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NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS-, -.

Walmm luIIBolrl’ORIGINALLY ISSUED

Augwt 1943 aeRestricted Bulletin 3E23

THE EFFECT OF ARTIFICIAL AGING (X THE

TENSILE PROPERTIES OF ALCIAD 24s-T

AND 24s-T ALIJMJIWMAILOY

By Joseph N. Kotanchik, Walter Woods, andGeorge W. Zender

Langley Memorial Aeronautical LaboratoryLangley Field, Va.

,N’ACA.’””,,..WASHINGTON

/-

NACA WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution ofadvance research results to an authorized group requiring them for the war effort. They were pre-viously held under a security status but are now unclassified. Some of these reports were not tech-nically edited. All have been reproduced without change in order to expedite general distribution.

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3 1176 01364 9844

NATIONAL ADVISORY OOMilITTD FOR AEnONAUTICS

RBSTRICTZD WLL.IT IB

THE EFFECT OF ARTIFIOIAL AGING OIt TIlE

TUSILE PROP3RTIBS OF ALCLAD 24S-T

AND 24S-T ALIDlI'}JID! ALLOY

By Joseph N. Kotanohik. Walter ~oods.

and George W. Zender

An experimental study was made to determine the effeot of arti­fioial egl~g on the tensile properties of alclad 24S-T and 24S-Taluminum-alloy sheet material. The results of the tests show thatoertain oornbinationc of a~ing time and temperature oause a markedincrease in tILe ~'ield strength and a smaL], increase in the ultimateRtrength; these incr~Qces are accompanied by a very large deoreasein elongation.

A ourve is presented that shows the maximum yield strenfths thatC6.:1 be obtainud by ngine; thif: material at various oombinations of timeand tamper6.ture. The higher valu~s of ~ield stress are obtained inJIlt.tt,~rio.l aged at relatively lonGer times and lowor tomperl1turos.

INl'RODUm'ION

In the design of an airplane. weirpt oontrol is a leading problem.Every part of the afrplane must be so designed or seleoted as to elimi­nate unneoessary weight.- One of the most important items that contri­bute to the gross weight of the airplane is the struoture. For this

.reason. th~ airplane strnoture is exam,inod most' oritioally for elimina­tion of unneoosShry weight. The oontinuing advanoes in methods ofanalysis are an important faotor fo~ bringing about a reduotion in weightof the airplane. but the airplane designdr and builder must. ib addition.utilize other methods for oombating th~ trend toward inoreased struo­tural weight. 6ne of the most direot ml!thods is to improve the strengthprop~rties of matarials already available or in ourrent produotion.This method has the very important advantage that it OBn be put.tnto usewith a minimum of d~lay and interruption to ostablished methods ofproduction.

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J!numbcm of airoraft oompanies.are now .oonaidarlngthe use of 24S-Taluminum alloy of whioh the strcngtinproportion have been improved byartificial aging. Thi~ report presents the results of tensile teats onalolad 24S-7’and 24S-T aluminum-alloy sheet material that has been artifi-aielly afod at variuus combinations of temperfitureand time.

UA7’ERIALlNJRARTII’IHALLY AGEO !I%STS~liCIM~-S

As the purpoce of these tests is to present tho results that oan beobtair.edby hrtif%ci=l cging of commercially ohtainahle material, specimens,of tho dinerisicnsshown in figure 1, ware out from sheets ~elecked Iromalclnd 2is-T and 24S-T aluminum alloy as receivetifrom the manufacturer.The stretchin~ aod rolling operations p~rformed on aluminum alloy at themills are approximately equivalent’.t~ the sold work done in giving the sheeta permanent elon~ation of 1 peroent (refersnce 1). The axtent to whiohthe strength propwt!es oi’245-T al’xninwialloy oan be improved by mti-ficial agin~;is dtipend<%nt.~i~ont!leAmount of cold ~~rk F~rfo~Jed on th~material prior t.ot%c aging prnoe~s (rcferenoe ~). It Is l-herefor~nc~es-sary thut the material be of uniform qu~lity P.Sregrrds t?e amo-mt of ooldwork performed prier to c.gir,gin or~er that conais;ent results be obtainedfrom the crtifioifilnging.

For thlJtests reported herein, the cuttin~ of tb.e24S-T and thealclad 24S-T specineus frain singl? she% of 9uoh material assuredun+.f.~r,nitj-of the specimens as re~srts the de~ree of oold work ?tirfornedupon them. That the material was unifonrtus regords 00Ic?work is in-dinated by the consistent trends es+wblished by the test data in ficures2 and 3. The extcnsivo adoption of the artifioi61 ~ging process wouldnecessitate that C1OSC rwylotian L= nuqintaincdoc the uniformity of andtho amonnt of cold wrk porforrmd oa thn aluminun alloy.

The test apocimcns VW-O fitcuipodfrom sinlqleshedts of 0.064-inchalclad 24S-T and 243-T uluad.rIwnalloy by nouns of a die. In the toctportion of the spcci.ncn,tt.eshear~:ded[;eswere ci?rofullyhaad filed toremove tnc+sli~kltlyt“~rnoded~e left by *h~ stsmpin~ die. One sFecimcnwas made for eaoh combination of tino nNd tenpersture investi~tcd.

-4rtificiclcging of the speoimens was rerformed in an elcotricallyheated air furrwce, and the speoimens were cooled in air at room tempsra-turc. The test s~eo!.mansvcrc plaa.:din tho furnaop, whioh was atths dnsirod temperature, and the aging time wzs “takenas the e~tire

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period during whloh eaoh speolmen was in the furnaoe. Theresulte are therefore representative of the values obtained. .with-material that h artificially aged.in thissame manner.. ..

The data for tho tensile 8treaa-atraln ourve were obtained for

* eaoh epeoimen to a value of etrain beyond that at the 0.2-peroent-of’factyield strength. Straina were meaeured by two Tuokerman optioal

2atrain gagea of 2-inoh”gage length attaohed to opposite aides of theteat apeoimen. The elonga’tlonat failure was determined ~ meaauring,after failurme,the inoreaae in length of the initial 2-inoh gage lengthof the.teat speoimen to the neareat 0.01 Inoh.

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TE3T RHTILTS AND DISCUSSION

The results of the tcnaile tests on the artificially aged teatapuolaona are given in figures 2 to 5.

Fi&ure. 2 chows the variation in the ultimete strength, the ylaldatrungth, and the olonc~tion of alclad 24S-T mat~rial that ia sub-jeoted to artificial aging for psriods of 2, 4, 6, 7, and 10 houra attemperature th~t vary from 100° to G~OO F. The hnportant informationcontained in this figure ia that a eubsthntlal increase in yield strengthend decrecse in elanqr)tionocsur in t},ematerial when aged in thetemperature range of 3400 to 400° F. In this temperature range, asmall increase in the ultimute strength of the materiel alao oocura. ..

The most decircble rcault obteincd from artificial aging ia thelar~e increase IR yie16 strength. Although this report preaentaonly the results of tensile teata, some oomprcasion teata have been per-forrmd on artificially eged material and these tests indioated thatthe oompreasive yield strength was Inoreascd in essentially the sameway aa the tcn8ila yield strength. By taking into Eocount the inoreaaein yield strength, the airplcne designer can eff’cotsubstantial reduo-tiona of wei~t in oertain parta of the airplane. For example, thefull inorease in yield strength oan bo utilized in the design of oom-preaaion members ao proportioned and eupported that they will not failby inatabllity befora the compreaaiva yield strength ia reaohed. Inthe caae of t.?naionmenbera, only a part of tho inoreaae in yield ..

etrength oan bc utilized und~r prssent design roquireneats beoauae theserequirmenta specify a definite ratio of allowable yield stress toultimate atresa, and the ulttiate strength of the artificially agedmaterial La not inoreaaed in the name proportion aa ie the yield strength.

The inorease in yield strength ia aooompanied by a change in theelongation in 2 Inohes from about 1S pciroentto about 6 pcroent. Thisdeoreaae in elongation will undoubtedly add to tho difficulty of

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forming the material during fabrication. In many oaae8, however, the . .added difficulty can be avoided ~ completing the forming o?eratiomprior to artificial ag~ng.

Figure 2 also ~hotm that for any aging the the temperature must“be~in~ined within,a rauge of ‘5°Fof the optimum value in orderthat the best increase of yield strength may be obtained. This8tandard af temperature maintcmanoe ia readily attain~blo with modernheat-treating equipment.

The v~riction in ‘yieldstrmgth of alolmi 245-T material that issubjected to artificial aging at cot?stanttemperatures for varyingperio23 of time is shown in figure 3. It will be noted on this figurethat for velaes of tcmpcmaturc almvc 350° 1?there is an aging time “whioh will result in a mximum i~orease of yield strenglin. For sgingtimes less then or grenter thqn the optimum tine, lower vtilucsof yie?tistress will be o>+mined. .#ttem~..m~turosin exeess of 4250 F, th~.aging tim5 bcocxnnrvery cr~-tical. The danger of undera~ing or ovcr-aging of the mcterial with consequent lerge iecrease of yield strength “is quit~ swiousm For this re~eon, ilgiUFtemperuture6 in exorss of425° F are not f?a8i’blzfor production vhcre t% character of ths workis ehenEin&”and whers it is difficult to detsrmi.net!!e”exacttime atwhloh the maturial reaches K?!eaging”temperature. At eging temperaturesof 400° F and lower, two inpo?tant advantips exist; namciy, higherabsolute valu~s of yield s-tren~thocn be oht~inad and thzre is e consider-able range of time at w}linhnging nay be tmninated without appreciableloss of yield strem~ch by reason cf small amounts of underaging Qroveragingm

Figure 4 presents n ourve of yield-strengthmaximums for various “combinations of’thus!end tumperatur.’?.Within the range ~f valuesoovered by this hvr~GtiSetion, this-curve shows that, as aging tempera-ture decreaaes, the agin~ time required for oest yi~ld strength increases.The curve ~lso shows that the higher valuee of yield strength.are obtainedat the combinations of lower temperatures and longer aging times shownon this figure.

Figura 5 shows the variation of the tensile properties of 24s-Twith te.nperaturefor a conetant aging time of 2 hours. When figure 5is oi)mparedwith figure 2, it is evident that 24s-T material responde .to artificial nging fn a manner simil~r to alclad 24S-T.

The test epeoimens which were a~ed for 5 hours et various tampor-aturea are shown after fraoture in figure 6. The change in elongationis olearly se%n In the final lengths of th~ speoimans. The ohnracter-iatic freotures thet occurred tit*he various temperatures for esch agingtime are also shown. At temperatures below the range of cmit$cel aging ,temperatures, as in the 100° F and 200° F specimens on figure 6, the

fracture was normal to the direction of th~ load but wasat 45° to the thickness of the material. In and beyond

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inclinedthe region

of temperatures corresponding to the greatest decrease o,felongation,temperat’%resof 370° F and nigher, the fracture changed to one that wasinclined at 30° to tinewidtilof the specimen. The surface of t!lefracture V:RSrelatively smooth for the material aged below the critical

~ temperatures but it became verjrroug!land irregular in the specimensy ,

agec~at the hiighertemperatures. In the transition range of tempera-A tures, the frecture was partly of both types as shown by the specimens

markzd 3~0° F’and 359° F’in figure 6.

STRESS-STRAIN ~JRV2S

The tensile stress-strain ourves for the specimens tested areshown in figures 7 to 12. The O.Z-percent-of’l’setyield strength isindicated on eac’hstrzss-strai~ curve by a short inkercept line. Theseyield strengths were used in preparing figiires2 to 5. The stress-strain curves Shovi ths.t the modulus of eh?sticity is substantially thesa:nefor the co.mhinationsof tempera”bizreand time included in this in-vestigation. It can Le cbservtid,howvcr, that cs the cging tempera-ture ilicrcases the initial part oi’the stress-strain curve tends to de-velop more curvature, which indicates a trend toward reduction of theproportional liiiitet the higher ~giilgtemperatures.

C0NCLUSIOR3

Artifioiel aging of alclad 24S-T alwninum-alloy,sheetmaterial in“the es-receivetifionditionproduces a substantial increase in yielcistrength, a small ilicreascin ultimate strength, emd a large decrease inelongation.

The artificial-aging process prodwec essentie.llythe same effecton 24S-T sheet ma.tcwialus on alclad 24S-T sheet material.

At any ~iven temperature there is an optimum value of aging time re-quired to obtain maximum value of yield strength. In general, the agingtime required to achieve maximum yield strength becomes less as thetemperature increases.

The range of aCin& temperatures for which a substantial increase inthe yield strength is noted is small.

Lan&ley “Mcunorial~.~ronautic~lLabar&tory,National Advisory Committee for }.eronautics,

Langley field, Vai,

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REFZRWCE

1. Mozley, Paul ?.: Elevated Temperature Aging of 24S Alumin*umAlloy.Paper presented at the eleventh an,nualmeeting of tineInst. Aero.Sci., Jcin.1943.

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EBOfansa (etafl) I /f-g-/o-i<> Kotanchik. J. N. IDmslON: Kstoriala (8) Woods, Walter (SECTION, Aluminum and Alloys (10) Zender, G. W. (CROSS REFERENCES, Aluminum alloys - Aging (10575.5)

AUTHOiMS)

ATQ^BBa ODIG. AGENCY NUMBER

RB-3IE3

REVISION

FORG'N. TITLE,

The effect of artificial aging on the tonsils properties of alolad 2i^-T and 2liS-T aluminum alloy

ORIGINATING AGENCY: National Advisory Committee for Aeronautics, Washington,

TRANSLATION, FEATURES

diagrs, graphs COUNTRY

U.S. LANGUAGE I

Eng. ' =ORG'NX;USS U. SJCUSS.

Unc lass. DATE

Aug'k? PAGES

18 IUUS. 12 photos

AESTBACT Investigation to determine the effect of artificial aging on the tensile properties

of aided 2I4S-T and 2I4S-T aluminum-alloy sheet material. Results of the tests indicate that certain combinations of aging time and temperature cause a marked increase in the yield strength and s small increase in the ultimate strength. Both of the increases are accomplished by a very large decrease in elongation. Higher values of yield strength are obtained in material sged at relatively longer times and lower temperetures.

NOTEi Requests for copies of this report must be addressed toi N.A.G.A., Washington

T-2, HO, AIR MATERIEL COMMAND AlR TECHNICAL ONDEX WRIGHT FIELD. OHIO, USAAF vmo-ai HAH 0 ea