Materials & Advanced Manufacturing (M&AM) Evaluation of - PowerPoint PPT Presentation

Materials & Advanced Manufacturing (M&AM) Evaluation of Candidate Methods for Welding Steel to Other Structural Lightweight Metals Jerry E. Gould , Mike Eff, and Kate Namola Resistance and Solid State Welding EWI ph: 614-688-5121 e-mail: jgould@ewi.org 8/10/2018

Dissimilar Materials Joining Needs Materials & Advanced Manufacturing (M&AM) for Various Industries

Key Dissimilar Materials Joining Materials & Advanced Manufacturing (M&AM) Needs for Military Applications • Aluminum to steel assembly • Titanium to steel/Ni-base alloy – Lightweight composite gears assembly – Transition joints for ship – Lightweight torsion shafts construction – Gas turbine engine shafts – Lightweight blast protection – Sub-system bracket assemblies Page 3

Materials & Advanced Issues with Joining Al to Steel Manufacturing (M&AM) Large difference in melting points • Formation of low melting temperature • constituents • Difference in crystal structure – Al is FCC, Fe is BCC • Multiple intermetallic phases

Key Factors in Friction Processing for Materials & Advanced Manufacturing (M&AM) Aluminum to Steel Joints Metallurgical factors • – Reduced peak temperatures – Reduced times at temperature Geometric factors • – Designed interfacial topography Temperature excursions in friction welds • – Yield strength as a function of temperature – Applied contact pressures – Implicit peak temperature variations for different aluminum alloys • Design of the thermal cycle – Example for inertia welding

Friction Welding Aluminum Materials & Advanced Manufacturing (M&AM) to Steel Process characteristics • – Inertia and direct-drive friction welding variants – Low surface velocities – Short heating times – Forging only in the aluminum Macrosection of an aluminum to steel inertia friction weld Temperature profile of the interface of dissimilar FWed joint 450 3000 Steel 400 Aluminium 2500 350 2000 Temperature (C) 300 1500 RPM 250 1000 200 500 150 0 100 0 100 200 300 400 500 -500 50 Time (ms) 0 Deceleration profile for an inertia weld between 0 5 10 15 20 25 30 35 aluminum and steel Time (s) Typical thermal cycle for an Al-to-steel inertia weld

Example of Designing an Aluminum to Materials & Advanced Manufacturing (M&AM) Steel Inertia Welding Process Relationship between part size and  process parameters Scaling is critical to properly size the  welding hardware for large cross sections

Joint Morphology vs Total Cycle Materials & Advanced Manufacturing (M&AM) Time 320 ms Average Tensile = 318 MPa 280 ms Average Tensile = 306 MPa

Application of Linear Friction Welding to Materials & Advanced Manufacturing (M&AM) Aluminum – Steel Joints • Dedicated electric servo- drive LFW machine • Working interface ~12-mm x 12-mm • Targeting pressures and heating times to match IFW results • Effective heating times <200-ms • Observed aluminum material loss ~8-mm

Aluminum – Steel LFW Process Materials & Advanced Manufacturing (M&AM) Observations • Oscillation of the steel component • Use of square joint faces • Burn-off on aluminum side only • Material loss ~8- mm

Aluminum – Steel LFW Metallurgical and Materials & Advanced Manufacturing (M&AM) Mechanical Observations • High contact pressures used for joining • Implicit surface topography • Enhanced plasticized material at interface • Lack of observable intermetallics • Joint strengths ~300- MPa

Friction Stir Welding of Aluminum Materials & Advanced Manufacturing (M&AM) to Steel FSW processing for continuous • joints • Al6061 to 1018 steel • Specially designed tool – Zero tilt – Large diameter pin – Flutes and threads • Materials ~3-mm thick • Tool offset to the aluminum side • Tool shoulder 0.25-mm above steel surface • Scarfing of the steel interface • Processing speeds ~8.5-mm/s

Aluminum to FSW Microstructures Materials & Advanced Manufacturing (M&AM) and Properties • Transverse tensile testing shows failures in Al HAZ • Joint strengths ~200-MPa Bend performance along • joint • Macrostructures show: – Scarfing of the steel surface – Resultant texture – Flow of Al across steel surface • Residual intermetallics along bond line

Challenges for Titanium to Steel Materials & Advanced Manufacturing (M&AM) Joining • Eutectic formation – Ti-Fe eutectic temperature ~1073 o C • ~500 o C melting point suppression – Ti-Ni eutectic temperature ~972 o C • ~600 o C melting point suppression – Susceptibility to solidification and liquation cracking • Intermetallics – Ti-Fe and Ti-Ni intermetallic compounds – σ -phase formation – Bond line embrittlement • Carbides and nitrides – Titanium a strong carbide/nitride former

Key Factors for Joining Titanium Materials & Advanced Manufacturing (M&AM) Alloys to Steels • Use of Interlayers for Joining Titanium • Explosion bonding Alloys to Steels – Tantalum, Monel, and Copper all used as interlayers • Functionality of interlayers – Ductile components to absorb – Separation of the Ti and steel deformation during processing substrates – Bondability to the substrates • Arc welding using vanadium interlayers – Joint strengths up to 400-Mpa Diffusion bonding using nickel • interlayers – Joint strengths up to 260-MPa – Failure along a Ni-Ti intermetallic layer • Friction welding – Use of copper interlayers – Joint strengths up to 375-MPa

Application or Resistance Mash Seam Welding for Materials & Advanced Manufacturing (M&AM) Titanium Alloy to Steel Joining • Nominal butt joints • Defined small overlap between workpieces Application of resistance seam welding • • Forging of components together • Solid state joining • Defined levels of uniaxial strain • Potential for interfacial forging – Defined material interfaces – Separation of base materials – Series solid state joints 3 • Materials for study Bond Line Strain (Epsilon) – 3.5-mm CP Ti hot rolled sheet 0.5 T 2 1.0 T – 3-mm 304 SS hot rolled sheet 1.5 T 2.0 T • Beveled edges on the SS sheets 1 2.5 T – 65- μ m Nb strip (interlayer) 0 • Continuous seams following welding 0.8 1 1.2 1.4 1.6 1.8 2 2.2 Relative Joint Thickness (Delta)

Visual and Optical Assessments of Materials & Advanced Manufacturing (M&AM) the Resulting Joints • Optical observations of resulting joints – Welding to within a few 10’s of millimeters to the part edge – Smooth profiles on both the stainless steel and titanium – Ti seen to fill the bevel on the stainless steel – Residual Nb sheet seen to extend to both free Top Surface of an RMSeW made between 304-SS and Ti Sheet. edges of the joint Optical microscopy observations • – Bonding to within a few hundred microns of the joint free edges – Bi-axial deformation of the titanium sheet – Continuity of the Nb foil across the bond width Cross Section of the RMSeW between 304-SS and Ti

Interlayer Behavior in the Resulting Materials & Advanced Manufacturing (M&AM) Joints • Indications of bonding to within a few microns of the bond line Details of the bond line edge for edge a best practice Ti to SS RMSeW • Continuity of the Nb interlayer to the bond line edge • Resulting interlayer ~60- μ m wide • Minimal diffusion of species across the interlayer • Solid state character of the bond Microstructural and chemical variations evident on both sides of the across the bond line of a Ti to SS interlayer RMSeW with an interlayer • Joint strengths 200-MPa to 300- MPa

Microstructural Behavior in Areas Materials & Advanced Manufacturing (M&AM) of Foil Rupture • Some samples showed discontinuities near the Details of the bond line edge for bond edge a best practice Ti to SS RMSeW • Discontinuities appeared to be small ruptures in the Nb foils • Rupture resulted in localized constitutional melting • Melt zones grew into both Microstructural and chemical variations the Ti and SS across the bond line of a Ti to SS RMSeW • Composition of this zone with an interlayer suggests a Ti-Fe eutectic

Upset Welding Titanium Alloys to Materials & Advanced Manufacturing (M&AM) Steels • Resistance heating combined with axial forging • Rapid thermal cycling • Use of refractory metal interlayers • Resistance heating to provide softening and plasticity • Development of high faying surface strains • Simple (uni- and bi-axial) strain paths

UW Titanium Alloys to Steels – Process Materials & Advanced Manufacturing (M&AM) Response and Macrostructures Constant voltage power Preferential forging of the titanium • • • Two second heating time (2 – 1-s pulses) • Observable upset on the SS • Upslope employed for providing good initial • Two stage deformation behavior contact – Initial forging of the Ti-alloy Secondary forging of the SS – • Current variations related to changes in workpiece resistance