简介:ProblemsaboutsurfacemountingprocessforfinepitchdevicesandreasonsonsolderbridgingofLtypeleaddevicesweldedaredepicted.Bridgingmechanismandinfluencefactorsareanalyzedwithtwo-dimensionalgeometricmodel.Basedonthis,high-densitysurfacemounttechnology(SMT)forfinepitchLtypeleaddevicesheatedbyscan-ninglaserisraised.SurfacemountprocessforQFP208onprintedcircuitboard(PCB)isstudied.Theresultsoftestsarethatitisquitepossibletosolvethesolderbridgingofsurfacemountingforpitchdeviceswithscanninglaser-heat-ingmethod.
简介:ThediffusionbondingofAZ3\BMgalloyandQ235steelwasinvestigatedwithaZn-5AIalloyasinterlayerandunderdifferentholdingtimerangingfrom3to1200s.Themicrostructureandphasecompositionsofbondedjointswerecharacterizedbyscanningelectronmicroscopy(SEM),energydispersivespectrometer(EDS)andX-raydiffraction(XRD)methods.TheshearstrengthofMgalloy/steeljointswasmeasuredbytensiletester.Itwasfoundthatthemicrostructureofbondedjointsevolveddramaticallyalongwiththeprolongationofholdingtime.Undertheholdingtimeof3s,themainpartofjointwascomposedofMgZn2phaseanddispersedAl-richsolidsolutionparticles.Whenincreasedtheholdingtimemorethan60s,theexcessivesolutionofAZ3\Bintotheinterfacialreactionarealedtotheformationofcoarsephaseandeutecticmicrostructure,andalsothecomplexFe-AlandMg-Al-ZnIMCsattransitionlayerclosedtoQ235steelside.Accordingtothetensiletestingcharacterizations,thejointsobtainedunderholdingtimeof3sexhibitedthebestshearstrengthof84MPa,andthefractureoccurredattheintermediarypartofjointwheretheflexibleAl-richsolidsolutionparticlescouldhelptoimpedethemicrocrackpropagations.Withprolongingtheholdingtimeto600s,theshearstrengthofjointswasdeterioratedenormouslyandthefracturepositionwasshiftedtothetransitionlayerpartclosedtoQ235steel.
简介:ThevacuuminductionbrazingofSiCparticulatereinforcedLY12alloymatrixcompositeusingAl-28Cu-5Si-2Mgfillermetalhasbeencarriedout.Themicrographofthejointinterfacewasobservedbyscanningelectronmicroscopy.Thejointstrengthwasdeterminedbysheartests.Theresultsshowthatbrazingtemperature,holdingtime,SiCparticlevolumepercentageandpostheattreatmentinfluencejointstrength.SiCparticleshappeninthebrazingseamandthedistributionofSiCparticlesinthejointisnotuniform.Particle-poorzonesinthejointexistnearthebasemetal,andparticleconcentratezonesexistinthecenterofthebrazingseam.Inaddition,thefailureofthecompositeispredominantlyinitiatedbytherootingofSiCparticleinthebrazingseamandthemicro-crackexpandedalongthebrazingseamwithlowenergy.
简介:Intheacceleratordrivensub-criticalsystem(ADS)cooledbyliquidPbBialloy,theausteniticstainlesssteel316Lisoneofthecandidatesofstructuralmaterials.However,thecorrosionandwearbehaviorof316Lsteelinthehigh-velocitystreamofliquidPbBiisthemostessentialissue,whichisurgenttobepaidcloseattention.Inordertoacquirethemorphologyandmechanicalpropertiesof316Lsteelintheconditionsofdifferentrelativeflowingvelocity(RFV),respectively2.62m/s,3.69m/s,4.77m/s,theexperimentwascarriedoutindynamicliquidPbBiat550℃,uptoabout1500h.Accordingtotheresults,thesurfaceof316LhasbeencorrodedbadlyandtheelementsofNi,Cr,etc.werefoundtodissolvealot.WiththeincreaseoftheRFV,thefeatureof316Lsurfacechangedfromthesurfacewithmuchdeeperpitsandlooserstructurestotherelativeplanarone,andthethicknessoftheouteroxidelayerdecreasedgraduallywhilethatoftheinneroxidelayerdiminishedalittle,andthemicrohardnessoftheoutermostsubstratealsodeclinedincreasingly,inaddition,thedomainofthepartialsubstratewithitsmicrohardnessbeingaltereddeepenedfurther.Theseexperimentaldatawouldoffertheoreticalbasisandpracticalvaluestostudycorrosionconditionof316LsteelinliquidPbBiwithhigh-velocity.