w w w . j m r t . c o m . b r
Availableonlineatwww.sciencedirect.com
Original Article
Technical and environmental evaluation of a new high performance material based on magnesium alloy reinforced with submicrometre-sized TiC particles to develop automotive lightweight components and make transport sector more sustainable
Victor Ferreira
a, Mikel Merchán
b, Pedro Egizabal
b, Maider García de Cortázar
b, Ane Irazustabarrena
b, Ana M. López-Sabirón
a, German Ferreira
a,∗aResearchCentreforEnergyResourcesandConsumption(CIRCE),CIRCEBuilding–CampusRíoEbro,MarianoEsquillorGómez,15, 50018Zaragoza,Spain
bFundaciónTecnaliaResearch&Innovation,DepartamentodeFundiciónySiderurgia,MikeletegiPasealekua2,20009Donostia-San Sebastian,Spain
a r t i c l e i n f o
Articlehistory:
Received28December2018 Accepted27February2019 Availableonline29May2019
Keywords:
Magnesium Submicrometre Titanium-carbide Life-cycle-assessment CO2eqemissions
a bs t r a c t
Thisstudyevaluatedtheuseofsubmicrometre-sizedparticlesbasedontitaniumcarbide frombothtechnicalandenvironmentalpointsofview.Theobjectivewastoimprovethe mechanicalpropertiesofthemagnesiumalloyintendedforuseintheautomotivecom- ponentindustry.Tothisend,anAl/TiCmastercompoundcontaining60wt.%ofTiCwas producedthroughaself-propagating,high-temperaturesynthesisprocessandembeddedin amagnesiumalloybyamechanicalstirringmethod.Thelifecycleassessmentmethodology wasthenusedtoevaluatetheenvironmentalimpactofthemanufacturingofthemagne- siumalloyreinforcedwithsubmicrometre-sizedparticles.X-raydiffractionandscanning electronmicroscopytechniquesrevealedthenatureandpurityoftheTiCpresentinthe materialandrevealedparticlesizesbelowsubmicrometrerange(300–500nm).Theincorpo- rationofTiCparticlesintothemagnesiumalloyresultedinimprovementsinyieldstressand ultimatetensilestrengthofmorethan10%and18%,respectively,andincreasesinductility valuesby30%.Finally,theresultsindicatedthatthesubmicrometreparticleproductionhad alowenvironmentalimpactcomparedwiththetotalimpactassociatedwithmanufacturing
Abbreviations: CMA,Chinesemagnesiumassociation;CTE,coefficientofthermalexpansion;EC,Europeancommission;EU,Euro- peanunion; GHG,greenhousegas; LCA,lifecycleassessment; LCI,life cycleinventory;SEM,scanningelectron microscopy;SHS, self-propagatinghigh-temperaturesynthesis;XRD,x-raydiffraction.
∗Correspondingauthor.
E-mail:[email protected](G.Ferreira).
https://doi.org/10.1016/j.jmrt.2019.02.012
2238-7854/© 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
themagnesiumalloyreinforcedwithsubmicrometre-sizedparticles;thegreatestenviron- mentalburdenwasattributedtothemagnesiumproductionstage.However,thisimpactis offsetintheusephaseofthevehicle,providingapproximately28,000kmofmileagefora car.
©2019TheAuthors.PublishedbyElsevierB.V.Thisisanopenaccessarticleunderthe CCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).
1. Introduction
Thetransportsectorisoneofthemostpollutingsectorsin Europe.AccordingtotheEuropeanCommission[1],thissector releasesmorethan50%ofthetotalNOxemissions,approxi- mately60%ofCOemissions,and25%oftotalenergy-related CO2emissions.Consideringthelattervalue,80%ofCO2emis- sionscomespecificallyfromroad transport.Passengercars providethe largestcontribution, approximately45% ofCO2
emissions.Accountingforthis,oneofthemainprioritiesof theEuropeanpoliciesistoreduceGreenhouseGas(GHG)emis- sions by60% compared tothe 1990 levels [2]. Thecurrent Europeanstrategyrecognisesthepositive resultsofcertain measuresalreadytakenattheEuropeanUnion(EU)level,but hasunderlinedthatfurtherprogressisrequiredinresearch andtechnologicaldevelopment,inparticulartoreduceCO2 emissions[3].
Several strategies have since been launched. Some improvementsarebeingachievedintheperformanceofcon- ventionalengines,forexample,usingvariablegeometriesof thevalveliftandthethroatdiameter[4],introducingselec- tivecatalyststoreduceemissions[5],oradaptingtheengine forusingalternativefuelsorblends[6,7].Additionally,alter- nativetechnologiestotheconventionalengineswithalower emissionratioarebeingdeveloped,suchaselectricvehicles, whichmaybeself-containedwithageneratortoconvertfuel toelectricity(hydrogenfuelcells)[8,9]orabatterythatmay bepoweredthroughacollectorsystembyelectricityfromoff- vehiclesources[10,11].
Finally, a current strategy is to improve car design by using lightweight materials to produce the car body and its components, decreasing the total weight and thus, the fuel consumption and associated emissions [12,13].
The most used materials in the automotive sector are steel and aluminium [14]. However, in recent years, there have been attempts in the automotive sector to substi- tute these materials with lighter ones, such as composite materials based on glass fibres [15], polymers [16], and magnesium [17]. The latter is the most promising mate- rialforstructuralcomponentsasitisthelighteststructural metal.
Thedensityofmagnesiumisaround33%lowerthanthat ofaluminiumandapproximatelyafifththatofsteel.There- fore, there is an opportunity to save fuelby using this in vehiclecomponentsand,consequently,achievetherequired CO2emissionreduction.Nevertheless,itisalsoimportantto evaluatethemechanicalpropertiesresultingfromtheutilisa- tionofmagnesiumalloysincarpartsandtoensurethatthey canaccomplishthetechnicalrequirementsoftheautomotive sector.
AsreportedbyGuptaandWong[18],althoughmagnesium alloycomponentscanbeobtainedfromcastprocesses,these canexhibitdisadvantageswithregardstoelasticity,ductility, and resistance properties. Although some surface protec- tionmaterialssuchasfibrousszaibelyite[19]orotherstable super-hydrophobic surfaceswith pinecone-likehierarchical structures[20]arebeingdevelopedtoavoidcorrosion,recent trendsare focusedonthe developmentofnewmagnesium alloys based on materials including microscale reinforce- mentstoovercometheirmechanicalandphysicallimitations.
Somestudieshaveshownthatmagnesiumpropertiesare improvedbythe incorporationofsubmicrometrereinforce- ments. Oxides, nitrides, borides or metal carbides [18]are considered assomeofthemostpromisingreinforcements;
TiC showsparticularpromise[21,22].Thetypeofsynthesis method canalso affect thefinal properties [23]. Therefore, thepreparationofthesenovelmaterialsgeneratestheneces- sitytoanalysetheirfinalmechanicalandphysicalproperties.
Nevertheless, studiessurrounding magnesium-based mate- rials including submicrometre-sizedreinforcementsfor the transportsectorareveryscarceand,accordingtotheauthor’s knowledge,thereisnoliteraturedatasimultaneouslyinclud- ingatechnicalandenvironmentalevaluationofthematerials andproductionprocesses[24,25].Theenvironmentalanaly- sisconductedin thispaperfocusedon thelifecycle ofan exemplary component to be used ina gasoline passenger vehicle.Thecomponentwasfabricatedusingamagnesium alloy reinforced with submicrometre-scale particles of the Al/TiC mastercompoundcontaining60wt.%ofTiC.Tothis end,lifecycleassessment(LCA)wasthemethodologyapplied, whichisregulatedundertheISO14040standard[26].TheLCA methodologyallowstheassessmentofthepotentialimpacts associatedwithrawmaterialacquisition,viatheproduction, usephases,andwastemanagementinvolvedthroughoutthe lifecycleoftheproduct[27,28].
As mentionedbefore, anevaluationofthe environmen- tal impacts associated with the manufacturing of vehicle components using the magnesium alloy reinforced with submicrometre-scale particles wasperformed. This assess- mentwascarriedoutthroughaLCA)methodology,whichis usefulforassessingimpactsalongthelifecycleofaproduct, whichbroadensthescopeoftheenvironmentalanalysis[29].
TheRECIPEmethodwasusedtoclassifytheenvironmental impactsintothemostrepresentativemidpointcategoriesof theentiremanufacturingprocessandtheresultswerecom- puted usingtheSIMAPROv.8software.Theseare midpoint indicatorsevaluatedusingtheRECIPEmethod.Midpointindi- catorsareconsideredtobepointsinthecause–effectchain (environmental mechanism)ofaparticularimpactcategory somewherebetweenthestressorandendpoints.Forsuchmid- points,thecharacterisationfactorscanthereforebecalculated
toreflecttherelativeimportanceofanemissionorextraction inalifecycleinventory(LCI)byenvironmentalmetrics[27].To developtheLCA,theproductionprocessesofbothaluminium andmagnesium havebeenconsidered.Bauxite,aluminium hydrate,andaluminiumoxidearethemainrawmaterialscon- sumedinaluminiumproduction,withbauxiteasthemain resource(upto85%)[30].Anoverviewofthetypicallifecycle ofanaluminiumprocesshasbeenreportedbytheEnviron- mentalProfileReportfortheEuropeanAluminiumIndustry [31].Basedontheschemetoproducealuminiumproposedby thatreportandadditionalspecialisedliterature,aswellasarti- clesandreports,significantvariableswerecollectedtocreate acompletedatabaseforenvironmentalmodelling.
The majority ofthe world’s magnesium is produced in China and the main process used is the Pidgeon process, which has improved in efficiency over the past few years [32].ThisprocesshasbeenwellcharacterisedbyEhrenberger, whoperformeddatacollectionbasedonproductionstatistics andfuelconsumptionbytheChineseMagnesiumAssociation (CMA)providedbymagnesiumproducers[33].Duetothefact thatup-to-dateandreliabledataandresultsformagnesium productionareprovided,thelifecycle inventoryofmagne- siumproductionbythePidgeonprocessisaccountedforfrom Ehrenberger’sworktocreateacompleteLCIfortheenviron- mentalmodellingofthisstudy.
Moreover,another scenarioforprimarymagnesiumpro- duction addressing the typical process carried out by a Norwegian producer has been considered. This was the world’slargestmagnesiumproducerinthe1990s.Although thisfacilityinPorsgrunn(Norway)wasclosedinearly2000, this isthe mostrepresentative plant forthe productionof primarymagnesiuminEurope.
Here,magnesiumisproducedfromseawateranddolomite.
TheprocessstartsbyproducingMg(OH)2fromcalcinationof dolomitebymixingwithseawaterfollowedbytheprecipita- tionandfiltrationofMg(OH)2.Thefiltercakefromthelatter processthenundergoescalcinationtoproduceMgO.Chlorina- tionofMgOallowsMgCl2tobeobtained,whichiselectrolysed andeventuallyingotsareproducedinthefoundry.
Thus,theLCIformagnesiumproductionwasbasedonthe environmentalreportsofNorksHydrofortheyear1998,con- tainedinthedatabaseoftheSimaProsoftwareversion8.0(not shownhereduetoconfidentialityissues).
Finally,thereisoneothersignificantimpactfactorinthe processesformagnesiumalloyproduction.Magnesiumalloy productionneedsacovergastopreventdegradationfromcon- tactwiththesurroundingatmosphere.Twogasesareusually used,SF6andSO2.TheChinesePidgeonprocessusessulphur orfluxescontainingsmallamountsofsulphurtopreventthe magnesiummeltfromburning[34].However,SF6contributes asignificantenvironmentalburdenintermsofCO2eq.,asthis gasisconsideredaGHG.Therefore,theprocesssuchasthatin theNorwegianplant,assumedintheenvironmentalmodelof thisstudy,considersanalternativegascover,namelyR134gas, whichisconsideredanenvironmentally-friendlyprotection gaswithreferencetocastmagnesium.
Thus,thisstudyaimstofillpartofthisinformationgapby atechnicalandenvironmentalevaluationofsubmicrometre- sized particles basedon TiC asan approachforimproving the mechanical properties of magnesium alloy to produce
automotive components. An Al/TiC master compound containing 60wt.% of TiC was produced through a self- propagating high-temperature synthesis (SHS) process and embedded in a magnesium alloy by a mechanical stirring method.Thetechnicalevaluationwasconductedbyanalysing themostrepresentativephysicalandmechanicalproperties.
To this end, X-raydiffraction (XRD)and scanning electron microscopy (SEM)techniques were used toinvestigate the natureandpurityoftheTiCparticulatesinthematerialand theirsizes.Themechanicalproperties,namelyyieldstress, tensilestrength,andductility,weretestedfollowingtheASTM E8/E8M-13astandard.
2. Experimental techniques and
methodology for the environmental evaluation
2.1. MaterialpreparationForthepreparationofthemagnesiumcompositereinforced withTiCparticulates,anAl/TiCmastercompoundcontaining purealuminium andTiCparticles waspreparedand added tothemoltenmagnesiumalloy.Themastercompoundwas preparedbyanSHSreactionoftheAl-Ti-Csystem.
Topreparethemastercompound,thefollowingmaterials wereused:aluminiumpowder(suppliedbyPometonEspa ˜na S.A.withapurityof99.5%andaverageparticlesizelowerthan 200mm), titanium powder(witha compositionof Ti99.7%, C 0.1% max.,and Fe 0.2% max. providedby William Row- landLtd.withanaverageparticlesizelowerthan25mm)and blackcarbonpowder(withapurityof99.5%,averageparti- clesizelessthan1mmprovidedbyDegussa).Subsequently,in ordertopreparethemagnesiummatrixcomposite,thismas- tercompoundwasaddedinpowderformtoamoltenAM60 magnesiumalloy.ThisalloywassuppliedbyDeadSeaMagne- siuminIsraeliningotshape,containingawt.%of6.0Al,0.36 Mn,0.1Zn,andMg(Balance).
Detail description about the preparation of the Al/TiC master compound and magnesium alloy reinforced with submicrometre-sized particles, mechanical property tests, andmaterialcharacterisationaregivenbelow.
2.1.1. Al/TiCmasteralloypreparation
Titaniumand carbonpowderswere mixedinamolarratio ofTi/C=1.0and40wt.%ofAlpowderwasaddedtothissto- ichiometricmixture.Thiswasthen drymixedfor4husing a ball mill, beforebeing uniaxially cold pressed ata pres- sureof100MPausingahydraulicpressandastainlesssteel die.Acylindricalcompactwithapproximately60%theoret- icaldensity wasobtained.Toinitiate theSHS reaction,the compactwaslocallyheatedusingacurrentof16Vfor5s.Sub- micrometreTiCparticulateswithasizerangeof300–500nm wereformedinanaluminiummatrixthroughanSHSreaction.
2.1.2. PreparationofAM60samplesreinforcedwith submicrometre-scaleparticles
For the preparation of the particle-reinforced magnesium composite,astircastingmethodwasemployed.Thismethod consists of mechanically stirring the molten alloy until a vortexisgenerated,intowhichthereinforcingparticlesare
subsequentlyadded.Themastercompoundcompactwasfirst ball-milledfor8hinordertoreduceitssize.Approximately 1700gofAM60alloywerethenintroducedinasiliconcarbide crucibleandheatedinahigh-frequencyinductionfurnace.A k-typethermocouplewasintroducedinthecrucibleinorderto measurethetemperatureofthemoltenalloyandstabiliseitat approximately700◦Cforthestirringprocess.Oncecompletely liquid,andafterthedrosslayergeneratedinthesurfacewas removed,agraphitestirrerwasintroducedinsidethecrucible, veryclosetothebottomsurfaceofthecrucible.Themolten alloywasstirredat360rpmandthemastercompoundpow- derwasmanuallyaddedintothevortex.Thestirringwasthen maintainedfor10min. Finally,the stirrerwas stoppedand removedfromthecrucibleandthemoltenmaterialwascast inanironmould. Oncecompletelysolid,the castpartwas demouldedinordertobecharacterised.
2.2. Characterisationofmagnesiumalloyreinforced withsubmicrometre-sizedparticles
2.2.1. Physicalproperties
XRDandSEMwereusedtocarryoutthemetallographicanaly- sisofthecastsamples.Asmallsamplewascutfromeachcast partandthesurfaceofthesamplewaspreparedbygrinding throughgritpapersofvarioussizesfollowedbypolishingwith diamondpaste.
ThesurfacemorphologywasinvestigatedbyusingSEM, modelJEOLJEM5910LV,equippedwithanenergy-dispersive X-rayanalyser(EDX)tomakeasemi-quantitativeanalysisof thecompositionofthedifferentphasesofthesample.
TheXRDpatternwasrecordedonaBrukerD8ADVANCE withCuKaradiationandastepsizeof0.02◦.TheDiffractplus EVAsoftwarewasusedtoidentifythecrystallographicphases present.
2.2.2. Mechanicalproperties
Fromthecastparts,tensilespecimensweremachinedinorder tobetensiletestedatroomtemperaturefollowingtheASTM E8/E8M-13a standard;forthesetests,anINSTRONmachine wasused.Thespecimenwasmountedinthemachineand testedatacrossheadspeedof1mm/min.Thestrengthand elongationwerecontinuouslyrecorded.Sixspecimenswere testedforboththeTiC-reinforcedmagnesiumalloyandthe unreinforcedalloy.
2.3. Environmentalanalysisofanautomotive componentbasedonmanufacturingofmagnesiumalloy reinforcedwithsubmicrometre-sizedparticles
LCAmethodologyconsidersfourmainphasestoprovideguid- anceforgreaterconsistencyandqualityassurance,whichare brieflyoutlinedinFig.1.
2.3.1. Scopeoftheenvironmentalanalysisandfunctional unit
Inthisstudy,whichconcernsvehiclecomponents,theiden- tification of a lightweight material that exhibits improved mechanicalpropertiesisafeasiblegoal.Firstly,the evalua- tionwasperformedbythequantificationoftheenvironmental impacts oftwosteps, alloyproduction andthe die casting
Fig.1–MainphasesofanLCAstudy.
Fig.2–Overviewofmagnesiumlifecycleformanufacturingtransportapplication.
Table1–Environmentalimpactindicatorsstudied.
Impactcategory Unit
Climatechange kgCO2eq.
Ozonedepletion kgCFC-11eq.
Terrestrialacidification kgSO2eq
Freshwatereutrophication kgPeq.
Marineeutrophication kgNeq.
Humantoxicity kg1,4-DBeq.
Photochemicaloxidantformation kgNMVOC Particulatematterformation kgPM10eq.
Terrestrialecotoxicity kg1,4-DBeq.
Freshwaterecotoxicity kg1,4-DBeq.
Marineecotoxicity kg1,4-DBeq.
Ionisingradiation kBqU235eq.
Agriculturallandoccupation m2a
Urbanlandoccupation m2a
Naturallandtransformation m2
Waterdepletion m3
Fossildepletion kgoileq.
process.Secondly,theusephasewasalsoconsideredcalcu- latingtheCO2equivalent(CO2eq.)savingduringthelifetime ofacarusingalightcomponent(seeFig.2).
Themethodologicalframeworkofthisstudyincludesthe impactmidpointsindicatorsdescribedinTable1.Thefunc- tional unit isdeclared as onefinal part ofthe component evaluated(genericbody-jointcomponent).
2.3.2. Systemdescriptionandboundaries
Inordertoincluderelevanteffectsduringthelifecycleofthe reinforcedmaterial,acradle-to-gateapproachwaschosenfor thefirstanalysis,consideringtowcasesinvolvinglightweight alloyswiththeaimofcomparisonbetweenaluminiumalloys, asreference,andmagnesiumalloy.Theconsequenceofthe fuelsavingscausedbythelightweightmaterialusagewere
carried out as a secondary analysis. The boundaries are depictedinFig.3.
2.3.3. Lifecycleinventory(LCI)
TheanalysisfortheLCIwasdividedinto twolevels.Firstly, a background analysis containing secondary standardised data, usedinthemodelsforallthe lifecyclestepsinclud- ing allupstream processes, toprovideenergyandmaterial inputsformagnesiumandaluminiumproduction(described in the introduction section). Secondly, a foreground analy- sis, containing primary detailed data. The latter considers therelevantinputsandoutputsassociatedwiththediecast- ingprocessestoproducethecomponentreinforcedwiththe submicrometreparticles.Allenvironmentalmodelswereper- formedusingSimaProv8.0software.
2.3.3.1. Backgroundanalysis:Metalproduction. Forthisanal- ysis, a consistent in-house database, comparable with commercialdatabasessuchasecoinventversion3,wasused toprovidethemostrelevant,reliable,transparent,andacces- sibleLCIsecondarydata.Theanalysisstartedwiththedata showninFig.4,whichshowsthattheprimaryproductionof aluminiumandmagnesiumisdominatedbyChina.Itcanbe seenthatin2012Chinaproduced75%and34%oftheglobal magnesiumandaluminiumintheworld,respectively.More- over,theproductionofprimarymagnesium(2012)isconfined toonlytencountries[35,36].ItseemsthatnoEuropeancoun- triesarecurrentlylistedamongthemainprimarymagnesium producingcountries.
Thesedatacannotbeoverlooked,sincetheanalysisofthe lifecycle dependssignificantlyon primaryproductionallo- cation. In particular, this depends on the available energy sources in each country, which significantly influence the preparationofacompletedatabaseabouttheprocessforpro- ductionoftheaforementionedmetals.Thus,thetechnology
Fig.3–Descriptionofthesystemboundariesinthestudyoflifecycleforthepassengervehiclecomponentfabricatedusing magnesiumalloyreinforcedwiththesubmicrometreparticles.
Fig.4–Productionofmagnesium(left)andaluminium(right),2012[26,27].
forenvironmentalmodelling assumedinthis study isper- formedconsidering the standardaluminium technologyin Europeforprimaryproduction.
Nevertheless,incaseofmagnesium,themaintechnologies acrosstheglobeshouldbeconsidered.Therefore,twoscenar- iosfortheprimaryproductionofmagnesiumweretakeninto accountinthisstudy;thefirstconsistingofthemainprocess forproducingmagnesiuminChina,namely,thePidgeonpro- cess,andthesecondamagnesiumproductionplantbasedon electrolysisfromresourceslikeseawateranddolomite[37].
Theauthorshaveconsideredthesetwoscenariosbecause ofthemarkeddifferencesbetweenthetwoproductiontech- nologiesforprimarymagnesium.Toaidunderstanding,abrief descriptionoftheproductionprocessesconsideredforthese twometals(AlandMg)andtheiralloyingaredescribedinthe introductionsection.
2.3.3.2. Foregroundanalysis:Diecastingprocesstoproducethe AlandMgalloycomponents. Diecastingistheprocessanal- ysed toproduce the component eitherwith aluminium or magnesiumreinforcedwiththesubmicrometreparticles.Itis amanufacturingprocessnormallyfeaturingtwofurnaces,a meltingandholdingfurnace.Thesolidmetalismeltedinthe
meltingfurnace,beforebeingtransferredtotheholdingfur- nace,inwhichthetemperatureiskeptconstantwithalower powertoavoiditssolidification.Themoltenmetalistrans- ferredfromtheholdingfurnacetoashotsleeveinorderto beinjectedintothediecavityunderahighpressuretoobtain thedesiredcasting[38].Theprocessincludesmachiningand coolingstages(additionalstages)afterthesolidificationstage, inwhichthepartisdeburredinordertoremoveexcessmetal.
Theremainingmetalcanbemeltedagaininfuturecycles.
Inordertocomparethemagnesiumdiecastingwiththe aluminium process,the materialsand energybalancewere calculatedforthefunctionalunit.Inbothcases,theweightof thecomponentisthereferenceflowusedintheenergyand materialflowmodel.Theweightswere1.85kgand2.85kgfor themagnesiumandaluminiumcomponents,respectively.
Moreover,itisimportanttohighlightthatthereinforced magnesiumdiecastingprocesshasanadditionalstage(see caseAinFig.3),whichisthesystemmixing.Therefore,this and theAl/TiCsynthesisstagewere takenintoaccountfor the LCI. Detailed information about the LCI is not shown here because of confidentiality issues, however the main magnesium LCIdatareferredtoforthefunctional unitare summarisedinTable2.
Table2–Maininputsandoutputsrelevantforenvironmentalanalysisofthediecastingmagnesium.
Functionalunit=1productfinalpart=1.85kg
Inputs
Alloymagnesium(AM60) 2.1 kg/unit
Al/TiCmasteralloy 0.0325 kg/unit
Annualwater 4.9×10−4 m3/unit
N2 1.84×10−4 m3/unit
SO2 3.60×10−6 m3/unit
Outputs
N2 1.8×10−4 m3/unit
SO2 3.6×10−6 m3/unit
Produceddross 0.011 kg/unit
Dirtyaluminium 0.0013 kg/unit
Finalproduct 1.85 kg/unit
Water 4.9×10−4 m3/unit
Energy
Meltingandpre-heatingfurnace(Electricity) 1.1 kWh/unit
Holdingfurnace(Electricity) 0.8 kWh/unit
SHSprocess(Electricity) 0.2 kWh/unit
Mixingsystem(Electricity) 0.5 kWh/unit
2.3.4. SavingscalculationofCO2eq.
Avehicleusingpartsfromlightweightmaterialscanhavea reducedweightandthereforesavefuelduringvehicleoper- ation.ThisresultsinadirectreductioninCO2eq.emissions duringvehicleoperation.EmissionsofCO2 andotherGHGs decreaseinproportiontothedecreaseinfuelconsumption.
Itisworthnotingthatthisdoesnotapplytootheremissions, suchasparticlesornitrogenoxides,becausethedevelopment ofemissionsprovokedbyfuelsavingsisambiguous.
Thus,the equation shown below,based on the work of KofflerandRohde-Brandenburger[39],hasbeenusedforcal- culatingthefuelsavinginthisstudy.
Savedfuel=(m−mref)×R×0.01 (1)
Thesavedfuelhasunitsoffuelsaving[l/100km],mand mrefarethemassesofthealternativeandreferencecompo- nentsinkg,respectively.TheconstantRisthefuelreduction coefficientexpressedinunits[l/(100km×100kg)].Thevalue ofthefuelreductioncoefficientisalsobasedontheworkof KofflerandRohde-Brandenburger[39].Theyreportedavalue of0.35l/100kmbasedonthestandardnewEuropeandriving cycle(NEDC)forpassengercars.Thisparameterisimportant, sinceitreflectstheimplicationsintermsofenergyefficiency oftheuseofthemagnesiumcomponentinanoptimisedvehi- cle.Accordingtotheaforementionedauthors,theparameterR includessecondarymeasureswhentheenergyconsumption iscalculatedbasedontheNEDC.
2.3.5. Cut-offcriteria
Thefollowingcut-offcriteriawereusedintheenvironmen- talanalysistoensurethatallrelevantenvironmentalimpacts wererepresentedinthestudy:
(i) Materials:flowsoflessthan1%ofthecumulativemass ofalltheinputsandoutputsoftheLCImodel,depending onthetypeofflow,wereexcludedbecausetheirenviron- mentalimpactisnegligible.
(ii) Energy:flowsoflessthan1%ofthecumulativeenergyof alltheinputsandoutputsoftheLCImodel,dependingon thetypeofflow,wereexcludedbecausetheirenvironmen- talrelevanceisnegligible.
However,itwasensuredthatthesumofneglectedmaterial flowsdidnotexceed5%ofthemass,energy,orenvironmental relevance. These criteria were establishedbased on an in- depthanalysisofthesystemusingtheoperationalenergyand massbalancesfortheprocessesinvolved.
3. Results and discussion
3.1. TechnicalevaluationTheresultsobtainedinthetensiletestsconfirmthebenefitsof addingthesubmicrometreTiCparticulatestothemagnesium alloy. Theaddition of1wt.% ofparticles leads toimprove- mentsof11%and18%intheyieldstressandultimatetensile strengthvaluesrespectivelyand30% inthe ductilityofthe material.Themicrostructuralanalysisshowsthepresenceof
somesmallTiCaggregatesbutthebalanceoftheeffectofthe presenceTiCparticulatesispositive.TiCparticulatesappear both inthe centre ofthe aluminium grainsand the inter- granularregionandshouldcontributetostrengthenthealloy byhinderingthemovementofdislocationsthroughtheHall- Petcheffectrelatedtothedecreaseinthegrainsize,Orowan effectandtheincreaseinthedensityofdislocationsduringthe solidificationstageduetothecoefficientofthermalexpansion (CTE)mismatchoftheAM60matrixandTiC.
3.1.1. Materialcharacterisation
TheproductionofthefinalreinforcedAM60/(TiC1wt.%)mate- rial wascarriedout intwostages.Firstly,productionofthe Al/(TiC60wt.%)masteralloybySHSandsubsequentlyproduc- tionoftheAM60/(TiC1wt.%)reinforcedalloybystircasting.
Following the microstructures ofthe materialsobtainedin eachstageareshownanddiscussed.Fig.5showsthephysical aspectofthematerialobtainedaftertheSHSprocess.
3.1.1.1. Characterisation of Al/TiC master compound. Fig.6a shows the microstructure of the Al/TiC (30:70) compound obtained bySHS inthe preliminarytrials. TiC particulates appearasroundparticulatescoatedandsurroundedbypure aluminiumthatispresentin30wt.%.Themicroscopyobser- vationofthesamplesshowsthattheself-propagatingreaction hastakenplacecorrectlyandthereisneitheranypresenceof looseTiorCparticulatesnoranysecondaryproduct.
ThesizeoftheTiCparticulatesrangesfrom0.5upto7mm.
ThesurfaceofTiCparticulatesisclean.Particulatesarewell wettedandappearcoveredbyaluminium.Furthermore,there isnotanyclueofothersecondaryreactionsthatcouldlead totheformationofTiAl3orAl4C3particulates.Theseobser- vations are furtherconfirmed with the results ofthe XRD analysis(seeFig.7)whereonlyAlandTiCappear.Nonetheless thegoaloftheworkwastoproducesubmicrometre-sizedTiC particlesandthereforetheprocesstoobtainasecondgener- ationofparticulateswasdeveloped.
Fig.5–Al/TiCmasteralloyproducedbySHScontaining 40wt.%ofpurefreealuminiummanuallycrushedbefore theballmillingprocess.
Fig.6–(a)ScanningelectronmicrographofAl/TiCpowdersina30/70ratio.ThesizeoftheTiCparticulatesrangesfrom0.5 upto7mm,(b)ScanningelectronmicrographofAl/TiCpowderwithTipowderof106and45mm,(c)Scanningelectron micrographofTiCsampleshowingsubmicrometre-sizedparticlesproducedbySHSmixedwithlargeparticulates.
3.1.1.2. Development of the second generation of submicrometre-sized TiC. Two different approaches were tried toachieve submicrometre-sized TiC particles.On the onehand the use ofelementalTi powders havingsmaller sizesandontheotherhandtheaccelerationofthesolidifi- cationstageimmediatelyaftertheendofthecombustionin theSHSprocesssothattheparticlescouldnotcoalesceand growwithinthereactionchamber.
Previous experiences accumulated by the authors had shown that the size of the initial powder of Ti used in the SHS reaction could have a direct influence on the size ofthe TiC powders obtainedafter the process. When using Ti powder with a size of 150mm the average size of TiC particulates was around 1.5mm (see Fig. 6a). The size decreased down to 0.5–5mm when Ti powders of
106mm were used (see Fig. 6b) and this size got further decreased with smaller Ti grain sizes0.3–3mm. Even so it was also observed that the difference of the TiC particu- latesobtainedwithTipowdersof45and25mmwasminimal and therefore the size of 45mm was selected for further tests.
Resultsofthesecondapproachtodecreasethecoolingtime ofthereactionandconsequentlythesizeofTiCparticulates areshownnow.Differentmethodsweretestedtoimplement thisconcept,theapplicationofcompressedcoldairandargon intothereactionchamberandincreasingthealuminiumcon- tentintheinitialmixtureofreactants.
Theformershowedtobedifficulttoimplementandfur- thermoredidnotprovideanyapparentdecrease inthe TiC particulates.Itwasdifficulttoknowtheprecisemomentof
Fig.7–XRDpatternofAl/TiCpowders.
theendofthereactionandthereforewhentointroducethe coldfluidintothechamberwithoutdisruptingthesynthesis.
Theincreaseintheamountofaluminiumintheinitialmix- tureofTi,CandAlpowdersresultedinabetterapproach.It wasseenthatthehigherthealuminiumcontentthesmaller thesizeoftheTiCparticulatescreated.Thisisthoughttobe relatedtotheincreaseintheheatdissipationcapacityofthe mixtureaswellasthedecrease inthe numberofTiandC atomsavailablethatmaydiffuseinto theTiCnucleiduring thereaction.Thisoptionhadaclearlimitthough.Abovean amountof40%ofaluminiumpowdersintheinitialmixture, thereactionbetweenTiandCwasnolongerauto-propagated andtheSHSsynthesisdidnotproceedcorrectly.Eventually, themasteralloywaspreparedintheconditionsthatledtothe lowestTiCparticulatessize,i.e.byusingTipowderof45mm andbyincorporating40%ofaluminiumintotheinitialmix- tureofTiandblackcarbonpowders.Fig.6cshowsatypical microstructureoftheobtainedpowders.Smallandlargepar- ticulateswithdifferentshapesmaybeseenbutmostofthe TiCparticulatespresentasphericalshapeandsizelowerthan 500nm.
Ascan beseen inFig. 8, the study ofthe sizedistribu- tionofthesamplesconfirmedthatmostoftheparticulates weresubmicrometre-sizedeventhoughthepresenceofpar- ticulateslargerthan1mmmaybeappreciated.47.3%ofthe particulates presented a size lower than 500nm and only 22.4%oftheparticulatesarebiggerthan1mm.
3.1.1.3. MicrostructureoftheTiCreinforcedmagnesiumalloy.
Fig. 9 shows SEM imagesof the microstructureof the TiC reinforced magnesiumalloy. Itis appreciatedthat the bor- der betweenthe metaland the particulatesisclean, there seemstobenotanychemicalreactionbetweenbothphases.
Individualparticulatescanbeseenbothatthegrainbound- ariesandwithinthegrains.Therearealsosmallclustersthat arelocatedintheboundariestogetherwithothertypicalsec- ondaryphasesofthealloy.Stircastingprocessisknownto help disperse ceramic particulates within the liquid metal butitmayalsocreateporosityanddefectswithinthemelt.
Fig.8–Sizedistributionof“secondgeneration”TiC particulatesobtainedwithTipowderwithanaveragesize of45mmand40%ofaluminiumintheinitialmixtureof Al/Ti/C.
Theexistenceofagglomerationsandincreaseofporosityis thoughttobethemainreasontoexplainthelossofproper- tiesappreciatedwhentheincorporationofmorethan1wt.%
particulatesistried.Infact,the improvementofproperties shown by the samplescontaining 1wt.% ofparticulates is reallylowincomparisonwiththesamplewithonly0.2wt.%.
TheAM60+TiC0.2wt.%samplespresentanincreaseof5%in yieldstress,10%inUTSandupto30%intermsofductility whencomparedtothereference non-reinforcedalloy:This increaseismuchlimitedwhenhigherTiCcontentsaretried tobeincorporated.
3.1.2. Mechanicalproperties
Table 3 provides the results of the tensile tests of speci- menscontainingAM60alloyanddifferentpercentagesofTiC particulatesincorporatedtothematrixthroughthestircast- ing process.Results ofnon-reinforcedAM60 alloyobtained
Fig.9–SEMimagesofthemicrostructureoftheTiCreinforcedmagnesiumalloy.
Table3–MechanicalpropertiesofsubmicronreinforcedAM60alloy.Standarddeviationvaluesareprovidedin parenthesis.
Materialsa Yieldstress(MPa) Ultimatetensilestrength(MPa) Elongation(%)
AM60(reference) 106.25(20.81) 193.00(34.26) 7.25(3.23)
AM60+TiC0.2wt.% 111.67(4.95) 214.67(24.26) 9.67(2.83)
AM60+TiC1wt.% 118.00(10.50) 227.00(6.00) 9.43(0.46)
AM60+TiC1.5wt.% 109.27(17.76) 200.05(26.34) 6.50(2.87)
a Allsamplescastbygravitycastingat700◦Cintoametallicmould.
withthesame mouldand castingparametersare provided forcomparisonpurposes.
Theanalysisofthevaluespointsoutthattheadditionof TiCparticulatesprovidesandimprovementofpropertiesas foreseen.Addingonly0.2%ofparticulatesleadstoanincrease inaround5%inthemechanicalstrengthand30%intheduc- tilityofthealloy.Themechanicalstrengthfurtherincreases whenthe amount ofparticulatesisincreasedupto 1wt.%
eventhoughtheductilityvaluepresentsaslightdecreaseand thesamplescontaining1.5wt.%ofTiCpresentworseresults, evenlowerthan thoseobtainedwith0.2wt.%.Ontheother hand,theanalysisofthemicrostructuresshowsthattheTiC particulatesinduceadecreaseinthesizeofthemagnesium grain. Theseresultsareinagreementwithworksbasedon submicrometreandanoreinforcedmagnesiumalloys.
In contrast to composites with particulates larger than 1mm,theductilityofthematerialseemstoincrease.Thepres- enceofTiCparticulatesleadstoadecreaseinthegrainsize andintroducestressfieldsduetothemismatchinCTE.They mayalsoactasbarrierstothemovementofthedislocations throughthe phenomenonknown asOrowanstrengthening that explains that dislocationscannot advance dueto the presenceofwelldispersedhard phasesthatmust beover- passedandthereforeactasbarrierstotheirfreemovement.
Thepresenceofthedispersedparticlesmayalsoinducethe creationofcleavagecracksthatmaydissipatestressconcen- trationsnearthecrackfront.
ThesepositiveeffectsseemtofadewhenthecontentofTiC particulatesovercomes1wt.%.Thismayberelatedtoporosity ofthesamplesduetotheincorporationofoxidesduringthe stircastingprocessofsuchcomposites.
3.2. Environmentalanalysis
3.2.1. EvaluationofcasestudyA:component manufacturingbasedonmagnesiumalloy
Table4showsresultsconcerningtheenvironmentalimplica- tionsassociatedwiththealloyproductionstage.Ontheone hand,itcanbeseenthatinmostofimpactindicators,thepro- cesstoproducemagnesium(Pidgeon)hashigherpercentage
when compared to the process carried out in the Norwe- gianplant.Inparticular,theclimatechangecategoryshows ahigherimpactinthecaseofmagnesiumproductionbythe Pidgeonprocess.Thisresultcanbeassociatedwiththesource ofenergyrequiredforthePidgeonprocess.Fig.10showsthe networkforbothprocess(NorwegianplantandPidgeonpro- cess)containingthestepsthatcontributetothetotalCO2kg eq.Inordertohighlightthemainproduct,thenetwork’sprod- uctsarepartiallyshownwithacut-offofnodebelow0.6%.
Thus,itcanbeobservedthatmaincontributionforboth processesisfocusedontheelectricityproductionwherethe maindifferenceintermsofCO2eq.canbefoundinthispoint.
Thisiscorroboratedwhentheclimatechangecategoryofelec- tricityproductionforbothroutesarecomparedandevaluated bythesamemethodsofarused(RECIPE).TheCO2eq.emis- sionperkWhofthePidgeonprocessis3timeshigherthan thatemittedbytheNorwegianplant,whichleadstohigher impactintermsoftheclimatechangecategory.
The result above is consistent with the results of the study carried out by Simone et al. [33,40], which mention thattheemissionsfromupstreaminthePidgeonprocessare attributedtotheenergy-intensive production.Inparticular, ferrosilicon(FeSi)isconsideredtobethelargestcontributor tooverallemissionssinceahighamountenergy(electricity) isusedforitsproduction.Theseauthorsalsoconcludethat whentheprimarymagnesiumisobtainedfrom electrolysis process,lessGHGareemittedwhencomparedtothePidgeon process.
Asimilaranalysiscanbeappliedtothealuminiumpro- ductionprocesstoexplainwhyitreflectslowervalueofCO2
eq.whencomparedtobothprocessestoproducemagnesium previouslystudied.AsthemagnesiumproducedbytheNor- wegianplantshowstohavearound65%ofindicatorslower thanaluminiumproductiontechnology,themagnesiumtech- nologythroughtheelectrolysismethodisthemoresuitableto obtainthislightmetaltobeusedinthecomponentmanufac- turing.
Basedon this premise,the magnesium throughNorwe- gianplanthasbeenconsideredforenvironmentalmodelling ofthemagnesiumcomponentmanufacturing.Thus,andas
Table4–Resultsonenvironmentalimpactfortheprimaryalloyproduction(aluminiumandmagnesium).
Impactcategory Units Aluminium
production
Magnesiumproduction (Norwegianplant)
Magnesiumproduction (Pidgeonprocess)
Climatechange kgCO2eq 11.89 22.60 85.41
Ozonedepletion kgCFC-11eq 7.14×10−7 3.13×10− ◦ 5 7.24×10−7
Terrestrial acidification
kgSO2eq 0.047 0.025 0.126
Freshwater eutrophication
kgPeq 0.005 0.0006 0.009
Marine eutrophication
kgNeq 0.002 0.006 0.015
Humantoxicity kg1,4-DBeq 0.372 0.070 0.707
Photochemical oxidantformation
kgNMVOC 0.028 0.040 0.064
Particulatematter formation
kgPM10eq 0.023 0.008 0.043
Terrestrial ecotoxicity
kg1,4-DBeq 5.98×10−4 8.5×10− ◦ 5 4.31×10−4
Freshwater ecotoxicity
kg1,4-DBeq 0.002 0.0007 0.0030
Marineecotoxicity kg1,4-DBeq 0.007 0.001 0.005
Ionisingradiation kBqU235eq 3.040 0.412 0.745
Agriculturalland occupation
m2a 0.021 1.908 0.036
Urbanland occupation
m2a 0.025 0.022 0.165
Naturalland transformation
m2 −3.85×10−5 1.00×10−4 6.40×10−4
Waterdepletion m3 321.13 15.94 21.46
Fossildepletion kgoileq 0.017 0.002 0.120
observed in Fig. 11a, the manufacturing process of non- reinforced magnesium component shows greater CO2 eq.
(climatechangeindicator)whencomparedtothealuminium component.Thisresultisduetothemagnesiumalloypro- ductionwiththehigherenergyconsumption.Infact,when theenvironmentalmodellingwasanalysedforeachstage,the alloymagnesium productionphaseresultedtohavehigher environmentalburdenthanthediecastingprocessforallindi- cators(disaggregatedresultsarenotshownhere).
Nevertheless,theoppositeoccurs formostotherimpact indicators when comparing the magnesium component through Norwegian plant with aluminium. This corrobo- rates that magnesium would be a good candidate among lightweightmaterialsfortheautomotiveindustry.
3.2.2. EvaluationofcasestudyB:component
manufacturingbasedonmagnesiumalloyreinforcedwith submicrometre-sizedparticles
The results in previous section allow concluding that the process for magnesium alloy production has a significant influenceinthelifecycleofavehiclecomponentbasedon magnesium. Under this scenario, the environmental mod- elling described in this section also considers that the magnesiummetalproducedfromelectrolysismethodtobe usedinthemagnesiumalloy,since,theprocessformanufac- turingthecomponent,usingmagnesiumproducedbyNorks Hydro,wouldhavealowerCO2eq.emissionscomparedtothe Pidgeonprocess.
Thus, Fig. 11b depicts the environmental results ofthe three stages for vehicle component manufacturing using the magnesium alloy reinforced with submicrometre-sized
particles:Al/(TiC1wt.%)synthesisstage,themixingprocess andthecomponentmanufacturing.Firstly,itcanbeobserved thatthemixingsteprevealshigherpercentagesinallenvi- ronmentalcategories.Thisisconsistentwithresultsshown inprevioussection,since,themixingsystemstageconsiders theenvironmentalburdenduetothemagnesiumalloypro- duction stageand,asexplainedabove, this stageprovokes ahigh environmentalimpact.By contrast,thesynthesisof Al/(TiC1wt.%)shows lowerpercentagesalong theenviron- mentalindicators.
One may think that this is not the expected result, because of the use of submicrometre materials, such as submicrometre-sizedtitaniumcouldhaveimpactsinterms oftoxicity.Althoughelementaltitaniumisofaloworderof toxicity,laboratoryanimals(rats)exposedtotitanium com- poundsviainhalationhavedevelopedsmall-localizedareasof dark-coloureddustdepositsinthelungs.Moreover,anexces- siveexposureinhumans may leadtoneuro-inflammation, furtherbraininjurywithaspatialrecognitionmemoryand loco-motor activity impairment [41]. Thus, it is important tohighlight thatthe amountusedinthe magnesium alloy reinforced with submicrometre-sized particles is toosmall to determine the environmental implications through the methodology proposed in this study. In fact, in order to determinethe potentialenvironmentalriskscaused bythe use ofthese materials, afurther environmental modelling should be developed, in which, the environmental effects should be analysed by means of a particular LCA at sub- micrometre scale, taking into account the chemical and biologicalinteractionsofsubmicrometre-particleswiththeir surroundings.
Fig.10– NetworkofproductsthatcontributethetotalCO2eqofthemagnesiumproduction:(a)Pidgeonprocess(b) Norwegianplant.Inordertohighlightthemainproduct,thenetwork’sproductsarepartiallyshownwithacut-offofnode below0.6%.
Ingeneral,itcanbesaidthat,besidesthepositiveeffect oftheAl/(TiC1wt.%)onmechanicalproperties,theincorpo- rationofthesubmicrometreparticlesintomatrixmagnesium alloyhasalowenvironmentalimpactwhencomparedtoother stagesinvolvedinthemanufacturingprocessofthereinforced magnesiumalloycomponent.However,majortechnological progressesare neededtodevelopaprocess toproducepri- marymagnesiumwithminimumCO2emissionsconsidering evenamagnesiumrecyclingprocess.
3.2.3. ComparisonofcaseAandB
Aftertheanalysisofeachcasestudy,Fig.12showsthecom- parison of both cases, the environmental results for one component manufactured based on reinforced magnesium alloy (case A)and onecomponent manufactured basedon aluminiumalloy(caseB).
Asitcanbeseen,itisnotpossibletoconcludewhichcase studyismoreenvironmentallyfriendly,sincethisconclusion
would depend on the indicator analysed. Nevertheless, it canbesummarisedthatexceptfiveenvironmentalindicators (climate change, marine eutrophication, ionising radiation, agricultural land occupation and natural transformation), the rest reveal that the component manufactured using the aluminium alloy has ahigher impact when compared tomagnesium.Thedifferenceisparticularlyremarkablein case of freshwater eutrophication, human toxicity, terres- trial and marine ecotoxicity, where the impact associated with the reinforced magnesium component is approxi- mately lower 20% than the impact of the aluminium component.
Nevertheless,oneofthemainindicatorsthatareconsid- eredintheroadtransportistheclimatechange.Inthisstudy, the reinforced magnesium alloy hasahigher impact com- paredtothecomponentmanufacturingusingaluminium.For thatreason,ithasbeennecessarytoconsiderincludingthe study oftheusephase,inwhich,thefuelsavingcausedby
Fig.11–(a)Resultsonenvironmentalimpactcategoriesfornon-reinforcedcomponentmanufacturing,(b)Environmental burdensassociatedwiththedifferentstagesofthecomponentmanufacturingbasedonmagnesiumalloyreinforcedwith submicrometre-sizedparticles.
thelightweightcomponent,canreducetheCO2eq.emissions andthereforedetermineifthehigherenvironmentalimpact associatedwiththemagnesiumcomponentmanufacturingis offset.
3.2.4. Usephasescenarioanalysis
AsobservedinTable4,theresultsshowthatmagnesiumpro- ductiontechnologiesleadhigherCO2eq.whencomparedto thealuminiumproduction,whichismainlyattributedtothe highenergyconsumptiongeneratingconsiderableGHGemis- sions.Therefore,thespecialinterestandcontributionofthis work is focusedinincreasing and broadening the applica- tionsofmagnesium(asalightweightmaterial)withimproved mechanicalpropertiesintheautomotivesector.
Itisknownthattheamountoffuelandemissionsavings duringtheusephasedependslargelyontheweightreduction
resultingfrom thematerialsubstitution.Thereby,fromthis basisofcalculationformbasedonthefuelconsumptionsav- ings,theabovestatementcanbeevidencedinFig.13.There thedifferencebetweenCO2eq.emissionsrespecttotheref- erencecomponentisdepictedversusthedrivenmillageofa carwithanassumedlifetimeof200,000km(thereferencecase showninthefigureisrepresentedasthealuminiumbaseline (dottedline)).Apointaround28,000kmcanbeobservedat whichtheCO2eq.emissionsarecompensatedwithrespect to thecomponent manufacturingincluding the production ofmetalalloy.Thispointcanbeconsideredasabreak-even point.
Fromthis point,theuseofalightweightcomponentled tonegativevaluesof1kgCO2 eq.,whichindicatesbenefits fromtheenvironmentalpointofview.Thisisanimportant result indicating that the use ofreinforced magnesium in
Fig.12– ComparisonoftheenvironmentalresultsobtainedforcaseA(onecomponentmanufacturedbasedonreinforced magnesiumalloy)andcaseB(onecomponentmanufacturedbasedonaluminiumalloy).
Fig.13– CO2eq.savingsintheusephaseofthegeneric bodyjointcomponentrespecttothealuminiumcomponent (Reference).
automotivecomponents notonlyimproves the mechanical properties,butitmitigatestheenvironmentalburdeninterms ofclimatechange.
The above results are comparable with the Simone et al.’s study [33]. They raise several scenariosforprimary magnesiumproductionbasedonsimilartechnologies,where their high environmentalburdensare compensated during theusestageofthevehiclecomponentmanufacturedwith magnesiumalloy.
Nevertheless,itisworthnotingthatobtainingabreak-even point atlowmileage drivendependsconsiderably ofinitial conditions.Inotherwords,theCO2eq.impactattributedto thecomponentmanufacturing(intersectionpointontheaxis ofordinates)willbeoffsetinareasonablemileagedepending ontheweightreductioninthevehiclebyusingamagnesium componentaswellasofthenoveltechnologyforitsmanu- facture.Thus,theenvironmentalburdeninitslifecycle(from cradle-to-gateincludingtheusephase)willbebalanced.
4. Conclusions
Thisstudyanalysedsimultaneouslythetechnicalandenvi- ronmental performance of a novel developed magnesium alloy reinforced with submicrometre-sized TiC particles to produce automotive components. The AM60/(TiC 1wt.%) master compound was produced through self-propagating high-temperaturesynthesis(SHS)processandembeddedin magnesium alloy bya mechanical method.In general, the studyshowedpositiveresultsinbothperspectives,thetech- nicalandenvironmentalevaluations.
On theonehand,the technicalevaluationanalysed the most representative physical and mechanical properties.
In case of physical properties, the results confirmed that duringtheSHSself-propagationreactionnopresenceofany looseofTiorCparticlesoranyothersecondarycomponents wasfound.Thesubmicrometre-sizedTiCproduction,agood sizedistributionoftheparticles(aswasshownbySEMand XRD analysis), wasachieved. Indepth, most ofthemwere
submicrometre-sizedlowerthan500nanometres(morethan 47%oftheparticles)andsphericalshaped.Only22.4%ofthe particlesobtainedwerebiggerthan1mm.Inaddition,results alsoconfirmedthegoodperformanceofthematerialsinceit wasshownthattheadditionofupto1wt.%ofTiCincreased 11%the yieldstress, 18%the ultimatetensilestrength and 30%theductilityofthematerialwithregardstothecaseof initialmagnesiumalloy.
Ontheotherhand,theenvironmentalevaluationrevealed thattheincorporationofthissubmicrometre-particleinto a matrix magnesium alloy had a low environmental impact whencomparedtootherstagesinvolvedinthemanufactur- ingprocessofthecomponent,inparticular,themagnesium production.Thislattershowedhighestenvironmentalimpact whencomparedtothealuminiumprocess,morethan70%of theindicatorsinthePidgeonmethod.
Nevertheless, comparing the final automotive compo- nent,madeofreinforcedmagnesiumthroughtheelectrolysis method using the alternative R134 gas cover, with the aluminium component, the resultsrevealed that the envi- ronmentalimpactassociatedwiththereinforcedmagnesium componentshowedlowerenvironmental(70%oftheindica- torsanalysed).
However,thiswasnotobservedinthecaseoftheclimate changeindicator,wheretheproductionofthereinforcedmag- nesiumcomponententailedhigheramountofCO2eq.thanin thecaseofthealuminiumcomponent(around90%).There- fore,thestudyincludedtheusephaseofthecomponentwhere the lower weight ofthis component resultsin fuel saving inthecarand,consequently,anassociatedreductioninthe CO2 eq.,which offsets the environmental impact interms of climate change induced in the magnesium production stage.
Conflicts of interest
Theauthorsdeclarenoconflictsofinterest.
Acknowledgements
The research leading to these results has been received fundingformtheEuropeanUnionSeventh FrameworkPro- gramme(FP7/2007-2013) under grant agreement n 314582 - EFEVEproject.Theauthorsthanktheprojectpartnersforpro- vidingsupporttothisresearch.
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