Al

Trans.NonferrousMet.Soc.China29(2019)1816−1823

MicrostructureevolutionofAl−Cu−Mgalloyduring

rapidcoldpunchingandrecrystallizationannealing

Ze-yiHU1,Cai-heFAN1,Dong-shengZHENG1,Wen-liangLIU1,Xi-hongCHEN2

1.CollegeofMetallurgyandMaterialEngineering,HunanUniversityofTechnology,Zhuzhou412007,China;

2.CRRCZhuzhouElectricLocomotiveCo.,Ltd.,Zhuzhou412007,China

Received31October2018;accepted30June2019

Abstract:ThemicrostructureevolutionofsprayformedandrapidlysolidifiedAl−Cu−Mgalloywithfinegrainsduringrapidcoldpunchingandrecrystallizationannealingwasinvestigatedbytransmissionelectronmicroscopy(TEM).Theresultsshowthattheprecipitatesoffine-grainedAl−Cu−MgalloyduringrapidcoldpunchingandrecrystallizationannealingmainlyconsistofSphaseandasmallamountofcoarseAl6Mnphase.Withtheincreaseofdeformationpasses,thedensityofprecipitatesincreases,thesizeofprecipitatesdecreasessignificantly,andthedeformationandtransitionbandsdisappeargradually.Inaddition,thegrainsarerefinedandtendtobeuniform.Defectsintroducedbyrapidcoldpunchingcontributetotheprecipitationandrecrystallization,andpromotenucleationandgrowthofSphaseandrecrystallization.Deformationandtransitionbandsinthecoarsegrainstransformintodeformation-inducedgrainboundaryduringthedeformationandrecrystallization,whichrefinegrains,obtainuniformnanocrystallinestructureandpromotehomogeneousdistributionofSphase.Keywords:Al−Cu−Mgalloy;microstructureevolution;precipitate;recrystallization;deformationband;rapidcoldpunching

1Introduction

Al−Cu−Mgalloyhasbeenwidelyappliedto

aerospaceandmilitaryindustriesbecauseofits

advantagesuchashighstrength,goodformabilityand

heatresistance[1,2].Precipitationstrengtheningand

grainrefinementarethemainstrengtheningand

tougheningmethods.UndertheconventionalT6-like

heattreatment,themainstrengtheningphasein

Al−Cu−MgalloyisSphasewithlowCu/Mgratios

(Al2CuMg)andθ'phase(Al2Cu)withhighCu/Mg

ratios[3−6].Deformationnotonlymakesthematerial

obtaingoodworkhardeningproperties,butalso

introducesalargenumberofdislocationsduringthe

deformation.Agingprocessafterdeformationcan

releasedeformationstress,promotethedispersive

nucleationandgrowthofprecipitates,andevenchange

thecharacteristicsandprecipitationsequenceof

precipitates[7−10].STYLESetal[11]investigatedthe

relationshipbetweenthedecompositionsequenceof

supersaturatedsolidsolutionandthephasein

Al−Cu−Mgalloy,andpointedoutthattheformationtimeofSphaseathighertemperatureismuchshorter

thanthatatlowertemperature.LIetal[12]investigated

theeffectofpre-deformationonthemicrostructureof

high-purityAl−Cu−Mgalloyandfoundthatthedensity

ofS'phase(Al2CuMg)increaseswhileitssizedecreases

withtheincreaseofpre-deformationdegree.YIN

etal[13]studiedthegrowthbehaviorofSprecipitation

phaseparticleswithinthegrainsofhighstrength

Al−Cu−Mgalloy.Itwasreportedthatthestructuralunits

intheGPBregionformedaroundSphaseathigheraging

temperature(above180°C)andhinderedthegrowthofS

phasealongthewidthdirection,resultinginthegrowth

ofSphaseintocolumnarcrystal.YANGetal[14]

studiedtheeffectofappliedstressontheprecipitation

processofθ'andSphasesinAl−Cu−Mgalloyandfound

thatappliedstresspreventedtheprecipitationofθ'phase

bychangingtheθ'/Sratioduringthecompetitive

precipitation,therebytheprecipitationofSphasewas

promoted.Itcanbeseenthatthemicrostructure

evolutionandphasestructurecharacteristicsof

Al−Cu−Mgalloyhavebeenstudiedunderthe

conventionaldeformationandagingtemperatures.

Inthepresentwork,thealuminumalloycartridge

Foundationitem:Project(2019JJ60050)supportedbytheNaturalScienceFoundationofHunanProvince,ChinaCorrespondingauthor:Cai-heFAN;Tel:+86-731-22183432;E-mail:369581813@qq.comDOI:10.1016/S1003-6326(19)65089-2Ze-yiHU,etal/Trans.NonferrousMet.Soc.China29(2019)1816−18231817

waspreparedbyrapidcoldpunchingand

recrystallizationannealing,basedonthesprayformed

Al−Cu−Mgalloywithfinegrains.Theprecipitation

phase,grainmorphologyandtheevolutionof

deformationbandduringrapidcoldpunchingand

recrystallizationannealingwerestudied.Theinteraction

betweenprecipitationphaseandrecrystallization,the

formationmechanismofdeformationbandanditseffect

ongrainrefinementwerediscussed.

2Experimental

Fine-grainedAl−Cu−Mgalloycylindricalbilletwas

preparedbysprayformingonaself-developedspray

formingdeviceSD380.Thechemicalcompositionofthe

alloyisshowninTable1.Thecylindricalbilletwas

extrudedintoroundbarwithadiameterof30mmbya

1250Textrudingmachineat723Kandtheextrusion

ratiowas15:1.Cylindersampleswith20mminlength

werecutfromthebarbywire-cuttingmachineandthen

placedinaself-designedstampingdie.Afterfourpasses

ofrapidcoldpunchingandrecrystallizationannealing,

thealuminumalloycartridgeswereprepared.The

schematicdiagramofrapidcoldpunchingisshown

inFig.1.Theprocessofrapidcoldpunchingand

recrystallizationannealingisshowninFig.2.In

thecaseofrecrystallizationannealing,thecorresponding

Table1ChemicalcompositionofAl−Cu−Mgalloy(wt.%)

CuMgMnSiFeAl

4.511.460.56<0.05<0.05Bal.

Fig.1Schematicdiagramsofrapidcoldpunching:a—Sample;