Metallurgical Challenges in Joining Lightweight Dissimilar Materials Phil Prangnell & Joe Robson Acknowledgements Ying–Chun Chen, Lexi Panteli, Farid Haddadi, (Manchester) Stewart Williams, Supriyo Ganguly, Gonçalo Pardal, Sónia Meco (Cranfield) Hugh Shercliff, Aidan Reilly et al. (Cambridge– Dept. Engineering) Nick Wright, Mike Shergold (JLR), Tim Wilkes, Bruce Davies (MEL), A. Smith (Tarta), Tym Burman (Novelis)
School of Materials, University of Manchester, UK
LATEST2 – Priority Areas Energy efficient welding processes Joining dissimilar metals Composite to metal joining Integrated modelling - material interactions and joint performance Surface engineering for enhanced performance
Welding Multi-material Structures Al –Fe Phase diagram
Fusion techniques Resistance spot welding, GMAW, GTAW Laser etc.
Intermetallic reaction
Resistance spot welding Al to Steel
10 μm
IMC Layer
Qiu et al. Mater. Characterization 61 (2010)
Control of Interface Reaction Thin as possible < 200 nm
Ikeuchi, Yamamoto, Tikahashi, Aritoshi Trans JWRI 34 (2005)
(Direct drive rotational friction welding)
Target - Match Al to Al Joints (6111) Al â&#x20AC;&#x201C; Steel
3.5
3.5
3
3
2.5
2.5
Load (kN)
Load (kN)
Al to Al (6111)
2 1.5 1
1.5 1
0.5
0.5
0
0 0
1
2
3
Displacement (mm)
Full Pullout
4
Low Joint failure energy
2
0
1
2
3
Displacement (mm)
Interface cleavage
4
Focus
Energy Efficient Industrially viable - Spot Joining Methods for aluminium â&#x20AC;&#x201C; steel / magnesium
Current Spot Joining Methods for Al Resistance Spot Welding (RSW)
Energy/ Weld time
+ Fast - Electrode maintenance needed - High energy costs
~ 50 kJ Component surface
~ 0.3 sec Electrode
Self Pierce Riveting (SPR) + Good mechanical properties + Join through adhesive - High consumable costs - Hard metals?
Low < 0.5 sec
Alternative Spot Joining Methods Fusion: Rapid thermal Cycle Laser Conduction Spot Welding + Fast + low heat input + Excellent surface quality - Low efficiency
~ 40 kJ < 1sec Steel Al
Alternative Spot Joining Methods Solid state Friction Stir Spot Welding (FSSW) + Low energy - Keyhole - Slow ~ 2 - 4 kJ 2 â&#x20AC;&#x201C; 5 sec
Ultrasonic Spot Welding (USW) + Very low energy - Surface damage
< 1 kJ
< 0.5 sec
Laser Conduction Spot Welding Ring Clamp
Anvil
Uncoated Steel AA6111T4 - DC04 steel
Supriyo Ganguly, Gon莽alo Pardal, S贸nia Meco
Laser Conduction Spot Welding With â&#x20AC;&#x201C; Thermal management
Specific point energy vs. Intermetallic layer thickness (spot size = 13 mm, interaction time = 3 s)
IMC layer thickness 40
Intermetallic layer thickness [ď m]
35
Steel 30
Water cooled plate
25
Fe2Al5 20
FeAl3
Copper backing plate
15 10
Al
5 0 8.5
9.0
9.5
10.0
10.5
11.0
Specific point energy [kJ] Cu backing bar cooledvs. plateIntermetallic PowerWater density
layer thickness (spot size = 13 mm, interaction time = 3 s)
11.5
12.0
Laser Conduction Spot Welding With – Thermal management Specific point energy vs. Shear strength (spot size = 13 mm, interaction time = 3 s)
Lap Shear Strength
140
Water cooled plate
Cu Backing Bar Steel
Steel
Al
Al
100
80
60
Copper backing plate
Water cooled plate
40
20
IMC = 5 vsµm Temperature time - SP4
0 8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
Specific point energy [kJ]
IMC = 35 µm
1000
Cu backing bar Water cooled plate
Temperature
800 Temperature [°C]
Shear strength [MPa]
120
600 400 200 0 0
1
2
3 Time [s]
4
5
6
Laser Conduction Spot Welding With – Thermal management Specific point energy vs. Shear strength (spot size = 13 mm, interaction time = 3 s)
Lap Shear Strength
140
Cu Backing Bar
Water cooled plate
Shear strength [MPa]
120
Steel
Steel
Al
Al
100
80
60
Copper backing plate
Water cooled plate
40
20
0 8.5
9.0
9.5
10.0
10.5
11.0
Specific point energy [kJ] Cu backing bar Water cooled plate
11.5
12.0
IMC = 5 µm
IMC = 35 µm
Laser Conduction Spot Welding With â&#x20AC;&#x201C; Thermal management Specific point energy vs. Shear strength (spot size = 13 mm, interaction time = 3 s)
Relative Lap Shear Strength 140
Water cooled plate
Cu Backing Bar
Shear strength [MPa]
120
100
80
60
Copper backing plate
Water cooled plate
40
St
St
Al
Al
20
0 8.5
9.0
9.5
10.0
10.5
11.0
11.5
12.0
Specific point energy [kJ] Cu backing bar Water cooled plate
Solid State Welding Al-Steel FSSW
friction spot welded Al deck lid to the galvanized steel bolt retainer on the Mazda MX-5. [Mazda Motor Corporation]
FSSW Al-Steel Objective Produce successful joints in short weld times ~ 1 second In thin sheet ~ 1 mm thick
Friction Stir Spot Joining Methods 1. Standard Pin tool Pin displaces bottom sheet Mechanical locking /hook Exposure of fresh surface
Al Fe
2. Pinless tool Flow confined to soft top sheet â&#x20AC;&#x201C; abrades bottom? or is this pure diffusion bonding?
3. Stitch, or Sweep Pin abrades bottom sheet
4. Refil Currently not used with hard materials?
Standard 10 mm diameter tool
Standard Pin Tool
Al Fe
Uncoated Steel
Standard 10 mm diameter tool 2000 rpm, plunge depth -1.6 mm, 1s, plunge rate 50 mm/min, withdraw rate 50 mm/min
AA6111T4 - DC04 steel
WC tool
3
3
2
2
1
0
Failure load Fracture energy
2
4
6
8
1
Fracture energy, kN.mm
Failure load, kN
Standard Pin Tool
Al Fe
Extent of mechanical locking is limited in thin sheet
10
Dwell time, s
Max Failure load ~ 80% Al-Al
Failure Energy ~ 40% weld time 7 seconds!
Small Pullout Area
-> longer times expands to include area Under shoulder
Standard Pin Tool Interface temperature top
bottom 200 µm
Reaction Layer Thickness top
1sec
5 sec
9 sec IMC layer 4 µm
bottom
IMC layer 1 µm
2 µm
Pinless Tool
Flat tool or tool with features
e.g. Wiper tool
6111T4 - DC04 steel
Lap Shear Test Failure Loads 1 Second dwell time Failure load, kN
1.000 1.250 1.500 1.750 2.000 2.250 2.500 2.750 3.000
3.0 2.5 2.0
ď ą Max Failure load 80% Al-Al
1.5
Top sheet thinning
Failure energy
1.0 -0.8
~ 25% Al-Al
-0.7 2000
Plunging depth, mm
1 Sec Dwell time
1600
-0.6
1200 Rotation
speed, rpm
-0.5 800
Optimum Not fully bonded
Reaction layer too thick/ Top sheet thinning
Reaction Behaviour Dwell time 1 sec
2 sec
5 sec
Wiper Tool
500 nm
IMC Layer Thickness (nm)
IMC Layer Thickness (nm)
700
600
Wiper tool 5 sec.
500 400
Flat tool 5 sec.
300 200 100 0 0
1
2
3
4
5
Radial Distance From Center (mm)
Model: Courtesy of Aidan Reilly & H. Shercliff
FSSW Zinc Coated Steels
Hot Dipped Zinc (DX56-Z ) Pinless tool
5 µm
η(Zn-Fe)
Fe2Al5-xZnx
Zinc Coated Steels: Weld Envelope 6111-T4/DX54Z
(a)
Plunge depth of 0.2 mm
Aluminium Steel
Defects 1 second dwell time
(b)
Plunge depthShear of 0.4 mm Cracks Disc pull out
(c)
Defect free of 0.8 mm Plunge depth
FSW tool
Impossible to weld
Wiper tool (tool steel) Flat shoulder profile (WC tool with coating) BUT Plunge rate 10 mm/min - retraction rate 5 mm/min
Very difficult
Lap Shear Test Failure Loads Aluminium to Zinc coated steel 6111-T4/DX54Z Failure load, kN
Al
3.5
Fe
3.0 2.5 2.0 1.5 -0.6 -0.5 -0.4
Plunging depth, mm -0.3 -0.2 2000
1750
1500
1250
1000
750
1 Sec dwell time
Rotation speed, rpm
ď ą Max Failure load 90% Al-Al
Welding cycle
Failure energy 75% Al-Al But too slow!
Plunge
Withdraw 1 sec
plunge rate 10 mm/min - retraction rate 5 mm/min
Total weld time > 6 seconds
Effect of Zinc on flow Behaviour 6111-T4/DC04
Un-coated 1600 rpm,-0.1mm,1s
Al Steel
6111-T4/DX54Z
1600 rpm,-0.3mm,1s
1 sec, 1600 rpm
Stick condition 6111-T4/DX54Z
Zn Coated 800 rpm ,-0.5mm, 1s
Al Steel 1600 rpm ,-0.5mm, 1s
Slip condition
Weld Temperatures
Peak Interface Temperatures 500
Temperature (C)
Centre = 406 °C 400
Al-Zn eutectic 381 °C
r/2 = 395 °C
300 200 100
0 0
10
Time (sec.) 2000 rpm ,-0.5mm, 1s
20
30
Dispersion of Zn Coat Zinc detected
Al-Zn eutectic
“Friction brazing”?
IMC Reaction Layer Hot Dipped Zinc (DX56-Z ) Al 5 µm
η(Zn-Fe)
Fe2Al5-xZnx
Fe2Al5-xZnx
Fe
Al 200 nm
Fe2Al5-xZnx
Fe2Al5-xZnx ~ 80 nm Little change from Zn bath
Fe
50 nm
Abrasion Circle FSSW ABC-FSSW
Pin abrades bottom sheet
Abrasion Circleâ&#x20AC;? FSSW Tool steel shoulder
WC probes
Start End
Full 10 width mm 15 mm Pin trace area ~8 mm
Tool diameter 10 mm Probe diameter 5 mm
Abrasion Circleâ&#x20AC;? FSSW Travel speed 60mm/min Rotation rate 18.2s
300mm/min
3.64s
600mm/min
1.82s
5754H24 2 mm thick
800 rpm
Travel speed Rotation rate 1 mm 6111T4 to DC04 steel
1.82s
1.82s
1.1s
1.1s
0.73s
0.73s
0.55s
0.55s
Abrasion Circle” FSSW “Dwell Time” 1.8
1.1
“Dwell Time” 0.6 sec.
Failure Load
4
Failure Load (kN)
0.7
Failure Energy (kN.mm)
5
3.6
3 2 1 0 0
800 rpm
500
1000
1500
2000
Travel Speed (mm/min.)
60 mm/min 300 mm/min 2000 mm/min
10 9 8 7 6 5 4 3 2 1 0
3.6
1.8
1.1
0.7
0.6 sec.
Failure Energy
1 sec 0
500
1000
1500
2000
Travel Speed (mm/min.)
6111T4 to DC04 steel
Fe For 1 sec. Dwell Time Max Failure load 100% Al-Al Al
Failure energy ~100% Al-Al
Failure Comparison FSSW Pinless tool Optimised 1 Sec Dwell
Al-Steel
FSAW Circle Weld 1 Sec Dwell
Interface Layer 60mm/min
Al Fe
interface Deformed grains
Al
Fe Fe
200 nm
Fe parent grains
200 nm
USW Al to Steel Automotive Sheet
Al- Uncoated Steel 0
Load (kN) Load(kN)
6111 - DC04
2.4 kJ
10 um
IMC
Fracture Path
10 um
1
4.5 4.5 4 3.5 3.5 33 2.5 2.5 2 2 1.5 1.5 1 1 0.5 0.50 0
3
3.5
4
1.4 kN kN 1.4 1.9 kN kN 1.9
0
3 Seconds
0.5
Time (Sec) 1.5 2 2.5
1000
2000 3000 Energy (J)
10 um
4000
5000
Modelling Interfacial Reaction in Dissimilar Welds
Al -Steel 1 um
3 Seconds
Al
Al5Fe2 AlFe AlFe3
Fe
‘Simple’ Predictions of IMC Layer Thickness Static Isothermal Kinetic data Al - Steel AA6111- DC04
1 Hour
0.5 Sec
4 Hours
40
10 µm
0 Q = 117 KJ / mole
a
-1/2
k = 0.0397 m s
b
-2 -1/2
500 C
ln (k) m s
500 C
d (m)
30
20
-4 -6 -8
10 -10 Expt. Fit
0 0
1
2
3
4
5
6
1/2
t (hrs)
Parabolic growth law d =C1 exp (-Q/RT) t1/2
-12 1.0
Expt. Fit
1.2
1.4
1000 / T(K)
1.6
1.8
Application to FSSW
6111 - Formable Steel DC04
Predictions of IMC Layer Thickness Peak Temperature 500 C 450 C 400 C
500 C Peak Temperature
IMC Layer450 thickness very C sensitive to peak temperature 400 C
Application to FSSW Dwell time 1 sec
5 sec
2 sec
500 nm
Predicted Layer Thickness
Interface Temperature ď&#x201A;°C
500 500 480 480 460 460
1 sec. 2 sec. 3 sec.
440 440 420 420 400 400 380 380 360 360 340 340 320 300
-2
IMC Layer Thickness (nm)
Predicted Max. Interface Temp.
0 0
2 2
4 4
Radial Distance from Centre (mm)
Distance from Centre (mm)
6
6
200 180 160 140 120 100 80 60 40 20 0
Flat tool 3 sec.
Flat tool 1 sec.
0
1
2
3
4
5
Radial Distance From Center (mm)
6
Advanced Model - IMC Layer growth Application to Ultrasonic Spot Welding
Al-Al
Al – Mg AA6111 –AZ31
Mg
Mg
Mg-Mg Al-Mg 2 mm
Al
Mg
2 mm
Al- Mg IMC Layer growth Welding time
Mg
0.3 s 5µm
Al 10µm
0.5 s
5µm
10µm
M g IMC
Al
0.7 s
5µm
Mg
10µm Al12Mg17
1.0 s. 10µm
Al3Mg2 5µm
Al
Advanced Model - IMC Layer Growth Weld first forms at asperities
Mg 10Âľm
Al
Inter diffusion occurs
Al
Fe
Mg
Nucleation of of first IMC island
Interface diffusion controlled growth
Al12Mg17
Al3Mg2 Al
1D diffusion controlled growth
Advanced Model â&#x20AC;&#x201C; Example Predictions
micron
Temperature in weld cycle
Layer growth in weld cycle
Predicted vs measured layer thickness
Preventing IMC Reaction in Dissimilar Welds Process • Control of heat input • Avoid liquid phase
Metallurgical • Coatings - Separate weld from dissimilar joint - Diffusion Barrier coatings • Inhibitors
Thick Al- Pre Coating- Separate Weld from Dissimilar Joint E.G. Cold Spray Coatings in Al-Mg USWs
Joint failure energy
Al Coating
Mg
Cold Spray Al 50Âľm
Mg
Y-C Chen; Beijing Aeronatical
Thick Al- Pre Coating- Separate Weld from Dissimilar Joint E.G. Cold Spray Coatings in Al-Mg USWs
Effect on Joint failure energy
Mg
Al Coating
Cold Spray Al 50µm
Un-coated
Coated
Mg 10µm
10µm
10µm
Thin Barrier Coating Mn Coatings in Al-Mg USWs
2µm
Mg
PVD Mn coating ~ 0.9µm
Mg
John Nicholls - Cranfield
Failure Energy kN.mm
Effect on Joint failure energy
Al
USW – 0.4 Sec Mg Al
Thin Barrier Coating Mn Coatings in Al-Mg USWs
2µm
Mg
PVD Mn coating ~ 0.9µm
Failure Energy kN.mm
Effect on Joint failure energy
John Nicholls - Cranfield
USW – 0.4 Sec USW – 0.4 Sec
Thin Barrier Coating Mn Coatings in Al-Mg USWs
2µm
Mg
PVD Mn coating ~ 0.9µm
Failure Energy kN.mm
Effect on Joint failure energy
John Nicholls - Cranfield
USW – 0.4 Sec Uncoated
Coated Mg
Mg
Al
10µm
Al
Mg
10µm
Break up
Al 5 µm
Inhibition of IMC Reaction Al-Steel USWs Uncoated Steel 1.5 sec weld time
1 µm
3 sec weld time
1 µm
Fe2Al5-xZnx Passivated steel 1.5 sec weld time
1 µm
3 sec weld time
1 µm
Can You Fix Interfacial Reaction in Fusion Welding?? Laser welding
P. Peyre et al. / Materials Science and Engineering A 444 (2007) 327–338
RSW welding
10 µm
Ranfeng Qiua, et al. Mat. Sci Charact. 2010
Potential for Improving Passivation Layers on Zn Coated Steel for Fusion Welding to Aluminium e.g Out bursts occur by diffusion through passivation layer on grain boundaries.
Doping of Zn bath with rare earth mischmetal is known to inhibit outbursts and reaction between Fe and liquid Zn. e.g. Galfan coated Steel 0.03â&#x20AC;&#x201C;0.10 % Cerium + lanthanum
Summary The thickness of the intermeteallic reaction layer is a key issue in dissimilar metal welding even with solid state processes. => Poor joint failure energies The reaction layer thickness can be reliably predicted with kinetic models. Novel friction welding techniques can be used to successfully weld Al and dissimilar metal combinations with very high energy efficiency. Rapid fusion processes, with careful thermal management, are viable. There is potential to use pre-coatings and tailor galvanising on steel to inhibit reaction - allowing more flexible fusion welding.
LIGHT ALLOYS TOWARDS ENVIRNMENTALLY SUSTAINABLE TRANSPORT