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Formygrandchildren,AlexandreVargel,RomainVargel,AlexandraBourgoin, andLaureBourgoin

Foreword

Ifthereisametalofthefuture,itisaluminium.

Aluminium’ssuccesshasbeenconsistentforover100years.Mostrecently,atthestartofthe21st century,annualconsumptionofaluminiumreached29millionmetrictons;by2017,thatﬁgurehad risento80millionmetrictons.Andsomearepredictingconsumptioncouldreachabout120million metrictonsin2030.

Thisishardlyasurprise.Aluminium’sintrinsicpropertiesmakeitauniqueandextremelyvirtuous materialthatrespondstonumerouschallengesinoursocietylinkedtoclimatechangeandresponsible managementandprotectionoftheEarth’sresources.Aluminium’sabilitytobeendlesslyrecyclable withoutlosingitsinitialpropertiesisanexcellentexampleofthis.

Furthermore,thankstoitslightweightcapability,aluminiumallowstransportationvehiclesonland, intheairandatseatosigniﬁcantlydecreasefuelconsumptionandthusdrasticallyreduceemissionsof greenhousegases.Italsocombinesductilityandahighlevelofresistancetobothimpactsand corrosion.

Beyonditsspeciﬁcproperties,theinexorablefascinationwithaluminiumisﬁrstandforemostthe resultofdecadesofresearchandinnovation.Generationsofresearchershaveworkedonthedevelopmentofincreasinglyadvancedalloysandever-moreinnovativemanufacturingprocesses.

Thisisparticularlythecasewiththetechniqueoffrictionstirwelding,whichmakesitpossibleto assembledifferentmaterialswithouttheneedforrivetsoradditivemanufacturingprocesses,also knownas3Dprinting.

AtConstellium asuccessorofthePechiney,AlcanandAlusuissegroupsandagloballeaderin innovative,highvalue-addedaluminiumsolutions wemakesureengineersandtechniciansinour R&Dcentrehaveaccesstothemostsophisticatedresourcesandmethodsavailable.Thanksto manyclosecollaborativeprojectswithourcustomersandnumerouslaboratoriesanduniversities worldwide,ConstelliumhasdesigneduniqueandrevolutionarysolutionssuchasAirwarefortheaerospacesector,SecuralexandHSA6fortheautomotiveindustryandAeralforaerosolpackaging.

Althoughtheyareusedindifferentapplicationsandcomefromawiderangeoffamiliesofalloys, thesenewproductshighlightourindustry’squestforexcellenceandourabilitytoimaginetheworldof thefuturethroughcontinuousoptimizationofthepropertiesofaluminium.

Oneofthefundamentalareasofresearchiscorrosion,thesubjectofthisbook.Althoughitis naturallyresistant,aluminiumneedstoofferever-higherperformance.ThisneweditionofChristian Vargel’sbook, CorrosionofAluminium,reﬂectstheknowledgehehasaccumulatedoverhis40yearsat Pechineyasanengineerinourresearchcentre.Asaspeakerandauthorofseveralbooksonthemetal, ChristianVargelisarecognizedexpertintheﬁeldofaluminiumcorrosion,orashewouldputit,a corrosionpractitioner.

Thankstoitsscientiﬁcapproachtothetopic,thisbookisbothanexplorationofthephenomenonof aluminiumcorrosionandapracticalguidetotheuseofaluminiumalloysbasedontheircorrosion properties.Aimedatbothacademicsandprofessionals,itisunrivalledinitsﬁeldandIwouldlike tooffertheauthormywarmestthanksforentrustingitsforewordtome.

Jean-MarcGermain ChiefExecutiveOfﬁcer,Constellium

Forewordtotheoriginaledition

Withanannualconsumptionof25millionmetrictons,aluminiumisthesecondmostcommonlyused metalintheworldaftersteel.Itslightnessisveryoftenthemostimportantadvantageforthecommercialdevelopmentofaluminium,whichexplainswhyitisextensivelyusedforgroundtransport, aerospaceandshipbuilding.Thisisalsothereasonwhytheautomotiveindustryiscurrentlyveryinterestedinaluminium:lightnessisbecomingapriority.

Thesecondadvantageofaluminiumisitscorrosionresistance.Thisexplainsitsimportantposition inconstruction,civilengineering,transport,heatexchangersandsoon.

In1890,navalarchitectshadconsideredaluminiumforreducingweightinvessels.Butinorderfor aluminiumtobeuseableforshipbuilding,metallurgistsandcorrosionspecialistsinthe1930sﬁrsthad todevelopaluminiummagnesiumalloys.Thesealloyshaveanexcellentcorrosionresistanceinthe marineenvironment,andtheyareweldable.Since1960,allhigh-speedferrieshavebeenbuiltinthese alloys.

Asimilartrendwasobservedwithheatexchangers:aluminiumwasrecognizedasanobvioussolution,especiallyforautomotiveheatexchangerssince1970.Infact,severalalloyshaveverygoodthermal conductivityandexcellentresistancetoenginecoolants,makingitpossibletomanufactureheat exchangersthatarecheaperandofcourselighterthantraditionalheatexchangersincopperalloys.

Projectsfordevelopingrenewableenergysources(solar,etc.)haveoftenbeenbasedontheuseof aluminiumheatexchangersforseveralreasons:amuchlowercostthantitanium,goodthermal conductivityandexcellentcorrosionresistance.

ChristianVargel,throughouthislongcareerwithinPechiney,hasbeenapractitionerofaluminium corrosionandarecognizedexpertinthisﬁeld.Hisﬁrstbook, LeComportementdel’Aluminiumetde SesAlliages (TheBehaviorofAluminiumandItsAlloys),waspublishedbyDunodin1979.

Sincethen,hisexperiencehasgrownsteadily.Hehasfollowedmarineapplicationsandautomotive heatexchangersandhasparticipatedinmanydamageassessmentsinvolvingcorrosioninservice.He hasalsogivenmanytalksonthecorrosionresistanceofaluminium,andhascontributedtomanyof PechineyRhenalu’stechnicaldocumentsandbrochures,suchas‘AluminiumandtheSea’and ‘AluminiuminIndustrialVehicles’.Wethereforeencouragedhiminhisprojecttowriteasecond book:hisrecognizedexperienceintheﬁeldofaluminiumcorrosiondeservedtobemorewidelyknown anddisseminated.Thisbookwillcertainlycontributetomeetingthisgoal.

Corrosionisadifﬁculttopic.Iamdeeplyconvincedthatthepractitioner’sapproach,basedon expertiseandexperience,isbestforassessingthecorrosionresistanceofaluminium,anassessment thatisobviouslyoneofthemainconditionsforthedevelopmentofmanyusesofaluminiumin transportandconstructionpowertransmission.

ChristianVargel’sbookpresentsthereaderwithaglobalapproachtocorrosion,comprisingthe selectionofalloys,designprinciplesandserviceconditions.Iamconvincedthatitwillcontribute tothedevelopmentofaluminiuminthoseﬁeldswhereresistancetocorrosionisanessentialproperty.

BernardLegrand FormerDeputyChiefExecutiveOfﬁcer

Pechiney,September1998 xxxvii

Preface

MylongcareerinthePechineyGroupfrom1957to1997andsubsequentlyasanindependentconsultantprincipallyfocusedonaluminiumcorrosionhasenabledmetoacquireextensiveexperienceinthis ﬁeld.

Myexperienceisbasedonthetreatmentofthemanycasesofin-servicecorrosionthatIhavehadto dealwithoverthepast50years,andontheelectrochemicalandmetallurgicalfundamentalsof aluminiumcorrosion.

Thisdualapproachhasmademeacorrosionpractitioner,inthesensethatIhadtoﬁndanexplanationforcasesofcorrosioninserviceorthatIhadtoplanhowtoavoiditthroughthechoiceofalloys, operatingconditionsandsoon.

Indeed,corrosionremainsacomplexsubjectbecauseitdependsonmanyparameters,whichmakes itnecessarytohaveapracticalapproachtobeusefulandexplainableonthebasisoffundamentaldata.

Thisengineeringactivityhasallowedmetoacquirewideexperienceinaluminiumapplications, particularlywherethequestionofcorrosionresistanceofbuildings,heatexchangers,renewable energysystems(solar,OTEC,etc.),transport,shipbuildingandsoonisconcerned.

Ihavefrequentlysharedmyexperienceofaluminiumcorrosionatnumerousconferencesandin severalbrochurespublishedbyPechiney:“AluminiumandtheSea,”“AluminiumintheAutomotive Industry,”“AluminiuminIndustrialVehicles,”and“AluminiumSemi-ﬁnishedProducts.”

Followingarequestofthepublisher,Elsevier,Iresumedthereeditingoftheﬁrstversionof Corrosion ofAluminium publishedin2004,whichwasthetranslationof Corrosiondel’Aluminium publishedin FrenchbyDunodin1999.

Inthisnewedition,Ihavereviewedandincorporatedtheknowledgeacquiredrecentlybymany laboratoriesthathavepublishedonthesubjectofaluminiumcorrosionanditsmetallurgicalaspects. In20years,newinvestigativemethodshavealsomadeitpossibletoexplainmanyofthephenomena involvedinstructuralcorrosion.

Asaresult,thisneweditionof CorrosionofAluminium,whilemaintainingitspracticalorientation tomeettheneedsofaluminiumusers,givesalargeplacetotheresultsofthehigh-qualityscientiﬁc publicationsofthemanyresearchersdedicatedtothestudyofaluminiumcorrosion.1

Likethepreviousversion,thisneweditionaimsatawidereadershiprangingfromaluminium userstoacademia.Bothwillﬁndusefulinformationonaluminiumcorrosionbasedonthestateof knowledgeacquireduptothetimeofwritingthisnewedition.

Iwouldliketothankallthosewhohavegivenmetheirprecioussupportinthewritingofthisbook:

➢ DrLionelPeguet,corrosionandsurfaceR&Dengineer,CTECConstelliumTechnologyCentre, Voreppe,France

➢ Jean-SylvestreSafrany,researchengineer,SurfaceTreatments,CTECConstelliumTechnology Centre,Voreppe,France

➢ Franc¸oiseSaillard,informationspecialist,CTECConstelliumTechnologyCentre,Voreppe,France

➢ DamienFe ´ ron,CEASaclay,France,presidentoftheEuropeanCorrosionFederation

➢ BrunoSavelli,CEASaclay,France,DirectiondelaRechercheFondamentale,Servicede Valorisationdel’Information

1Over2000publicationsonaluminiumcorrosionpublishedfromthebeginningofthe20thcenturyuptothepresentdayhave beencitedinthisbook.

➢ PhilippeMarcus,directorofresearchattheCentreNationaldeRecherchesScientiﬁque(CNRS), ChimieParisTech

➢ MichelJannier,expertinaluminiumsurfacetreatmentprocesses

➢ MichelPinc¸on,expertinaluminiumsurfacetreatmentprocesses

➢ MichelGarat,aluminiumfoundryconsultant,formerPechineyR&Dmanager

➢ HassinaFounas,executiveassistantoftheFrenchAnti-CorrosionCentre(CEFRACOR),Paris

IwouldliketothankHughDunlopforagreeingtotranslatemytextintoEnglish.IchoseHugh becauseofhisexperienceandknowledgeofaluminiumsurfacephenomenaandsurfacetreatments, havingbeenanengineerandgroupleaderintheConstelliumCTECVoreppeResearchCentre (formerlyPechiney & Alcan)for27yearsandhimselftheauthorofmanypublications.

IwouldalsoliketoexpressmythankstoGeoffScamans,chiefscientiﬁcofﬁceratInnoval Technology(Banbury,UK)forhisexpertreviewofseveralchapters,particularlythoserelatingto thedifferenttypesofaluminiumcorrosion.Iamverygratefulforhisknowledgeableinput.

IwouldliketoexpressmygratitudeonceagaintoAndre ´ Guilhaudis(1918 2008),whowas Pechiney’scorrosionexpertfrom1945to1980.HewelcomedmetothePechineyResearchCentre inChambe ´ ryin1957andsharedwithmehispassionforaluminiumandhisexperienceincorrosion.

C.VARGEL

Inge ´ nieurENSEEG 15November2019

Introductoryremarks

Itiscustomary,andforconvenience,torefertoaluminium,butwhatismeantinmostcasesare aluminiumalloys.Itshouldberecalledthatunalloyedaluminiumaccountsforjustover10%ofthe world’sannualconsumptionofallaluminiumproducts.

However,forthesakeofsimplicity,Iuse‘aluminium’insteadofthetraditionalexpressions ‘aluminiumanditsalloys’or‘aluminiumandal uminiumalloys’.Itshouldnotbeconcludedthat thecorrosionresistanceofallaluminiumalloys isthesameinanyenvironment!Therearecertainly somesimilarities,buttherearealsoimportantdifferencesbetween2XXXand7XXXseriesalloys andthoseoftheotherfamilies.ThatiswhyIhavemadethisdistinctionwheneverappropriate.

Whenoneormorealloyshavebeenusedforcorrosiontestsinagivenenvironment,itseemed desirabletometomentionthembecausetheywerepartofthetestprotocolchosenbythescientists andcontributedtoitsvalidation.Similarly,itseemsessentialtoindicatethealloyscommonlyused inanapplication.Thesearereferencesthathelptoestablishtheuseandstrengthenthechoiceof prescribersandusers.

ThedesignationofwroughtandcastalloysemployedisthatoftheAluminumAssociation1 [1].To facilitatethereadingofPartsEandFdealingwiththecorrosionresistanceofaluminiuminchemicals, Ihavequoted(between{})theirADRnumber,2 whichistheUnitedNationsfour-digitcodeforthe substanceinquestion.ThedesignationoforganicchemicalslistedinPartsMandNshallpreferablybe thataccordingtotherulesofIUAPCnomenclature.3

Excludedfromthescopeofthisworkarealuminiumpowderproducts,powderandgranuleswhose propertiesandapplicationsarenotrelatedtotheapplicationsofcastproducts,wroughtsemiﬁnished products,rolledproducts,extrudedproductsandsoon.Alsoexcludedaresinteredaluminiumpowder compositesaswellasaluminizedsteel.

Reference

[1]KaufmanJB.Understandingwroughtandcastaluminiumalloysdesignations.[Chapter3],ASM International,p.23 37. https://doi.org/10.1361/iaat2000p023.

1TheAluminumAssociation,1400CrystalDriveSuite,430ArlingtonVA22202. 2ADR,accordfordangerousgoodsbyroad.

3IUAPC,InternationalUnionofPureandAppliedChemistry.

Historicalreviews A.1

Chapteroutline

1.1Chemicallyproducedaluminium........................................................................................................4

1.2Electrochemicallyproducedaluminium..............................................................................................4 References..............................................................................................................................................6

ThechemistLouisGuytondeMorveau(1736 1816),aco-workerofAntoineLaurentLavoisier (1743 1794),coinedtheword‘alumine’foroneofthesulphatescontainedinalum. Alumine is derivedfromtheLatinword alumen,whichissaidtohavebeenusedforpotassiumalum KAl(SO4)2 12H2OduringtheRomanperiod.Aluminiumcompoundswereusedinlargequantitiesin antiquepottery,asdyestuffandasanastringentinmedicine [1].Itisnottheword‘alumine’thathas cometodesignatealuminiumorebuttheword‘bauxite’.Thisisbecausein1821PierreBerthier (1782 1867),aminingengineer,discoveredthattheredsoilofthevillageLes-Baux-de-Provencein Francecontained40 50wt.%ofwhathetermed‘hydratedalumina’ [2].

Subsequently,in1861FrenchchemistHenriSainte-ClaireDevillenamedtheore‘bauxite’.In fact,bauxitecompositionsvarydependingonthesourceoforebuttheyusuallycontainaluminium hydroxidessuchasgibbsiteAl(OH)3,boehmite g-AlO(OH)anddiaspore a-AlO(OH),therestbeing composedessentiallyofironoxidesandhydroxides,mainlyhaematite, a-Fe2O3 andgoethite FeO(OH)(thesourceofitsredcolour),andthealuminosilicateclaymineralkaolinite,Al2Si2O5(OH)4. EventhoughitisthemostabundantmetalintheEarth’scrust(83,000ppm)andthethirdmost abundantelementafteroxygenandsilicon,aluminiumdidnotbecomeanindustrialmetalbeforethe endofthe19thcentury.Aluminaisoneofthemoststableofalloxides,withanenthalpyofformation, DG,of 1,582kJ$mol 1 (theenthalpyofironoxideis 1,015kJ$mol 1).Itishenceverydifﬁcultto reducealumina.

ThediscoveryofmetallicaluminiumisattributedtoSirHumphreyDavy(1778 1829).He referredtoitusingtheterm‘aluminium’in1809.Byelectrolysisofmoltenaluminiumsalts,he obtainedanalloyofaluminiumwithiron,becausehehadusedanironcathode [3].ThechemistHans ChristianOersted(1777 1851)andlaterFriedrichWo ¨ hler(1800 1882)chosetoreducealuminium chloridewithpotassium.Thechloridehadbeenpreparedbychlorinationofbauxiteinthepresenceof carbon.ItwasWo ¨ hlerwho,in1827,succeededinproducingasufﬁcientlypuremetaltodetermine someofitsproperties,mostnotablyitslowdensity.

CorrosionofAluminium. https://doi.org/10.1016/B978-0-08-099925-8.00001-6

Therewereinitiallytworoutesfortheindustrialproductionofaluminium:

•Byachemicalmethod(1856 1889);

•Followedbytheelectrochemicalprocessinventedin1886andstillinusetoday.

1.1Chemicallyproducedaluminium

In1854,HenriSainte-ClaireDeville(1817 1881)improvedWo ¨ hler’sprocess.Hereplacedpotassium withsodiumfortworeasons:thereductionof1molofAluses3molofsodium,totalling60g,instead of3molofpotassiumamountingto117g.Atthattime,sodiumwaslessexpensivethanpotassium.He alsoreplacedaluminiumchloride,whichisrathervolatile,withasodiumaluminiumchloride.

TheﬁrstplantwascreatedinParis,in1856,inthe‘LaGlacie ` re’area,butsoonitwasshutdown:

‘ThesmallplantofLaGlacie`re,locatedinaninnersuburbofParis,amidsthousesandmarket gardens,releasingintotheatmospheresmokeladenwithsodaandchlorine,wasforcedtoceaseits aluminiumproductionafternumerouscomplaints’ [4].

Inthespringof1857,Sainte-ClaireDevillemovedtheplanttoNanterre(nearParis),farawayfrom residentialareas.In1859,productionreached500kg.Thatsameyear,whenLouisLeChatelierhad patentedareductionprocessofaluminawithsodiumcarbonate,aplantwasbuiltinSalindres,closeto Ale ` sintheGardFrenchdepartment,notfarfromthebauxitesupplyandthesaltﬁeldsofLaCamargue. TheproductioninSalindreshadvariedfrom505kg,whentheplantwasstartedin1860,to2,959kgin 1880,whenthisprocesswasdiscontinued.

Theﬁrstkilogramsofaluminium,producedin1856,weresoldslightlymoreexpensivethansilver, around300francs,equivalenttoUS$3,200in2016.Duringthedecade1880 1889,themetal producedinSalindreswassoldforbetween60and70francsperkilo,theequivalentofUS$750 800 in2016.Aluminium,whichSainte-ClaireDevillelikedtocomparetosilver,wasmainlyusedfor silverwareandjewellery.CharlesCristoﬂe(1805 1863),thecelebratedParisiansilversmith,produced castartworkmadeofaluminiumalloyedwith2%wt.copper.In1858,thesonofNapoleonIIIwas offeredarattlemadeofaluminium.

1.2Electrochemicallyproducedaluminium

In1871,Ze ´ nobeGramme(1826 1901)inventedthefirstrevolvingmachinecalleda‘dynamo’.The useofpowerfulsourcesofdirectcurrentmadeitpossibletoenvisionproductionmethodsbasedon electrolysis.Sainte-ClaireDevillehadtriedunsuccessfullytoelectrolysemoltenaluminiumchloride. ThemanufacturingprocessofaluminiumbyelectrolysisofmoltenaluminawasdevelopedinFrance byPaulLouisToussaintHe ´ roult(1863 1914),whofiledapatenton23April1886,andintheUnited StatesbyCharlesMartinHall(1863 1914),whofiledhispatenton9July1886.Bothhadsucceeded indissolvingalumina(meltingpoint2030 C)incryolite3NaF AlF3,whichmeltsat977 C,withthe industrialmeltcontainingabout2 3wt.%alumina.

In1887,Bayerﬁledapatentforamethodtoextractaluminafrombauxitebasedontheattackof bauxitebyhotcausticsoda.He ´ roultwenttoNeuhausen,Switzerla nd,inordertosetuphisprocess. Theyearafter,hereturnedtoFranceandin1888createdtheFrogesplantnearGrenobleinFrance wheretheproductionwas1,100kgin1889.SeveralplantsweresetupinFrance,Switzerland, andtheUnitedStates.Sixthousandmetrictonswereproducedin1900,andthesalespriceof

TableA.1.1Worldproductionofprimaryaluminium

19006 191044 1920125 1930270 1940780 19501,500230 19604,450790 197010,5002,230 198015,4004,670 199019,5008,470 200024,65012,700 201042,30020,200 201557,70025,000 201659,900 201763,400

FrompublishedrecordsoftheWorldAluminium InternationalAluminiumInstitute.

aluminiumstabilizedataroundUS$3.30perkilogr am.Thiswasthestartoftheindustrialadventure ofaluminium.Theworldproductionofso-calle dprimaryaluminiumamountedto6,000tonnes in1900(see TableA.1.1 )andhassteadilyincreased(see Fig.A.1.1),especiallysince1950.More recentlytherehasbeenafurthersharpincreaseassociatedwiththedevelopmentofChinese production(<5,000kTin2000to >30,000kTby2015).

FIGUREA.1.1 Worldproductionofprimaryaluminium.

Itisworthnotingthat,duetoitsinherentresistancetocorrosionandmorerecentlythroughthe developmentofaluminiumrecycling,75%oftotalworldaluminiumproduction(w750MT)isstillin productiveuse(eversince1888).

References

[1]Dictionnairehistoriquedelalanguefranc¸aisesousladirectiond’AlainRey.Paris:EditionsRobert;1994. p.55.

[2]BerthierP.Analysedel’aluminehydrate ´ edesBauxdeProvence.AnnalesdesMines1829;5(2):531 4.

[3]PascalP.Nouveautraite ´ deChimiemine ´ rale.e ´ diteurs,Paris:MassonetCie;1960.

[4]Saint-ClairDevilleH.Del’aluminium.Sesproprie ´ te ´ s,safabrication,etsesapplications.Paris:MalletBachelier,Imprimeur-Libraire;1859.p.8.

CHAPTER

Physicalpropertiesof aluminium A.2

Theprincipalphysicalpropertiesofunalloyedaluminiumarelistedin TableA.2.1

TableA.2.1Propertiesofunalloyedaluminium

Longitudinalelasticmodulus,EMPa69,000

Poisson’sratio, n 0.33

aThisisthegenerallyacceptedvalueforthedensityofmetalbetween99.65%and99.99%pure.At700 C,thedensityof moltenmetalof99.996%purityis2,357kg.m 3 CorrosionofAluminium. https://doi.org/10.1016/B978-0-08-099925-8.00002-8

Thereflectivityofbareandanodizedaluminiumdependsbothonthesurfaceaspectandonthe wavelength(Fig.A.2.1).Reflectivityincreaseswithpurity:withbrightmetalanodizedtoanoxide thicknessof5 mm,reflectivityincreasesfrom75%onmetalwithapurityof99.6%to85%reflectivity fora99.99%puremetal(Fig.A.2.2).

FIGUREA.2.1

Reﬂectivityofaluminium,silver,goldandcopper.

FIGUREA.2.2

Effectofpurityonthereﬂectivityofanodizedaluminium(5 mmthickanodizationlayer).

Theadvantagesofaluminium A.3

Chapteroutline

3.1Thehymnofthecannonball

PresidentBarbicanhad,withoutlossoftime,nominatedaworkingcommitteeoftheGunClub.The dutyofthiscommitteewastoresolvethethreegrandquestionsofthecannon,theprojectile,andthe powder.

Gentlemen,saidhe,wehavetoresolveoneofthemostimportantproblemsinthewholeofthenoble scienceofgunnery.Itmightappear,perhaps,themostlogicalcoursetodevoteourﬁrstmeetingtothe discussionoftheenginetobeemployed.

Theproblembeforeus,continuedthepresident,ishowtocommunicatetoaprojectileavelocityof 12,000yardspersecond.

Thesideswillrequireathicknessoflessthantwoinches. Willthatbeenough?askedthemajordoubtfully. Clearlynot!repliedthepresident.

Whatistobedone,then?saidElphinstone,withapuzzledair. Employanothermetalinsteadofiron. Copper?saidMorgan.

No!thatwouldbetooheavy.Ihavebetterthanthattooffer. Whatthen?askedthemajor.

Aluminium!repliedBarbican. Aluminium?criedhisthreecolleaguesinchorus.

Unquestionably,myfriends.Thisvaluablemetalpossessesthewhitenessofsilver,theindestructibilityofgold,thetenacityofiron,thefusibilityofcopper,thelightnessofglass.Itiseasilywrought, isverywidelydistributed,formingthebaseofmostoftherocks,isthreetimeslighterthaniron,and seemstohavebeencreatedfortheexpresspurposeoffurnishinguswiththematerialforour projectile.

Whatwilltheprojectileweighthen?askedMorgan.

Hereistheresultofmycalculations,repliedBarbican.Ashotof108inchesindiameter,andtwelve inchesinthickness,wouldweigh,incast-iron,67,440pounds;castinaluminium,itsweightwillbe reducedto19,250pounds.

Capital!criedthemajor;butdoyouknowthat,atninedollarsapound,thisprojectilewillcost

Adopted!repliedthethreemembersofthecommittee.Soendedtheﬁrstmeeting.Thequestionofthe projectilewasdeﬁnitelysettled.

From TheEarthtotheMoon,Chapter7 JulesVerne,1865.

Withanannualworldconsumptionof59milliontonsin2016,aluminiumistheleaderinthe metallurgyofnon-ferrousmetals.Theproductionofaluminiumhasbeenincreasingsteadilysince 1950(see Fig.A.3.1).

Shareofprimaryandrecycledaluminiumintotalaluminiumproduction.

FromWorldAluminium InternationalAluminiumInstitute.

FIGUREA.3.1

Thedevelopmentofapplicationsforaluminiumanditsalloys,aswellasthesustainedrisein consumption,canbeattributedtoseveralofitspropertieswhicharedecisivecriteriainusers’choiceof metals,especiallyintheﬁeldsoftransport,building,electricalengineeringandpackaging. Theseadvantageouspropertiesare:

➢ Lightness;

➢ Thermalconductivity;

➢ Electricalconductivity;

➢ Suitabilityforsurfacetreatments;

➢ Corrosionresistance;

➢ Diversityofaluminiumalloys;

➢ Diversityofsemi-products;

➢ Functionaladvantagesofextrudedandcastsemi-products;

➢ Easewithwhichaluminiumcanbeformed;and

➢ Easeofrecycling.

3.2Lightness

Thediscoverersofaluminiumwereparticularlyimpressedbythelowdensityofthismetal.

‘Aluminiumismuchlighterthananyothercommonmetal,andthekindofsensationwhichitgivesyouto carryaningotofthismetalisalwaysamazing,evenifyoualreadyknowaboutthispeculiaraspect’ [1]

Lightnessisthepropertyofaluminiumthatﬁrstspringstomind,somuchsothatforalongtimethe term‘lightalloy’wasusedforwhatisnowcalled‘aluminiumalloys’.Aluminiumisthelightestofall commonmetals(TableA.3.1).Itsdensityis2,700kg.m 3,whichisalmostthreetimeslessthanthatof steel.Thedensityofaluminiumalloysrangesfrom2,600to2,800kg.m 3

Experiencehasshownthatanaluminiumalloystructurecanbeupto50%lighterthanits equivalentmadefrommildsteelorstainlesssteel.Thistakesintoaccountthemodulusofelasticity (one-thirdofthemodulusforsteel)andthefatiguelimitsofweldedorboltedstructuresmadeof aluminiumalloys.Itisnotappropriatetosimplytransposetherulesforsteeldesigntoaluminium. Rather,thespeciﬁcpropertiesofaluminiumneedtobetakenintoaccount.

Severalareasoftechnologytakeadvantageofaluminium’slightness:

➢ Transportbyland,seaorair.Theneedtolimitemissionsofcarbondioxideandotherpollutinggaseous emissionsmeansthatthefuelconsumptionofcarsmustbereduced.Theyneedtobelightened. Aluminiumisthematerialchosenmoreandmorefrequentlytomeetthischallengefacingthe automotiveworld.Inordertoachieveweightsavingsinhigh-speedferries,shipyardshaveturned toaluminiumalloysofthe5XXXand6XXXseries.Experiencehasshownthatweightsavingsin hullstructurescanalsobeashighas40 50%comparedtoanequivalenthullstructuremadeofsteel;

➢ Ontheotherhand,aluminiumhasalwaysbeenthemainmaterialusedforthefabricationofaircraft load-bearingstructures(wings,fuselageandempennage)andforspaceapplications.Althoughnow undercompetitionfromcarbonﬁbrereinforcedplasticcomposites(CFRP)forcertainaircraft applicationssuchaswingsincivilairliners,itisstillmaintainingitsleadershipduetothe developmentofnewhigh-performancealloyssuchasAlCuLialloyslikeAA2198,AA2050, AA2090andothers.ItalsoholdsseveralundeniableadvantagesoverCFRP,includingthoseof damagetoleranceandisotropicmechanicalproperties,recyclability,electricalandthermal conductivityandcost;

TableA.3.1Comparisonoftypicalproperties

Meltingpointor meltingrange( C)

Volumicmass, r (kg.m 3)2,7002,7902,6602,8107,8207,9008,940

Coefﬁcientoflinearexpansion, a1, at20 100 C(10 6 K 1)

Thermalconductivity, l at 20 C(W.m 1.K 1)

Electricconductivityat 20 C(mS.m 1)

Proofstress, Rp0.2 (MPa)80275215505240 >23069

Tensilestress, Rm (MPa)115425305570410 700235

Elongation, A (%)621101024 5045

Elasticmodulus(MPa)69,00072,50071,00072,000210,000200,000115,000

Brinellhardness(HB)351109016011020045

Meanvalues,givenforguidance.

➢ Mechanicalengineering.Thereplacementofasteelcomponentbyoneofthesamesizemadefrom a2XXX,7XXX,5XXXor6XXXseriesalloyleadstoaweightsavingontheorderofthedensity ratio,thatis,60%.Aluminiumiswidelyusedformovingparts,forexampleinrobots,inorderto minimizeinertia.

Lightnessisnotonlyanadvantagefortheapplicationitself,butalsoaffectsfactoryoperationsand workingconditions.Handlingsemi-productsandcomponentsmadeofaluminiumalloysiseasier, potentiallycuttingthecapitalcostofhandlingequipment.

3.3Thermalconductivity

Unalloyedaluminiumisanexcellentheatconductor,withroughly60%ofthethermalconductivityof copper,theoptimumperformeramongcommonmetals.Thethermalconductivityofaluminiumalloys dependsontheircompositionandmetallurgicaltemper.Asearlyastheendofthe19thcentury,this propertyledtoreplacingtin-platedcopperwithaluminiumalloysinthemanufactureofkitchen utensils,bothfordomesticandprofessionaluse.

Wheneverthereisaproblemrelatedtoheatexchange,theuseofaluminiumisalwaystakeninto consideration,underthecondition,ofcourse,thatthemediumisappropriatewhenliquid liquidor liquid gaseousexchangeisenvisaged.Therearemanyapplicationsofaluminiumheat-exchangers: cars,commercialvehicles,refrigerators,airconditioning,desalinationofseawater,solarenergy, coolersinelectronicdevices,andsoon.

3.4Electricalconductivity

Theelectricalconductivityofaluminiumisaroundtwo-thirdsthatofcopper,whichitisreplacingfor manyelectricalapplications.OverheadpowertransmissionlinesmadeofaluminiumorAlmelec-type aluminium,onthemarketinFrancesince1927 [2],areusedthroughouttheworld.Aluminiumbars andtubesarealsowidelyusedinconnectingstationsforhigh-andmedium-voltageoutdoornetworks.

3.5Resistancetocorrosion

Sainte-ClaireDevilleobservedthataluminiumhadgoodresistancetoatmosphericcorrosion,which includedtheparticularatmosphereofgaslamps(usedforstreetlightingduringthe19thcentury), whichwasladenwithhydrogensulphide(H2S).Healsorecognizedtheverygoodresistanceof aluminiumincontactwithwater.

Manydecadesofexperiencewithitsuseinbuildings,publicworks,shipbuilding,andsoonhave conﬁrmedtheobservationsofthe19thcenturychemists.Aluminiumandthealloysofthe1XXX, 3XXX,5XXX,6XXXand8XXXserieshaveexcellentresistancetoatmosphericcorrosioninthe marine,urbanandindustrialenvironments(seeChapterH.5).

Thisverygoodresistancetocorrosion,asmuchaslightness,explainsthedevelopmentof numerousaluminiumapplicationsandoffersusersanumberofmajoradvantages:

➢ Equipmentandcomponentscanhaveaverylongservicelife,extendingtoseveraldecades; 1

➢ Maintenanceisminimal,evenwhennoextraprotection(painting,anodizing)isprovided;

➢ Appearanceispreservedlonger,becauseofaverygoodresistancetocorrosion.2

3.6Suitabilityforsurfacetreatments

Aluminiumsurfacetreatmentscanserveseveralpurposes,including:

➢ Protectingcertainalloysiftheirnaturalcorrosionresistanceisdeemedinsufﬁcient,oftenthecase withcopper-containingalloysofthe2XXXand7XXXseries;

➢ Preservingthesurfaceaspect,inordertoavoidpittingcorrosionorblackening;

➢ Modifyingcertainsurfacepropertiessuchassuperﬁcialhardness;

➢ Decoratingthemetal.

3.7Thediversityofaluminiumalloys

Witheightseriesorfamilies,aluminiumalloysareverynumerousandofferawiderangeofcompositions,propertiesanduses.

Thecontinuingprogressinthemetallurgyofaluminiumhasproducedhigh-performancealloys thatarewellsuitedtoalltypesofapplications,usingconventionalorspecialfabricationtechniques amongothers.Whilealloysinthesameseriessharecommonproperties,oneseriescandiffergreatly fromanother,andcertainpropertiescanvarywidely.Thusalloysinthe5XXXseriesareweldableand generallyhavegoodcorrosionresistance,whilealloysinthe2XXXserieshavebettermechanical properties,butcannotbeweldedusingconventionaltechniques,andtheirresistancetoatmospheric corrosionispoor.

Howevertemptingtheprospect,thismeansthatitisnotalwayspossibletoswitchfromoneseries toanotherinthesearchforbettermechanicalproperties.Forexample,onewouldnotreplaceAA6061T6byAA2017A-T4withoutathoroughanalysisoftheprevailingserviceconditions.Otherwise,a choicebasedonasinglecriterion,heremechanicalproperties,maywellpenalizetheuseronother propertiesincludingcorrosionresistance.

3.8Thediversityofsemi-products

Thetransformationtechniquesofaluminiumrolling,extrusionandcastingpresentdesignersand manufacturerswithaverywiderangeofsemi-products:

➢ Castings:sandcastingsforsmallseries,mouldcastingsforlargeseries;

➢ Flatrolledproducts:plateandsheet,treadplate,coil-coatedsheet,andothers;

1Itisnotuncommontoﬁndinserviceasrooﬁng[includingthatofachurchinRome(seeChapterH.5, x1)],claddings, marinaequipmentandboatsthathavehadseveraldecadesofservice.

2Aluminiumcorrosionproductsarewhite.Theydonotstainbareorpaintedmetalsurfaceslikerustdoesonsteel.

➢ Extrusions:holloworfullproﬁles,instandardorcustomizedshapes;

➢ Die-forgedorhand-forgedproducts.

Severalalloysarecompatibleforweldingpurposes.Rolledorextrudedsemi-productsofthe 3XXX,5XXXand6XXXXseriescanbejoinedwithcastingsinalloys356.0,357.0and360.0by meansofTIGandMIGwelding.

Thisdiversityofsemi-productsmakesitpossibleto:

➢ Selecttherightlocationforstressesoncomponentsofboltedorweldedstructures;

➢ Simplifyﬁnishingprocessesbyusingcoil-coatedorpre-anodizedsheets;

➢ Saveonthetimeneededforassembly,whichcancompensatefortheaddedrawmaterialcostof structuresmadefromaluminiumalloyscomparedwithequivalentsteelstructures.

3.9Thefunctionalityofcastingsandextrusionsfunctionality

Castingmakesitpossibletomanufacturepieceswithcomplexshapesandseveralfunctions,reducing complexmachiningtosimplemachiningorsurfacemilling.Extrusionallowsmanufacturingproﬁles withaverywiderangeofdimensionsandshapes,proﬁlesthatarewellsuitedtotheneedsofdesigners whoneedtoselecttherightlocationforstressesonstructures.Extrusiondiesarenormallyeasyto manufactureatamoderatecost.3

3.10Easeofuse

Providedthatcertainrulesspeciﬁctoaluminiumalloysareobserved,aluminiumalloyscanbeprocessedusingthesameconventionaltechniquesofshaping,bending,fabrication,deepdrawingand machiningasusedforothercommonmetalssuchasmildorstainlesssteel.

Aluminiumalloyscanusuallybeprocessedwithouttheneedforspeciﬁcequipmentormachine tools.Itisadvisable,however,tosetupaworkshopdedicatedtoaluminiumalloyprocessing;this workshopshouldbeseparatedfromtheworkshopprocessingsteelandespeciallycopperalloys.Like allothercommonmetals,aluminiumalloyslendthemselvestojoiningtechniquessuchaswelding, brazing,riveting,bondingandsoon.

3.11Recycling

Aluminiumrecyclingisundercontinualdevelopment,bothinthecontextofenergysavingsandfor economicreasons.Aluminiumre-meltingrequiresonly5%oftheenergythatisneededtoextractthe primarymetalfromitsore.Decadesofexperiencewithscrapcollectinghaveshownthataluminium scrapalwayshasahighermarketvaluethansteelscrap.Alsosigniﬁcantisthesteadyriseinthe consumptionofrecycledmetaloverthelast20years;itnowstandsatabout30%oftheproductionof primaryaluminium(Fig.A.3.1,p.10).

3Itispossibletomaketools(dies)forareasonablecosttomakecustomizedproﬁlesadaptedtoaspeciﬁcuse.

References

[1]Saint-ClairDevilleH.Del’aluminium.Sesproprie ´ te ´ s,safabrication,etsesapplications.Paris:MalletBachelier,Imprimeur-Libraire;1859.p.15.

[2]SuhrJ.Unalliaged’aluminium-magne ´ sium-silicium,l’Almelec.Revuedel’AluminiumAvril1927;(18): 412 22.

Aluminiumalloyseries A.4

Chapteroutline

4.1Alloyseries....................................................................................................................................18

4.2Alloyingelements...........................................................................................................................19

4.3Additives.......................................................................................................................................19

4.4Impurities......................................................................................................................................19

4.5Designationofaluminiumalloys................................................................................................

Unalloyedmetalsgenerallyhaveonlyfewapplications:whiletheyexhibitver yparticularproperties, thesepropertiesareoftenlimitedtoaverynarrowﬁeldofapplication.Theartofthemetallurgististo createalloysfromagivenbasemetal,beitcopper,ironoraluminium,byaddingcontrolledamounts ofothermetals(ormetalloids)inordertoimprove ormodifycertainpropertiessuchasmechanical properties,formabilityorweldability.Thisishow,morethan5000yearsago,themostancient metallurgistsdiscoveredthatbyaddin gtintocopper,theyproducedanalloy bronze thatwas easytomouldandthatofferedanoutstandingresistancetomarinecorrosion.

Sainte-ClaireDevillepreparedanaluminiumalloycontaining10wt.%silicon.Thesilversmith CharlesCristoﬂe 1 usedanalloycontaining2wt.%copper,thusharderandeasiertochisel,for objectshemanufacturedinaluminiumdu ringtheSecondEmpireinFrance(1852 1870). Immediatelyafterthedevelopmentof electrolysisofmoltensaltsbyPaulHe ´ roultinFranceand CharlesMartinHallintheUnitedS tatesin1866,metallurgiststrie dtoimprovethepropertiesof aluminiumsuchasmechanicalresis tance,resistanceathightemper atures,machinability,corrosion resistanceandsoon.

Researchanddevelopmentworkcarriedoutforover100 yearsonthecompositionofalloys, theirtransformationprocesses,theheattreatmen tprocessesandonoptimiz ingallthesefactorshas resultedinawiderangeofalloys,fromwhichuser scanselectthosebestsuitedtotheirspeciﬁc requirements.

1CharlesChristoﬂe(1805 1863)wasaParisiansilversmithandfounderofthecompanyofthesamename.Hemadesome famousaluminiumcutlery.

Amplitudeofthemechanicalpropertiesofaluminiumalloys(minimumvaluesonsheets1.5 3mmthick, accordingtostandardEN485-2).

Thediversityofalloysandthewiderangeofcertainpropertiessuchastheirtensilestrengthranging from100to700MPaexplainsthegrowthinapplications,bothnumerousandvaried,fromaeronautics topackaging(Fig.A.4.1).

4.1Alloyseries

Allaluminiumproductsbelongtooneofeightalloyseries.Theyareavailableascastingsandwrought semi-productsthatareﬂatrolled,extrudedorforged.

Alloysbelongingtothesameseriesexhibitasetofcommonpropertiessuchascastability, mechanicalproperties,extrudability,corrosionresistanceandothers.Thesepropertiescanvary considerablyfromoneseriestoanother.Foragivenuse,itisthereforenotalwayspossibleor desirabletoswitchtoanotherseries.

Thesameappliestometallurgicaltempers.Astr ain-hardenedtemper(temperH1X)willnothave thesamedeformationcapacityasasofttemper(te mperO)instrain-hardenablealloys,andasan agedtemper(temperT4)inage-hardenablealloys.Thechemicalcompositionofindustrialalloysis inﬂuencedbyalloyingelements,additivesandimpurities.

FIGUREA.4.1