1. Page 105/12/2015
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Effect of Time Delay Between Etching and Adhesive
Bonding on Lap-Shear Strength of Aluminum Alloys
Using Environmentally-Friendly P2 Etch
Matt Erich
Gokul Nair
Josh Barkhimer
Advisor: Prof. Kathy Chen
Sponsor: Steve Tunick

2. Page 2
Outlife is a critical factor when manufacturing processes use
etching and adhesive bonding
How long can etched aluminum be left out before
final bond strength is significantly reduced?
Outlife (Hours)
ShearStress(ksi)
?
2024-T3
6061-T6
7075-T6
Alloys
Alloy
Adhesive Bond

3. Page 3
Adhesive bonding is used as an alternative joining process in
multiple applications
Saves weight
Reduces stress concentrations
Avoids warping due to heat
Image Credit: http://www.sapagroup.com/upload/Sapa_Bonding_Aluminum.pdf
Tension
Spectrometry

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Creates an activated, porous oxide
film on the metal surface
Improves epoxy infiltration &
adhesion
May bind contaminants that
reduce final bond strength
Applying an etchant modifies the aluminum surface to improve
adhesive bond strength
"Surface Preparation Techniques for Adhesive Bonding", Second Edition, Wegman
and Van
Twisk, 2013 Chapter 2

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Sample
Preparation
Lap-Shear
Testing per
ASTM D1002
Analysis and
Statistics
Project consisted of sample preparation, lap-shear testing,
and statistical analysis of results

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Dry and
cure
Rinse etchant off and begin outlife
Degrease and scrub
Apply etchant
End outlife by applying adhesive
Single-lap shear specimens were prepared according to a
strict protocol (ASTM D1002)
7.75”
0.5”
.010” thick

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ASTM D1002 uses a tensile test setup
to find bond shear strength
Observed peeling & debonding
failure modes
1.00 in
0.50 in
The lap joints were pulled until the adhesive bond failed
Peeling Debonding

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Percent
Increase:
92.8%
The etching process increases the bond strength of aluminum
compared to non-etched

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Percent
Decrease:
15.3%
Expected
Shear
Stress:
3 ksi
ShearStress(ksi)
Outlife (Hours)
2024 FPL
Specimens of Al 2024 etched with FPL were tested as a
baseline for comparisons

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Percent
Decrease:
14.9%
Expected
Shear
Stress:
3 ksi
ShearStress(ksi)
Outlife (Hours)
2024 P2
Lap-shear bond strength decreases as the outlife time
increases
72

11. Page 11
Percent
Decrease:
21.0%
Expected
Shear
Stress:
3.1 ksi
ShearStress(ksi)
Outlife (Hours)
6061 P2
Al 6061 shows a similar trend of a decrease in bond strength
with an increase in outlife time
63

12. Page 12
Percent
Decrease:
20.2%
Expected
Shear
Stress:
3.5 ksi
ShearStress(ksi)
Outlife (Hours)
Al 7075 shows higher bond strengths compared to 2024 and
6061 alloys
63
7075 P2

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All three alloys experienced an overall decrease in bond
strength as outlife time was increased

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Summary
The etching process significantly improves bond strength
The P2 paste etchant has potential as a more environmentally-friendly
replacement for the current FPL paste
Increased outlife times generally result in lower shear strengths
ANOVA showed statistically significant changes past 1 hour outlife. Could not,
however, show significance for 2024 specimens due to wide scatter.

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Recommendations
Use larger sample sizes
Randomize samples
Store coupons in a desiccator during outlife times
Prepare samples in temperature and humidity-controlled
environment

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Summary
The etching process significantly improves bond strength
P2 etching reaches approximately same shear stresses as FPL
etching
Increased outlife times generally result in lower shear strengths
ANOVA showed statistically significant changes past 1 hour outlife. Could not,
however, show significance for 2024 specimens due to wide scatter.