·.

, ,

D

OTICELECTEDEC 28 1981September 1981

8

Report 2339

by

Dario'A. EmericSidney Levine'

K,athryn L. Washburn.,

Approved for public release; distribution unlimited.

u'.s. ARMY MOBILITY EQUIPMENT'

RESEARCH AND' DEVELOPMENT, COMMAND

FORT BELVOIR, VIRGINIA

FATIGUE STRENGTH OF ALUMINUMAL.LOYS '

THE EFFECT OFSURFACE COATINGS ON THE

•

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The citatiQn in th;sreport of trad6 names ofcommercially available. products does not constitu.teofficial endonement or approval of the use of suchprOducts.

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REPORT DOCUMENTATION PAGE READ INSTRUCTIONSBEFORE C'OMPLETINn FORM

I REPORT NUMBER \2 GOVT ACCESSION NO.3 RECIPIENf'S CATALOG NUM~Eh

,t j \ 'J ~) I j' ~ J ~" TITLE rend Subtitle)

1'IIl' "1-1'1'(1 Of- SllRl:\CI· «')AIIN<;S 0\ I HI,I' ATI< ;llj· SIR I· Nt ;'11·1 ()I,\ ( I'M INU\1 ..\ L IOYS

5 TYPE OF REPORT & PERIOD COVERED

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1hnl) ,\, f· IllCflL. Sidnl')' I.l'\ I Ill' . Kathryn L. \Va~hhl1rn

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11. CONTROLLI!'lG OFFICE NAME AND ADDRESS 12, REPORT D~,TE

t·S '-\rll.lY \1phJlity I-quiptllc-nt Rl'sl'ardl and Dl'\'I..'lopl11cnt

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AplirO\'l'd for pllhliL' rl'ka~e: di~trihution unlimited.

17. DISTRIBUTION'STATEMENT (ofth. eb.trect et.fer.d In Block 10, It different from,Rttport)

\8, SUPPLEMENTARV NOTES

19. KEY WORDS (Continue on reverae .ide /l nec•••ary ....ld IdC'rntity by block number)

AnodizingIntl..'gral Color Anodi/in~lIard ("na,tAlurninllrnShotPI..'~nin1.!

Fatigue Endurancl'Surfacc Coatin1!sBridgesV,,-'hidl'~

. An inycstigation to dl..'tl'nn\ne till' 1'lT:ct of ,;urfacc coatings on alumirium alioysand' how the coatings affect the fatig'ul' strength of alUI1,linurn in a positive or negativemanner. Kl'pnrt indudl'~ details of laboratory tc'sts corllparing different anoJiL processes

and surfa,,'e trl'atTlll'nts·( shot pel'fling).

DO FORtI'JMn 103 ED,TlON OF , NOV 65 IS :'8S9LETE

UN('LASSII"IF [)SECURHY CLAS.sIFICATlO~OF THIS PAGE ('""'" Det,. Ent.r.d)

;'r

5. Results

III I)ISCUSSI()N

22

v

iv

3

Pag(~

12

13

, iv

I LLUSTRATl()NS

Title

\11,"r·'R IC' ,( '( )NVI" RSI()N I:/\('T()RS

CON1~ENTS

TABLrs

INTR()DU( 'TJ()N

I. Statcrnent of the Prohlern"' Background

3. Approach to the Problem

4. Selection of the Best Surface Treatn1cnt and/or Coating

Section

IV C()NCLUSIC)NS

ill

BIBLIC)C;RAPIIY

h, Conclusions

Aeee9510n lor._--................ftIS, GRAlll)TIC TAB ' 0Unannounced 0J~st1tlcat1oD-----

By· --------tDistributionl.~val18bl11ty Codes

,Avail and/or

r:~ i special

_.1__.1.

Figl.re

, 3

4

5

6

8

9

Table

2

ILLUSTRATIONS

Title

t IntreatedTop Surface

Shot-Peened Top Surface

Anodized-Unsealed Top Surface

Shot-Peened and Anodized-Unsealed Top Surfa(.~

Shot-Pre-ned and Anodized-Unsealed Coating Heated to 3440 F

( 20 hours) and Exposed to Salt-Spray Test (336 Hours)

Untreated Surface-Fracture of the Fatigue (oupon (Vibrating End)

'. Shot-Peened Surface-Fracture of the Fatigue Coup0n (VibratingEnd)

Shot-Peened Surface with l1.n Un~ealed A.nc.;i~ Coating-Frac~ure

of the Coupon (yibrating End)

'unsealed Anodic Coating- Fracture of the Coupon (Vibrating End)

.TABLES

Title

Alumi,nurn Alloy. (06) -T6

Aluminunl Alloy 7075-T6

iv

Page

6

6

7

7

8

9

10

11

11

.:Page

4

5

i'vlETRlC CONVERSION' FACTORSApproximate Co.nver~lon~ to \Ietric "lea~ure~

..2.Lmbo! Whttn YIJU ~nu~ \Iuhlpj\ b" 1~() FinciLEJ~G'rH

Svmbol

l.nftydmt

inche~

feetyardsmiles

? .­~..)

300.91.6

centimeterscentimetersmeterskliometers

in:!ft2

ydZ

miz

square i'nchessquare feetsq'uare yards,

square ~iles

acres

6.5 ~quare centimeters0.09 square meters0.8 square meters2.6 square kilometers0.4 hectares

enl­

mm2

km':ha

ozIII

ouncespotind~

short tons(2000 lb)

\1:\SS (weir:ht)28 granls

0.45 ,kilograms0.9 metric ton

tspTbspin J

aozcptqtgalft J

vd 3

teaspoons 5 rndlilitersI table~poons 15 millilIterscubic inches 16 millilitersAuid ounces 30 01 i II il i terscups 0.24- litersPl~ts O.~7 litersquarts 0.95 litersgallons .3.8 literscubic feet 0.03 cubIc me!er~

cubic yards 0.76 cu!)ic meter~

dpgrees .'" 9 {:} ft~r de~ree~

Fahrenheit :;ul,tra('tin~ (~ei~iu~

,321

v

mI.mL'mLInL

LLLLm'l

m'

vi

1 ~

1""E CFF'E(:l~ ()F SlfRFA(:E (:()ATIN(;S ()N THE

FA1")(;IJE STREN(;TII ()F Al..UMINlJM ALl..()YS

1. Statement of the Problem" Alunlinum is a widely ~J8ed metal in military ap·

pli('ation~ ~u('h a~ Vt·hi('lt~~" hrid~f'8" ai~U8hi()n vf'hicles" eh~." but its use is limited toan~a~ wh!·rt' thf' alunlinunl alh}}ls would not h~ under load with variahle or' ~on8tant

~trt~'~~.'~ and to Hrf'a~ when· lhf're would h{~ almost no severe ahrasion or corrosion. Anodic

('oatil)~~ h'nd to inc'n'aStJl the ahrasio!l and corrosion' re~i8tRn('f' of aluminum and its

aJlo~'~~ hut thcll c()atill~s have a detrinlental f'ffe.'t on the fati~ue f'n(Juranee (in ~ome in­

~tall ..t~~ h~' H~ nluf'h 38 fi5 perrellt). ThtJo ohjPc,tive of this work was to prnvi,de a 8urfac'e ,

In'atnlPfll 'and/or ('oalin~s that will allow thp USf' of aJunlinunt wrou~ht alloys in any t)'ptJoof pnvironnu'nl and that wil' hp ahle to with8tand the effe(·ts of ahra8ion and 8tre~8 ('orro·

~ion and h'JHJH'rat'unll ('han~e8 up to :l44P- ~ with an incrflla~d fatigue fllnduran('e.

2. 8a(·k~round. Thfll favorahle weight-to-volunle' ratio" ease of fabrication.a\ailahility 'if' a wicJt~ ,:arifJl~Y of pxtrtult'rl and other formlil" and easily applied wear- and

f~orro~ion-rf'~i.. tant anodic coating~ "lakfll alunlinunl a highly desirah~e en~in~ering

Jnalt'ri(~1 f..r nlan~' appli('a.ion~. ()ne g,·rious 8hortc~)!,lin~ of the use of hard ano..-Jized

c()atin~~ nn alurninun~' i:o\ that the eleetrolyti(" anodizin~ process may render certain of thealloy~ uU1'\uitahlt· for U8e a8 ~tru('tural nlemhers by dr'asti('ally 'redu('in~ ,the fati~ue

~tn'ngth (in ~(Hnfll in~tan(,f:llS hy a8 much as 65 percent)., Numerous references in the

lilf'raturp indic"at~ ~hat ar1()(Jic ('()'atings are ~ietrimental to fati~ue properties of highly

~tff·~~ed spfllcimenl". Although the exact nature of fatigue failure has not been elucidatedfull~" fhp .'on8fllnSU8 i~ 'that 'it may occur heca'lsf' of stress concentration at the micro­

crac'ks in the ('oatin~. Under repetitive applied )()ads" the- hasie metal loses its plasticity"rt~suhing in the pr()pa~ati()n ef (he local crack and reducing the cross ~ctional areas until

finally the appliflld ~tre8S exc~eds the- 8tatir 8tren~h 'and causes failure. There is som~

f·\rid~nce 'in .th~ literature l that certain annd~zing processes will r~duce fati~u~,'enduranc(ll

to a' ~JnalltJlr degrefll than the conventional anodjzin~: therefore" a wide variety of ar .odie('oatin~~, Wf1re studif~d. A ~u('('pssftll 8urfaee treatment prior to 'an()dizin~ wa~ s~turation

shc,t p~fllning p,f~r \filirary' Sp~('ifi('alinn MIL-S-l3] 65. The p~ening action acts to impart a

la~'pr of (~olnp.rf·ssi\'f' st,rf'S~f~8 on thfll 8urfac(ll" thpffllfore- increa!'\in~ fati~ue life .. decn-asing

~trf'~S ('or~o~ion.. and f'nhaJ1('i~l~ surfa("e !'trength.2

S. Wernick and R.- Pinner. Surface Treatment o'f Aluminum, 4th Edition (1972).

Metal f- i:lishin~ C;uidebook Directory. Metals and 'Plastic Publicatio~. p. 90 (1981).

~hot pt~enin~3 is alfi\o ufi\f~d to rpducf' ~urfacp tt'nsih- strf'~Sf>S in nl~taJ parts (such a~

axlp~, ~prin~8 (h~llral .. to~ional .. and leaf)...~ear~, ~haflin~. ain'raft ali~htin~ gt~ar' and~tnictural parts, ptc.) which are ~uhjt'('tt'd to re-pt>aled appli('ati()n~ of ('on)plt~x load pat­terns for the' purpo~ (}fin'pr()vin~ rt'~i~tanct'. to fati~ut' and ~tres1o\ corr()~ion cracking.

Shot pe(1'nin~ is al~o ufi\t'il for appli('ationli\ 1'\tu·h 310\ ('Io~in~ poro!'\ity in ('a~tin~f\ and~trai~htenin~or form,in~ appli('ahlt> partfi\, hut for shot pt'f>nin~ to have- the d~sirt'd {'ffef'!.

·the ~pe('ified intensity and covera~e mt.lst he achit'ved· on critieal arr-a~ where hi~h-h'nsio~l

stresses or stress ran~es, art' nlost likely tv cause f~til!ut' or ~tn'ss-('()rr()!'\ion failur~~ in ~f>r­

vice. Actual t'xperiencf' with ~('rvicf' failurt's or fati~ue tt'~tl'\ nlaylw rt'(Iuirt'() to di!"i('o,"t>r or

confirm the location of such areas ~uhjt'ct to critieal strt'sfi\in~ as a rt'1'\ult of any ('onlbina­

tion of ~rvice.. desi~n .. and nlanufacturin~ conditions. Aluminum alloy!'\ llr'ed for thiswork wt'na 6061-T6 and 7075-T6.

II. EXPERI~EN'rAL PR()CEDURE

,3. Approach to the Problem. Commercially availahle surfaee treatnlents and

anodizin~ procesees were stirve)'ed for evaluation purposes with respect to (a) fati~ue ~n­

durance (25 ..000-1b/in~2 S stress S 35,OOO.lb/in. 2) .. (b) abrasion (wt'ar) resistanct~~

(c) degree of coatin~ porosity (copper sulfate t.est)" (d) re~i,stance to thermal stress (:344° ~~).

and (e) resi8tan~e to ~orrosi9n (!5alt-spray. test) of the unsealed ("oatin~s.

4. Selection·of the Best Surface Treatment and/or C~8tings. Aluminum allo~'s

6061-T6 and 7075-T6 were ,selected for this work becaus(' they are the ~lloy~. u~ed rnost

.by the mi,litary. Tht' aluminu~ alloys were prepared in the shape of 'fati~ue coupons llh

in. by 4 'in. by 1/8 in. and' abrat,ion resistance test panel~ 4 in. by 4 in. hy lIB in. Tht'y

were shot peened a!i\ specified by MIL-5-131658 a~d "were anodized by difft'rent pro­cesses. The treated specimens ~,rere subje('ted to these tests: abrasion resistance, fati~ue en- .

durance"and de~ree,of p~rosity.The tests were conducted before and afterthespet'inlenswere sllbmiued to the folJowinl!' tests: thermal stress '(344° F) and~alt-~pra)' resistanr~.

The. anodizin~ techniques uMed were: low-temperature anodizin~ (28° F to 32° For 48° F

to 52° F),,~ regular an()dlzin~ (70° F),,· pulse an()dizin~ (55°F + 2°)~ Sanford low'"yohage anodizin~ (40° F to 50° F).,5 and integral color anodizin~(lCA-[)uranodi('300)5

'at 70° F..The anodized specimens were not sealed in order to permit evaluation of the-porosit), (Jf the coatings and their resistRnce to cor.ro~ion. lUI of these an()dizin~ proce~se~

have a deleterious effect o. the fatigue life of the alun1inum alloys~ the fati~ue life isreduced from 300,,000 -:,ycles f9r t1ntre~ted alunlinum to ·as low as 95,,000 (')'l'les for'

:~gular anodizing at an appl~ed stres~ 'l'evel of 25..000 Ib/in.2 In order 1<; evaluate lht' t'f­feet of the combination of shot peenin~ and a variety of anodizing processes.. speeiluens

were shot peened with S-280 shot t'o sahlration (0.006 Alm~n) in accordance with )lilitar)f

3 '-Shot Pee~ng o.fMetal Parts:~ Military Specificatio'n MIL-5-13 165B.

4 uAn'odic Coatings of Aluminum and Aluminu~ Alloys," Mqitary Specification MIL-A-8625C.

5 rommerciaJ anodizing' proc~,.

~'H'c'ificatioflo 'liL-S-l:~16SB and Wt'n' anodizf'(f in ae('ordance with the ahovf'-mentioned

allodizih~ pro(·e!"~t'!". F~ti~Ut' ..oupon~ Wt'n' pn'pared in a('cordance with t~e in~truction~

fllanual 6 for ~pt'('inu'n :'Jo, J, (:oupon~ with ro~nHI and ~harp ed~i:-~ wpre included,in order

10' c'valuah' tht, ('fff'ct of tlu"' ('ra('k~ and their propa~ation at the oxide coatin~-metal inter­

fact'. Fati~tH> \'alue~ for tlu' I('~t (,oupOI1!oi w"'re ohtained at differen~ load~ (25,,000 Iblin. 2"

27.'I)()O Ib/in,1. ;10.000 Ih/in. 2• :tLSOH Ib/in. 2

• and 3S"O{)() Ih/in.:.!) by u!ilinr; Baldwin

l;nj\'('r~al \1o(!el SF-2 and Sate('6 \1()dt"l~ ~F-2(i-144 and ·145 fa:i~ue testin~ machine~.·

Tht' ahra~i()n (wear) re~istar)('("'" the thi{'kne!oi!"o. and tht, (·orro.!oiion re~i~tanee 0 of the

~Iw('inlen!"o Wt're,dt~ternlined in ac{'ordanc(' with \f.ilitary Specification MIL-A-8625C.·l'he re~HIt~ ohtaifu·d from the difft'rent h'~t~ (fati~u{' endurance. abrasion resistance., and

dt'~re(' of por()~.~ly).an' ~hown in Tahle~ 1 and 2.

rrhf' ~4'annin~ t'leetron nlicro!'wopt' (~E~t) \\'a~ IIse{) at ~everal nla~nificationc) in

order to obser'O(,tht, ('(fr'(', (~f ~h()t pet'nin~ and ~t'veral anodizin~ pro('es!oie~on the surfaces, of tilt· alt·.nlinufn alloy~. rrh.· oL~t'rvation~ (Figur~s 1 through 9) were made· hefore flnd

after the aUo~'~ had h~en It·~tf(f for fati~ue endurance. thermal stress., and resistance to., ('orro~ion. All rni('ro~_ 3phs u~ed throughout thi!'\ report \\'ere tak(~n al lOOX ma~nification

and art' rt'pn'!"o('ntativt:, of the allo~·~. ~:;hol peening. and .iifferent anodizing processes u8ed~

for· pra(,tical purpo~t'~. no visual di,fferenees could he found hetween the differe~t

('o(~tings Iwfore and ~ftt'r each ~est ..

III. DISCUSS[()N

,,~. Result~. Tht' value!oi obtained before· and after tht-·exposure of the coated samples

to lht, ~~It-~pra~' te~t (336 hO,urs) apd too a temperature of 344 0 F (20 ho,:!rs) .with respect tofati~ut' ('ndunifH·t'. ahrasion resistan(>e., and degree of porosity were within the allowed~tatisti.('al deviation. An exanlinatiol1 of the lahoratory data mention~d above indicates

that an~' anodic ('oatin~ has detrinlental effeet~ to the fati~ue endurance of aluminum.Tht:, data also ·indiea~~ that the f'(~nihinationof inte~ral color anodizinf.Y, (leA) or hard coat

'fIL·A~H62SC.Type III with ~aturati()n !'ihot p~enin~ per 1\filitaOry Specification MIL-S­

1:316SB havr a henefi('iar e.ffect on the fati~ue endurance of aluminum alloys 6061-T6and 7075-.i~6 fati~ue ('oupons with round and sharp ed~es. In addition, by imparting a('ornpre~!oiive ~l1rfa('e ~tre~·gth. a ~reater ~tr~ss load is nteded to fracture the coupon. The

data al~o i'Hfi('ate .that (,{)UpOI1"!'i with ~harp ed~es flo not have a fati~ue life as lon~·as the

('oup()n~ with r(}uncfeded~es" prnbahlyheeause of the many cracks or imperfections of the

pcf~t,~ pre!'ienl in the ,cornier ('OUPOIlS: ther~fore~ sharp ~d~es should be finished or rounded

hy shot pt~eni~l~ or ~andblaslin~ in order to dimini!oihthe JW~;sibili'ty of crack propagation.

4 HAnodic Coatin·gs for Aluminum and Aluminum Alloys," Military Specification MIL-A-8625C.

(, Satec Systems, Inc.~"Grove City, PA ~6127.

3

Porosity Test··

SurfaceTreatment

None

. Thickness(mils)

NjA

Table I. Aluminum Alloy 6061-T6

Fatigue Endurance Abrasion Resistance(Kilocycles) Unsealed Coatings

Coupons With Weight Loss UnsealeJ COdtings Heated for 20 h Salt-Spray TestRound Edges Sharp Edge~ (nlg/ 10,000r) as Received (a 344° F i~Ln~~~~!~~'!tl~~

(a)300-400 (a)200-300 N!A N/A N/A Ligilt

(b) 200-300

All anodizing 0.8-1.5 (a) 50-250 (a) 50-100 15-25 Not tested Not tested Not testedprocesses w/0shot peening

Shot peening ~nd 1.0 .(a) 7909 (a) 874 17.8 . Light popul~tion Light Light corrosionintegral· color (b) 100-300 populationanodizing (lCA)

~

~hot peening (a) 520 Light population Light Moderate corrosion0.9 (a) 369. 16.8MIL-A-8625 " . (b) 100-300 population

.. Type II

Shot peening and 1.5 (a) 2405· (a) 436 18.0 Light population Light Light corrosion.MlL-A-8625 . (b) 100-300- populationType III

Shot peening 1.5 (a) J591· (a) 312 20.4 Negligible Ne'gligibIe Ught corrosiOl.anodized hard (b) 100-300coat (AHC)duplex coating

(a) 25,000 lb/in.2 .

(b) 30,000 Ib/ir.-1

·Sample did not fail

··Density of the metamc COP~l sPecks on the test site (visual inq>ection) - the heavier the density (population). the greater the porosity ~

Table 2~ Alurninu~ Allor 7075-T6'

Unsealed Coatings· Heated fOf 20 has RCl'cived '- (a 344° -F

SurfaceTreatrnent

None

Thickness(rnns)

N/A

Fatigue Endurance(Kilocycles)

Coupons \\'ithRaund Edges Si12rp Edges

(a) 300-400 (a) 200-300(b) 200-300(c) 500-600(d) 50-70

Abrasion ResistanceUnsealed Coatings

Weight Loss(nlg/ 10\000 c)

N/A N/A N/A

POfositv Test··

Salt -5 pray Test(Unsealed Coatings)

Light

All ;lnodizingprocesses wloshot peening

0.8-1.5 (a) 50-100 (a) 40-50(h) 30-50 -

(r) 20-30(d) 15.-20

10-25 Light po pulation Light

population

Not tested**

Ul

Shot peening and 1.0-integral coloranodizing.(ICA) .

(a) 14845(b) 1951(c) 1276(d) 1072 ­(e) 144

(-a) 213(b) 239(c) 381(d) 243(el81

24.0 Light population Hvypopulation

Moderate corrosion

Shot peening and 0.9MIL-A-8625Type II

Shot peening and ] .5MIL-A-8625Type}1I

Not tested

(a) 1500

Not tested

(a) 360

20.0

19.1

Light population

Moderatepopula~ion

Hrypopulation.

~toderate

population

Not tested***

Not test.ed***

Shot peening and 1.5 (c) 1312* (a) 1666- 119.9 Light population Light _ Not tested*~*

anodized hard (b) 248 pGfuJationcoat (ABC) (c) 237duplex coating (d) 102

(a) 25,000 Ibfin. 2

(b) 27,500 Ibfin. 1

(c) 30,001) 1b/in. 1

(d) 32,500 Ibfin. 1

. - (e) 35.,000 Ib/in. 1

~ Sample did not fail. .*. Density of the m~tallic copper specks on the test site (visual inspection) - the heavier the density (population), the greater the po!"osity."'·*Proccssed Coupons Not Available

Figure ·1 .. Untreated top s!-,rface.

The· surface is uriform with· some imperfections. Because of the uniformity,

once a cr~ck 1S initiated it grows and propagate-s' untH there is a fracture.

r igure 2. Shot-peened top surface.

Shot peening distorts thf) surface, impeding or slowing the growth and propa­

gati~n of a crJck.

Figure 3. Anodized-unsealed top surface.Anodic coatings tend to emphasize the surface defects. and· ir:nperfections ac­celerating crack growth and its propagation until fracture occurs.

"

\~-

, '.~,' ..-.. (

Figure 4. Shot-peened and anodized-unsealed top surface.The top anodic coating layer evens out the d~formation (visual appearance)'produced by the shot peening. The main purpose 'for anodizing a shot-peenedsurface is to increase the corrosion and abrasion resistance of the shot-peenedsurface so as to retain the increased fatigue endurance.

7

Figure 5. Shot-peened and anodiled:"unseah.~coating heated to 3.+40 F(20 hours) and 8XpoS...td' to salt-spray test (336 hours).

When anodic coatings are ~eated, they craze. The corrosion .of the alloy seernsto initiate' at the intersection of the microcracks which' grow and, propi'lgateuntil the substrate fails.

8

I I

r~gure 8. Shot-peened surface w'th an unsealed anodic coating-f.racture ofthe coopon (vibrating ~nd).

The. same comments for figures 6 and 7- apply to Figure 8. The wear pattern of

the fracture indicates horizontal and ~ertical vibrations.

Figure 9. Unsealed anorl'c.coat,'ng-fracture of the coupon (vibrat,ng end).

The same cornrnents for Figure 6 and 1 apply to Figure~. The flGges o.n the

Inlt'al areas of propagat,on were caused PV imperfections on the stationary

end rubbing. into the vibrat,ng end.

II

\11 additior.al anal~'~i~ of thf~ data in(iicat~!'4'that alHHjjzin~ pt"t \1IL.. A-H625C

T~ /W II ... ho.lIld Iw a"oid.·d iJ ItH'~Jw.'iIJIf~n i~ f!oin/{ to 1..·1> und~~ !'itr~~~ It~('au~~ thi~ (iJHuliz­

ifl~ prew.·...... It'nd~ :q df'.'r~a~t' dra~ti4'all~' thfl> h{'rlt~fif'ial f·ff~(·t~ of ~hn' pt'fl>nin~. 'flu' '(,o'rn­

,.ft·...... ;\.· la~.·r irnpartfl>fl ~.~' th.. !'ihi)t' p~fl>nin~ prn(~~~!" will providf' an ir)('r~a~~{1 fatif!tJt' liff',

11111 Iht· la~'f'r",ill IO!"flO itl" f--fft'4'ti"flO rU""'''' in a corro",ivt, t'nvir(.nnlflOnl and in, ('ontaf't withdi ...... irnilar flu-tal!" h~('au!"f~ thp ('ornpn'~",iv~ layt·r 'd()f~~ not havfl> any (~()rro~ion rfl>~i!".an('t·

propc·rtic·~. ~fIH~ pUrp()~f' of Itu' iUloflizin~ a!" a !'iup~rfi('ial )aYfl>~ OVtl>r thflO ~hot rWf»r.in~ i~ 'to

prott·c'. rlJ" ('o.nprfl>",,,,i,,.-- la~'t'r in a ('orro~ivflO t'nvironfllflOnl aruJ to providf» an ahra!"ion-

n· ... i lant {·oatin~. ~hot p~f'nin~ iUf'n'al'ifOl'i th~ fati~utlO·lj.ft·, dirninil'ihflOl'i thflO p()l'il'iihilit~ t.f

.. 'n· ·orro!'iion c'rackiflf! in ... tI~(·t'J)tihl ... C:.lllo~·~" and irH'nlla!W~ thfll !'iurfaef" ...trpn~th: dUll

~lf.ocli.' c'oatin~ inc'n'a"'f~'" Ih.' w.'ar and ('orro~i()n rt· ... iio\tan('f~ (thf~ ('oalin~, ('oulff hf' ~f'alfld

,'itJ.lO·r ~ ith T.·flon or a cluplc'x ..~al or'a luhrif'iH10. Tht' cornhination of t.H~ ~h()"IH't'nin~

aucillu' anodic' ('oatin~{lC:\ or T~Jw HI ~ will allow thf" til"fll of alunlinurn and il!'l alloy!- in

tHan~ f'n' irorHn.·nt~ for applif'ation~ ",·hfllrt· it ('ould not hflO U1"flO(tprt"\'iou~I~'. A worclof

f'(lutiou \\ i'h n'io\Jwct to io\hcH p~t'nin~:·lh.' p~t'nin~ of \'~ry thin or ~nlalllo\f~C'tion~ to hig-h in­If·n ... il·it·~ ... hould hf ' (I\oidf·d ht'C'«lU:->f' of.ttH~ di ... tortion and hi~h-·rt~~Cfhlal h'n ... ilt, ... tn· ......f· ... in

tht' ('ort· fnaftarial that fna\' rt~ ... uh frorn ~'H'h p.'f~ninf!. Thi ... i~ partif'tlfarl~' tnlt· wlwn thf'part ha~ ~lIrfaC'f'''' ·fini .. lu,et afh'r h~at In'atnu'nt oriio\ lI ...t'd 3!" a h'n~ion .flJf'rnhtlOr.

·a~ 'rhf"C'nrnhinatiof1 of ...aturation· ... hot pflOf"nin~ pflOr \Iilita,:,' SpflOeifi('ation 'fIL-S­I:J 16.1 and inltlO~ral ('o'lor anc)(jjzin~ (f( :A·Dt1ranfHJi(':~O() prn('fl>~~) or \1 IL..A-8625'1,\p~III. will rt· ... ult in ahuninurn with all anodic ('()aliJ1~ that hal" ineff'a~ed 'fati~u~ f"ndUrarH·.~.

i ... If· ...... "''''''.'t·ptihlta to Io\trf"~~ ('orr~)",inn ('ra('kin~_ 'arui ha~ 'f'uhanceo· surfacflO ~trflOn~th. 'fhfll

ahu\·t·-nlf'!Jtionf'd ~urfaf't.. trf"atrllf"rtt will allow th~ Ul'it1> of aluminunl wr()u~ht alJoy!ol in ~Hl~'

ty p.' of f'u\'ironuJf"nt and he ahl~ to IwUpr wtth~tarHj tht1> t'fff'f·t~ of ahrasion and !oItr(1l~!"i(·()r·

ro... ion .. 'h'rnJ)flOratur~ ('han~f'~ up to :l·~t.. , F with an inerpa!olflOd fati~!lflO flOndl.rar1(·~.

b. Tht· leA hard ('oar prut'f"!"!" win hflO ('n~t f'fff"(,tiv~ whf'n conlparflld to ,Ih~ .1~yp~ IIIc..oalin~lwc·au!'~ tht· fonnf"r i!ol a 700 F prc)C'~~!". nl~(Hlwhilf'_ thflO Typfll Il~ pro"f'~~ rflOfluin'!ol

j~)W h'rnJwraturt' t2R O to :l2° F orJ.8° In S2° F).

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BIBLI'~GRAPHY

Beitel. (;. A. and. C. Bowles~ "lntlucnCt~ of Anodic Layers on Fatigue-erack Initiationin Alurninuln, " ,1letaJ Science Journal, pp. ~5-91 (-1971).

Bo\vcrs, J. E. and N. J. Finch, HThe Fatigue Behavior of Bolted Joints in an Alunli-THun 5\ 2('; Zinc. ~1agnesiuln 11/{k Copper Alloy," Journal of theInstitu/e ofJ/c/uls. pp, 239-244 ( 1(72).

Frishee. L. r .. "The Lockheed Tfi StarJournal, pp. ~3Xq-402 (ScI" 74L

An Operational Overview," Aeronautical

Harris. F. and S. Levine. "Devcloprnent or- a Continuous Hard Anodized AluminumSurf:.l(:e," Us :\flny "1ohilltY Lquipment Re~earch and Development CommandReport, No. J.q 52 (~1ay ()9),

Larsson, \. and L. Jarfal!. "1:atJ~t1e Tests with TunneL Notched Specimens of ForgedAltllninurn 3h33-4 ot Various Surfal'e Treatments,H The Aeronautical ~esearch

Institute of S\\'t'den.rechnical Note. Fr~'A BU-l 729.

\1u:-phy. ~1., HTel'hnical Devcloprnents in 1979 (Inorganic Metallic Finishes, Processes,Jnd Lquiplllcnt). " .He/a! Finishing. p. 21 (Feb 80).

\\'oot!. J. R.. HSurfacc ~'flects of the StressCorrosion ~f 7075-T6 Aluminum Alloy,"('urYf..'n/·t:'llRilicerillg Practices. pp. 20-27 ( ]~7l).

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