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Hydro Aluminium
Light Metal Surface Science Annual Conference
NTNU Trondheim, 22-23 January 2004
Tomas Luksepp and Håkon Leth-Olsen
Durable Adhesive Bonded Joints

Introduction
The person who deals with lap shear testing of
adhesive bonded joints has a problem with the
environment!
The human environment!
Date: 2004-01-13 • Page: 2 • Hydro Aluminium

Introduction
Maybe little of a general view
Suspect tests performed by suspect
individuals with suspect results!
Why?
The person can never give the answer YES, IT WORKS! without a but.
To many parameters affects the results.
No “buts” in industrial use.
Date: 2004-01-13 • Page: 3 • Hydro Aluminium

Outline
Test methods to establish durability confidence
Lap shear testing, 5 years outdoor results
Testing with road mud or salt solutions
Environmental fatigue testing
Summary / conclusions
Date: 2004-01-13 • Page: 4 • Hydro Aluminium

Accelerated lap shear testing
A ranking test, only qualitative
Only a limited number of parameter can be compared in
each matrix
Rather complicated, experience required, expensive
The ultimate lap shear ageing test does not exist
Nevertheless, it simulates the real joint
Date: 2004-01-13 • Page: 5 • Hydro Aluminium

Hydro, lap shear testing
SWAAT, (Sea Water Artificial Acidified Test)
– 49°C, cyclic, 30 min spray, pH 2.8-3.0, 90 min, 98% RH
Outdoor, salt spray once a week, 45º south side
Cassette underneath trailer, natural mud
– Gothenburg – Raufoss, Norway on a daily base
Trailer + Outdoor, on ground, no salt, no sun
Initiation, 16 % HCl, 10 min
Orientation
Outdoor Trailer
Date: 2004-01-13 • Page: 6 • Hydro Aluminium

Failure surfaces, after 1 year on trailer
Example
Extrusion, 6060.35
Adhesive, Betamate XW1044-3
Degreased Degreased + HCl Etched + HCl
The Near Surface Active Region from thermo- mechanical
processing has to be removed
5 % 30 % 1 %
Date: 2004-01-13 • Page: 7 • Hydro Aluminium

Amount of visual corrosion and/or delamination in percent of
area for each lap shear specimen
SWAAT Outdoor HCl + Outdoor Outdoor Outdoor Trailer HCl + Trailer HCl + Trailer +
Surface 6 weeks 1 year 1 year 2,5 year 5 year 1 year 1 year Outdoor*,
Adhesive 1 year + 1 year
DEG XW1044-3 0 0 5 25 50 0 0 0 0 0 0 0 0 0 0 0 0 2 10 10 5 20 25 40 50 0 0 5 5 5 30 30 30 30 30 50 50 60 60 70
DEG B 1494 0 0 0 0 10 0 0 0 10 10 0 0 0 0 10 0 0 0 0 20 0 1 10 10 30 0 0 0 5 5 30 30 30 30 30 50 70 80 85 95
DEG XD4600 70 80 80 90 100 0 0 5 5 5 1 1 5 5 10 0 0 0 10 20 10 20 20 40 40 15 15 15 15 15 50 75 85 100 100
DEG WC2310 0 0 2 2 2 15 15 15 20 20 10 10 20 30 40 0 5 5 5 5 50 50 50 50 50 40 90 95 95 95
ETCH XW1044-3 0 0 0 2 25 0 0 0 0 0 0 0 0 0 2 0 0 0 0 1 0 0 0 0 1 0 0 0 1 1 2 2 5 10 20
ETCH B 1494 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 10 0 0 0 1 1 0 0 0 0 0 0 0 0 1 1 0 1 2 5 5
ETCH XD4600 0 0 1 2 30 0 0 0 0 0 0 0 0 0 0 0 0 0 5 5 0 0 0 1 5 0 0 0 0 0 0 0 5 10 25 0 0 1 1 2
ETCH WC2310 80 100 100 100 100 0 0 0 0 0 0 0 0 0 0 30? 30? 30? 0 0 0 0 0 0 0 0 0 0 1 2 5 10 10
ETCH XB5315 0 1 1 2 2 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ETCH AV119 0 0 0 10 20 0 0 0 0 0 0 0 0 0 0 0 0 0 5 10 10 10 15 30 50
ETCH DP490 50 50 85 100 100 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1 * no salt, no sun
ETCH 3M 5047 0 0 0 0 0 0 0 0 0 0 1 1 1 1 1
TiZr XW1044-3 0 0 0 5 10 0 0 0 0 0 0 0 0 0 2 0 0 0 5 5 0 0 0 5 30 0 0 0 1 1 0 0 1 1 1 10 15 20 25 60
TiZr B 1494 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 10 10 20 25 40 0 0 0 0 1 1 1 1 1 10 10 20 20 30 75
TiZr XD4600 5 30 30 30 50 0 0 0 0 0 0 0 0 0 0 0 0 0 2 2 0 0 0 0 0 0 0 10 10 10 15 25 40 40 50
TiZr WC2310 0 0 0 0 0 1 1 2 2 2 0 0 2 10 10
SAA XW1044-3 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
SAA B 1494 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
SAA XD4600 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 10 0 0 0 0 10 0 0 0 0 0 0 0 0 0 0
SAA XB5315 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ROCA XD4600 1 1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
ROCA WC2310 5 5 15 15 25 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
PY XD4600 90 90 90 90 90 0 10 30 30 50 85 90 95 95 100 60 80 90 100 100 10 25 25 25 40 70 80 80 90 100 95 100 100 100 100
PY WC2310 0 0 0 0 2 2 2 2 2 5 5 5 10 15 15 5 5 5 5 5 50 60 60 60 70 50 60 100 100 100
2-k adhesive 1 - 5 % 5 - 15 % 15 - 100 %
Date: 2004-01-13 • Page: 8 • Hydro Aluminium

Main ageing notes
Outdoor, with salt spray
1 year, not selective enough
Initiated corrosion may not propagate
Trailer
At least 2 times as corrosive than accelerated outdoor.
Trailer + outdoor storage
Condition for corrosion propagation is present
SWAAT
Proper ranking?
Mainly a corrosion failure mechanism in service
Adhesives, relatively small differences
Surfaces, large differences
Detailed test results will be available via the Automotive Manual, European Aluminium Association in
the appendix report from working group GTP 4, General Test Procedures- Bond durability
Date: 2004-01-13 • Page: 9 • Hydro Aluminium

Road mud effects
Why is the trailer test worse?
The mud provided chlorides and extended time of wetness.
Reduce dilution/ washing effects.
Significant acidification. Dependant on salt composition.
Date: 2004-01-13 • Page: 10 • Hydro Aluminium

Mud weight vs. Relative humidity
Normalised weight
1,1
1
Mud incl. AlCl3 Mud 5x'Maritime'
Visually wet
0,9
0,8
0,7
0,6
0,5
0 10 20 30 40 50 60 70 80 90 100
Relative humidity (%)
’Maritime’ salt solution
from Dutch roads
Species
Concentration (g/l)
NaCl 22,6
MgCl 2 x 6H 2 O 7,8
Na 2 SO 4 4,0
CaCl 2 1,4
KCl 1,0
MgSO 4 x 7H 2 O 0,05
Ca(NO 3 ) 2 0,04
NH 4 NO 3 0,04
The mud is made of sea sand, kaolin and salt solution
The point of deliquescence for NaCl at RT is ~76 %, MgCl 2
and CaCl 2
~30 %
Date: 2004-01-13 • Page: 11 • Hydro Aluminium

Composition and pH of the salt solutions used
to produce the five muds.
Species Mud 1
Neutral
Mud 2
Acid
Mud 3
Maritime
Mud 4
Acid Mari.
Mud 5
Trailer
Water (g) 300 300 300 300 300
NaCl 50 47.5 33.9 33.9 39.43
AlCl 3
x 6H 2
O - 2.5 - Added till pH 0.46
4
MgCl 2
x 6H 2
O - - 11.7 11.7 1.32
CaCl 2
- - 2.1 2.1 5.91
Na 2
SO 4
- - 6.0 6.0 -
KCl - - 1.5 1.5 1.08
Mg 2
SO 4
x 7H 2
O - - 0.075 0.075 -
Ca(NO 3
) 2
- - 0.06 0.06 -
NH 4
NO 3
- - 0.04 0.04 -
FeCl 2
x 4H 2
O - - - - 0.25
pH 7.1 3.2 5.5 4.0 4.2
Date: 2004-01-13 • Page: 12 • Hydro Aluminium

pH values measured for the salt solutions and
the muds
Mud/solution no. pH in salt solution pH in mud slurry
1 7.1 3.8
2 3.2 3.1
3 5.5 3.9
4 4.0 3.6
5 4.2 3.7
Technical difficult to conduct pH measurement underneath a ‘dry’ mud film.
Clean sand might be washed in HCl
Kaolin affects pH
Date: 2004-01-13 • Page: 13 • Hydro Aluminium

pH for salt layers from solutions 3, 4 and 5 at
two RH levels
Mud/Solution no. 60 % RH 75 % RH In solution
Solution 3 4.7 5.2 5.5
Solution 4 2.6 4.2 4.0
Solution 5 2.9 3.7 4.2
Concentration and pH changes with relative humidity
Qualitative measurements
At 60 % RH the salt layer on the electrode appeared solid,
whereas at 75 % RH it appeared liquid.
Date: 2004-01-13 • Page: 14 • Hydro Aluminium

Test conditions
Test plates were coated with 1-2 mm mud and placed horizontal
in a 40 o C humidity cabinet for 4 weeks
48 hours humidity cycle:
24 hours at 85% RH and
24 hours at 50% RH
Pitted surfaces of etched AA6060
Date: 2004-01-13 • Page: 15 • Hydro Aluminium

Tested substrates
Designation Supplier Alloy Surface treatment
6060 etched Hydro Aluminium AA6060 NaOH etched (5 µm)
6060 anodised Hydro Aluminium AA6060 Etched and H 2
SO 4
anodised (4-7 µm)
6016 etched Pechiney AA6016 NaOH etched (5 µm)
6016 Ti-Zr cc Pechiney AA6016 Ti-Zr based CC (Gardobond X4591)
5754 etched Pechiney AA5754 NaOH etched (5 µm)
5754 Ti-Zr cc Pechiney AA5754 Ti-Zr based CC (Gardobond X4591)
5018 etched Corus AA5018 NaOH etched (5 µm)
5018 Ti cc Corus AA5018 Ti based CC (Alodine 2010)
Date: 2004-01-13 • Page: 16 • Hydro Aluminium

Average weight loss for the different alloys and pretreatments
after four weeks exposure with different muds in the humidity
cabinet.
Mud 1 Mud 2 Mud 3 Mud 4 Mud 5
20
18
16
14
12
10
8
6
4
2
0
Weightloss [mg/ (cm 2 year)]
6060 / etched
6060 / anodised
6016 / etched
6016 /Ti+Zr cc
5754/ etched
5754 /Ti+Zr cc
5018 / etched
5018 / Ti cc
Date: 2004-01-13 • Page: 17 • Hydro Aluminium

Average pit density after four weeks exposure
Mud 1 Mud 2 Mud 3 Mud 4 Mud 5
90
80
70
60
50
40
30
20
Pit density [cm -2 ]
0
10
6060 / etched
6060 / anodised
6016 / etched
6016 / Ti+Zr cc
5754/ etched
5754 / Ti+Zr cc
5018 / etched
5018 / Ti cc
Date: 2004-01-13 • Page: 18 • Hydro Aluminium

Average pit depth after four weeks exposure.
Mud 1 Mud 2 Mud 3 Mud 4 Mud 5
200
150
100
50
Pit depth [m]
0
6060 / etched
6060 / anodised
6016 / etched
6016 / Ti+Zr cc
5754/ etched
5754 / Ti+Zr cc
5018 / etched
5018 / Ti cc
Date: 2004-01-13 • Page: 19 • Hydro Aluminium

Mud test, summary
The composition of a road mud affects the
corrosion behaviour.
The effect has to be understood to better
correlate lab tests with in-service behaviour.
No one wants mud as a parameter in standardised
tests.
Date: 2004-01-13 • Page: 20 • Hydro Aluminium

Requirements on a corrosion screening test
Simple qualitative screening before advance testing
Ranking ability
Fast and simple
A large number of specimen permutations
A few graded assessment scale would be enough
Date: 2004-01-13 • Page: 21 • Hydro Aluminium

Salt solution corrosion test
Small specimens partly coated with adhesive
Horisontal exposure with almost saturated salt solutions
Duration: 3 months
Temperature: 40°C
Humidity: 12 hours cycle;
6 h at 85% RH, 6 h at 50% RH.
Evaluation of corrosion on the open surface and under cutting the
adhesive (delamination).
Date: 2004-01-13 • Page: 22 • Hydro Aluminium

Salt solutions
Salt no.
1
2
3
4
5
6
7
Salt solutions
Pure NaCl
95% (wt) NaCl + 5% AlCl 3
“Maritime solution”
“Maritime solution” + AlCl 3 to pH 4
“Mud 5 solution” (artificial trailer)
Pure CaCl2
Pure MgCl2
Measured pH
5.4
2.3
4.5
3.8
2.5
3.6
4.9
Almost saturated solutions when applied
pH measurement on diluted solutions 1:9
Date: 2004-01-13 • Page: 23 • Hydro Aluminium

Example of screening of systems
12 weeks exposure with salt 4, “Maritime solution” + AlCl 3 to pH 4
4
Rank
Adhesive
delamination
Corrosion on
bare surface
Ranking
3
2
1
Delamination
Corrosion
0
1
2
0%
0-5%
5-15%
No corrosion
No surface
corrosion, some
pitting corrosion
Surface
corrosion, no or
very limited
pitting
0
1 2 3 4 5 6 7 8
Material No.
Systems responds differently and ranking is obtained.
3
4
15-30%
>30%
Surface and
pitting corrosion
Surface
corrosion and
extensive pitting
and general
corrosion (>
30% of surface)
Date: 2004-01-13 • Page: 24 • Hydro Aluminium

Tested materials
Adhesive
Heat curing epoxy, XD 4600, Dow
Surface
Hot AC (alternated current) anodised 3105 (Material 2)
– Iron rich metal, reactive surface layer converted?
5754 passivated (Material 4)
– ?
Date: 2004-01-13 • Page: 25 • Hydro Aluminium

3105 H44 Hot AC SAA, 3 months exposure
2 Acid NaCl 5 Art. trailer 6 CaCl 2 4 Acid Maritim
pH = 2.3 pH = 2.5 pH = 3.6 pH = 3.8
3 Maritim 7 MgCl 2 1 NaCl
pH = 4.5 pH = 4.9 pH = 5.4
Blisters from
cut edge
SWAAT and
service
performance?
Date: 2004-01-13 • Page: 26 • Hydro Aluminium

5754 passivated, 3 months exposure
2 Acid NaCl 5 Art. trailer 6 CaCl 2 4 Acid Maritim
pH = 2.3 pH = 2.5 pH = 3.6 pH = 3.8
Salt 3 vs 1 in a
accelerated
lap shear test?
3 Maritim 7 MgCl 2 1 NaCl
pH = 4.5 pH = 4.9 pH = 5.4
Date: 2004-01-13 • Page: 27 • Hydro Aluminium

Screening of salt solutions
12 weeks exposure of 3105 hot AC (2) and 5000 (4)
Shorter test times could be enough
4
4
Corrosion Ranking
3
2
1
Delamination ranking
3
Surface 2 2
Surface 4
1
Surface 2
Surface 4
0
1 2 3 4 5 6 7
0
1 2 3 4 5 6 7
Salt No.
Salt No.
Date: 2004-01-13 • Page: 28 • Hydro Aluminium

Summary, salt solution tests
Acidification is a most important acceleration factor.
Relevant test conditions will vary with market place.
A very simple and fast test with ranking ability for both
initiation and propagation has been demonstrated, suitable?
”Massive screening could be made relatively cheap”
– Substrate initiation and undercutting propagation
– Screening of environmental conditions
– Screening of many systems at fixed relevant conditions
Date: 2004-01-13 • Page: 29 • Hydro Aluminium

Cyclic stress testing with environmental load,
principles
Reinforced Double Cantilever Beam, RDCB
Crack-
Length
Reinforcements bonded on,
prevents yielding
With constant
deformation
Crack growth rate
Log da/dN (mm/cycle)
"Wet"
"Dry"
Gc, static
Adhesive
fracture
energy
Gth
Log Gmax
Loadcycles
Load measures => crack length
Maximum value of strain energy
release rate during a fatigue cycle
Date: 2004-01-13 • Page: 30 • Hydro Aluminium

Baseline testing, ambient conditions
1,E-02
Dry testing of adhesive XD4600
da/dN [mm/cycle]
1,E-03
1,E-04
1,E-05
1,E-06
1,E-07
Ti/Zr, x4707
Etch ’Short’
Degreased
X4707 - XD4600
Etched HRE- XD4600
Degreased - XD4600
Etched RDK ’Long’ - XD4600
10,00 100,00 1 000,00
G max [J/m 2 ]
The surface pretreatment affects fatigue resistance
Date: 2004-01-13 • Page: 31 • Hydro Aluminium

Failure modes
Start of test, End of test
Deagreased
Oxide failure
Ti/Zr, x4707
Initial crack, PTFE shims
Coating failure
Date: 2004-01-13 • Page: 32 • Hydro Aluminium

Failure modes (2)
Interfacial failure
’Short’
etch
’Long’
etch
Cohesive failure
Date: 2004-01-13 • Page: 33 • Hydro Aluminium

TEM, Altered layer on etch (1)
At microtoming the
first altered layer
exhibit a waved crack,
indicating changed
mechanical properties
Long etching time
and no desmutting
At both dry and wet
fatigue testing, crack
Propagation occurs in
the bulk of the adhesive
Mineral fillers are
magnitudes larger than
the thixotropy agent
(fused silica)
Aluminium
Adhesive
Gunnar Pettersson, Sintef
5 µm
Date: 2004-01-13 • Page: 34 • Hydro Aluminium

TEM, Altered layer on etch (2)
Long etching time and no desmutting
BULK
Atom %
C O Mg Al Si
75 12 0 0 13
A2
A1
Aluminium
Gunnar Pettersson, Sintef
Adhesive
XD4600
5 µm
92 6 0 1 1
42 15 17 18 8
Altered layer
1. Adhesive and oxides
mixed as a micro
composite
2. Polymer rich layer,
with less thixotropy
agent
Cohesive fatigue failure
Date: 2004-01-13 • Page: 35 • Hydro Aluminium

TEM, Altered layer on etch (3)
’Short’
etch
Aluminium
At the interface
10 m into the adhesive
Interfacial
fatigue
failure
200 nm 200 nm
Altered layer
A1, ’composite’
A2, ’polymer’
’Long’ etch time
4 m, full coating
Distinct, Si free layer
’Short’ etch time
1 m, partially ’nothing’
Reduced amount of Si particles
Date: 2004-01-13 • Page: 36 • Hydro Aluminium

Summary, environmental fatigue testing
A good tool for testing bond system durability performance with
respect to weak boundary layers and wet adhesion
(Supported by surface characterisation techniques)
Quantitative measurements
Data for life predictions
Not suitable for corrosive environments
Fatigue is generally not an issue
for a bonded automotive designs!
Date: 2004-01-13 • Page: 37 • Hydro Aluminium

The toolbox for confident durability testing
Current screening, lap shear tests
Corrosion
Wet adhesion
Relevant configuration
Many different tests
Field correlation ??
Verification
New screening tests, (mud) or salt solution tests?
Corrosion propagation
Fast and simple
Corrosion initiation
Advanced testing, environmental fatigue, DCB specimens
Weak boundary layers
Quantitative test
Wet adhesion
Date: 2004-01-13 • Page: 38 • Hydro Aluminium

Conclusion
Durable bonded joints requires good
Wet adhesion
Corrosion resistance
Tools for durability assessments are available.
Durability confidence for bonded joints will be achieved.
Date: 2004-01-13 • Page: 39 • Hydro Aluminium