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Collision Welding of Dissimilar Materials byVaporizing Foil Actuator: A BreakthroughTechnology for Dissimilar Materials JoiningGlenn S. Daehn (P.I. and presenter)Anupam Vivek (Co P.I.)The Ohio State UniversityProject ID:LM086This presentation does not containany proprietary, confidential, orotherwise restricted information

OverviewTimeline Start: October 2013 End: June 2016 Percent complete: 100%Budget Total project funding:DOE share: 568,499Barriers & Targets Barriers–Versatile methods forjoining dissimilar metals. Adhesives have low peel strength;we hope to do better Heat affected zones anddistortion are artifacts of fusionwelding we can do away with.Partners Honda: Materials selection andprocurement, industrialadaptation Alcoa: Materials procurement Tier 1 supplier and Equipmentbuilder being engaged now2

RelevanceObjectives To reduce vehicle weight by optimizing materialselection for various parts of the structure To incorporate metals with high strength-to-weightratios: high-strength steel, aluminum, and magnesium To enable dissimilar metal joining by Vaporizing FoilActuator Welding (VFAW) Current phase: To characterize 5 downselected material systemsand understand their failure mechanisms To develop a commercialization planUniqueness and Impacts Uniqueness: VFAW entails miniaturization of impact welding a typical industrial scale It can enable joining of dissimilar metals for creating multimaterial structures The 2nd phase of the project also aims to study corrosion mitigation strategies forsuch structures3

Approach: Basic Method of VFAWWhen energy is deposited at a very high rate, a thin conductor can be heated far aboveits energy of sublimation due to the constraint of inertial and magnetic forces. Whenthese forces let go, the conductor vaporizes and the stored energy is released as apressure pulse.4

Approach: Process DetailVivek, A., S R Hansen, and Glenn S Daehn. 2014. “High Strain RateMetalworking with Vaporizing Foil Actuator: Control of Flyer Velocity byVarying Input Energy and Foil Thickness.” The Review of ScientificInstruments 85 (7) (July): 075101. pubmed/25085167.5

Approach: Dissimilar WeldsCross sections and peel strengths of early welds:6

ApproachYear 1: Selection of materials and systems Goals: Industrially useful strong and corrosion resistant desired couples Honda, EWI, and Johnson Control Inc. assist in selection of 1mm thick sheet alloysand corrosion strategies. Pairs to be joined:Al-Fe, Fe-Mg, Mg-Al and Fe-I-Al, Mg-I-Fe When corrosion potentials 0.25 V different,intermediate layer may be needed.3-layer bonding is feasible based on preliminary work.Year 2: System joint testing and characterization Microscopy: optical microscopy, SEM, EDS Mechanical testing: lap shear, peel Corrosion testing: B-117 (with and without e-coating) Characterization of corrosion-tested samples: mechanical testing and microscopy7

ApproachYear 3 (extension): Further study of failure mechanism Goals: Strategy for mitigating corrosion based on understanding of corrosion andfailure mechanisms. Previous work indicates 4 factors which may accelerate corrosion. 9 cases are being corrosion-tested to help study the effects of the 4 factors FractographyScale up and commercial viability Ongoing interactions with Honda will keep work guided to utilitySmall efforts in: determining limits of vaporizing foil method with respect togeometries possible and length and area of foil that can be vaporized anddeveloping a design methodology. Work is underway to commercialize the technology through collaboration withequipment builder, Coldwater Machine Company, and automotive tier supplier,Magna International Inc.8

MilestonesPeriodTaskStatusYear 1Selection of 15 material combinationsCompletedScreening test of the 15 material combinationsCompletedDownselection to 5 material combinationsCompletedMicroscopy/microstructural analysisCompleted. Further work ongoingMechanical testingCompleted. Further work ongoingCorrosion testingCompleted. Further work ongoingMicroscopy of corrosion-tested samplesCompletedMechanical testing of corrosion-tested samples Retain 80% strengthCompleted. 80% goal achieved for5 out of 7 material systemsDeveloping techniques and fixtures for industryreadinessCompletedInvestigate corrosion and failure mechanisms bycorrosion and mechanical ar 2Year 39

Technical Accomplishments and Progress– Five out of seven material pairs retained 80% lap-shear strength through 30days of ASTM B117 salt-spray corrosion testing, with protective coating.From last year: AA6061-T4/DP780* 6061-T4/JAC270F* AA6061-T4/AM60BFrom this year: AA5052/JAC980* AA5052/JSC1500* AA6111-T4/JAC980* AA6111-T4/JSC1500* 80% strength retained––––Weld interfaces without continuous IMC layer were obtainedAA6061-T4 flyer up to 2 mm thick was welded to DP780 steelSemi-automated pedestal spot welder is built and operationalCommercialization of the technology is underway through collaborationwith Coldwater Machine Company (welding equipment maker) and MagnaInternational Inc. (automotive tier supplier).– Spot welding of Al/Fe was achieved at 2.5 kJ input energy ( 1/10 of RSW),thanks to a new high-efficiency pulse power supply and weldingconfiguration.10

2 mm thick Al flyer Thickest Al flyer successfully welded to steel(Impact speed 660 m/s)11

Al/Fe and Al/Mg jointsDP 780AA6061500 μmJAC270FAA6061500 μmAM60BAA6061500 μm12

Al/Fe and Al/Mg joints Corrosion and mechanical testing of Al/Fe and Al/Mg joints– 80% strength retained for both coated Al/Fe joints (lap-shear)13

Al/Fe joints of high-strength alloys Weld cross sections of four high-strength Al/Fe combinations– IMC-free regions were obtained at the interfaces of all fourcombinations14

Al/Fe joints of high-strength alloys Refinement and elongation of grains near interfaceFe:JSC980Al:AA6111-T415

Al/Fe corrosion testing Corrosion and mechanical testing– 80% strength retained for three of thecoated Al/Fe combinations (lap-shear)– Differences in open cell potentials was small( 60 mV) among base metalsMetalAA5052AA6111-T4JAC980JSC1500OCP (V SCE)-0.746-0.698-0.758-0.690* Strength of base Al**0.94 mm thick AA5052**1 mm thick AA6111-T4 Peak load of FSWAA5754/DP600 witha 2mm-thick Al sheet(Shen et al., 2015)Shen, Z., Y. Chen, M.Haghshenas, and a.P. Gerlich.2015. “Role of WeldingParameters on Interfacial Bondingin Dissimilar Steel/aluminumFriction Stir Welds.” EngineeringScience and Technology, anInternational Journal 18 (2): 105.

Corrosion of base AlSample which failed in Al in lap-shearUnderside ofcorroded AlProfiles of pit17

Corrosion mechanismCase1. As weldedGalvanicJettedStrain/couple materials thinningSchematicAl 2. Creviceremoved 3. Creviceremoved jet removed Fe4. Flattened 5. Overhangcut loose jetted materialsCrevice brush damage18

Corrosion mechanismCase6. Overhangw/ jetremovedGalvanicJettedStrain/couple materials thinningSchematicAlCrevice Fe7. Basematerials8. Base mat.w/ brushdamage9. Al-Al weld (not galvanic) jetted materials brush damage19

Pushing for industry readinessEngaging industry partnersSemi-automated pedestal spot welder 80 customer-discovery interviewsthrough I-Corps @ Ohio Collaboration withoHonda (fatigue testing)oColdwater (welding equipment)oMagna (component)Low-inductance capacitor bankCapacitor Control Pedestal spotbankunitwelder Short current rise time Spot weld at 2.5 kJ ( 1/10 of RSW)VFAW spot weld Materials: AA5052/JSC590 Input energy: 2.6 kJ Failure load: 6000 N20

Pushing for industry readinessPlans for robotic welderCapacitorbankRoboticarmWelderhead21

Answers to Reviewers’ CommentsCommentResponse“The need for a standoff gap In related work, we are devising new weldingappears to be problematic in geometries where the standoff gap is provided by aautomotive design”pre-formed target, leaving no open gap at the end.vs.“Collaborators haveprimarily provided opinionsand guidance, rather thanshared responsibility for theresearch.”Honda is becoming deeply engaged and initiatingstudies on fatigue resistance of welds. This must beunderstood prior to commercialization.“there was little interactionwith a supplier tocommercialize this process”We are engaging new partners to help commercializethe technology: a welding equipment manufacturer,Coldwater Machine Company, and an automotive tier 1supplier, Magna International Inc.22

CollaborationHonda America: Duane Detweiler, Tim Abke, Pete Edwards (Honda R&D andengineering)Role: Benchmarking of VFA spot welds against resistance spot welds.Guidance with material selection and procurement.Alcoa: Dan Bryant and Edmund Chu (Alcoa)Role: Material selection and procurement.Ohio State University, Fontana Corrosion Center: Prof. Rudy Buchheit andProf. Jen LockeRole: Will help with corrosion testing of coated and uncoated welds andunderstanding corrosion mechanisms at play23

Technical Summary/Future Work Vaporizing foil actuator welding (VFAW) produces robustdissimilar-metal welds with favorable microstructures 80% strength retention through corrosion testing wasachieved by protective coating for 5 out of 7 pairs tested Investigation on corrosion and failure mechanisms is inprogress and will continue We continue to push for industry readiness.– Semi-automated pedestal welder is built and operational– Development of welding done in industrially relevant geometries continues– Using a faster capacitor bank, spot welding was achieved using 2.5 kJ (about10% of energy required for Resistance spot welding)– Work is underway to commercialize the technology through collaboration withequipment builder, Coldwater Machine Company, and automotive tiersupplier, Magna International Inc.24