

()Mn

β

(Al7Cu2Fe,

Mn)3

2024),

7XXX,

Al2Cu2(FeMn)3)Fe(

4a);

AlCu

θ

Al7Cu2(Fe,Mn)[4,20]

(

θ󰀂

(Al2Cu)

AlCuMg

S

(

4b);

2b

bc

Al20Cu2Mn3(dispersoids)(

4a)

70

25

3

2024–T3

Fig.3SEMimagesforsecond–phaseparticlesbroken(a)anditsmagnifiedimage(b)in2024–T3

4

2524–T34

Fig.4SEMmicrographsofirregularandrectangularparticles(a)andsphericalparticle(b)in2524–T3

aluminumalloy

52524

Fig.5Imagesof2524Alalloyshowingcrackinitiationsitesatstripdistributionzoneofthesecond–

phaseparticles(a),materialdefects(b),largeandirregularparticle(c)andsphericalparticle(d)

1

:2024–T3

2524–T34

71

6

2024

(σmax=0.4σy,Nf=1.48×106)(a)

,(b)

Fig.6SEMmicrographforfracturesurfaceof2024specimen(σmax=0.4σy,Nf=1.48×106),(a)fatigue

crackinitiationsites,(b)brokenparticlesinfracturezone

7

2524

Fig.7SEMmicrographforfracturesurfaceof2524specimen,(a)fatiguecrackinitiationsitesinAl

cladding(σmax=1.06σy,Nf=7.06×104),(b)fatiguecrackinitiatedatparticles(σmax=1.3σy,Nf=5.43×104)

,

4a

,

,

2.3

,

,

,

,

2524

2524

2024

,

(

5a)(

(

7a),

,

,

5c),

(

5b)

2524

,

5d

,

θ

(

7b)

,

3

1.2024

140%σy

2524

,

θ

,

β

,

,

2.

2024

,

,

θ

Fe

()Mn;

2.4

AlCu

θ

Al,Cu,Mg

S

2524

2024

,

,

Fe

()Mn

β

;

AlCu

θ

Al,Cu,Mg

S

;

(

6a)

,

Mn

Al20Cu2Mn3

,

,

3.2024

2524

,

,

6b

(

)

722524

Fe

β

,

,

,

θ

Dr.Zhai

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