PPRD
01-003
Issue
1d
Date 24th Nov 2015
IAEG International Aerospace Environment Group
Process Performance Requirement Document (PPRD)
Chromate-free Chemical Conversion Coating of Aluminum Alloys
© 2015 IAEGTM
The International Aerospace Environmental Group™ ("IAEG™") is the owner of this material. This material may not be
used for any purpose other than that for which it is provided without the express written consent of IAEG™. IAEG™
will accept no liability either directly or indirectly for damages from any use of this material including without
limitation any indirect, incidental, special and consequential damages, loss of data, income, profit or goodwill, loss of
or damage to property or claims of third parties. IAEG™ reserves the right to add to, change or delete its content or
any part thereof without notice.
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© 2015 IAEGTM
PPRD
01-003
Issue
1d
Date 24th Nov 2015
1. INTRODUCTION
1.1. PURPOSE
This Performance Requirement Document is intended to be used by the IAEG members to identify
and evaluate chromate-free alternatives to Chemical Conversion Coating of aluminum alloys used in
aerospace applications. Performance requirements for other technologies are in a case by case
basis, contact IAEG for more information.
1.2. SCOPE
The present document is providing requirements to obtain an entirely chromate-free process for
chemical conversion coating. Any pre- or post-treatment should be clearly specified and shall be
chrome free.
This document makes reference to ASTM B117, ISO 9227 and ISO 21207 as suitable and
equivalent methods for demonstrating Potential alternative Chemical Conversion Coating processes.
1.3. DISCLAIMER
This specification is being distributed strictly for the purpose of evaluation and identification of
replacements in the frame of the IAEG WG2 Zero project {Oct 2015 - }.
This specification and all technical data, requirements and other information contained herein, is
proprietary to and the intellectual property of IAEG. No reproduction, copy or use thereof may be made
without the express written consent of IAEG, except to those with a need-to-know for the purpose noted
above.
Use of this specification and/or the technical data or requirements contained herein without the express
written approval of IAEG is at user's risk and IAEG expressly disclaims responsibility for such use and
the situations that may result therefrom.
IAEG reserves the right to modify, at any time, this specification and/or the technical data and
requirements contained herein.
IAEG makes no warranty, express or implied, that utilization of the technology or products disclosed
herein will not infringe any industrial or intellectual property rights of third parties.
2. APPLICABILITY
The PPRD 01-003 is intended to be used to evaluate the performance of Chemical Conversion
Products by either continuous exposure to neutral salt fog or by exposure to a mixture of neutral salt
for and corrosive gases.
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© 2015 IAEGTM
PPRD
01-003
Issue
1d
Date 24th Nov 2015
3. GENERAL REQUIREMENTS
3.1. ENVIRONMENTAL COMPLIANCE
The alternative process shall utilise the principles of green chemistry.
3.1.1. Additional notes about green chemistry based on 12 principles:
3.1.1.1.
Prevention - It is better to prevent waste than to treat or clean up waste after it has
been created.
3.1.1.2.
Atom Economy - Synthetic methods should be designed to maximize the
incorporation of all materials used in the process into the final product.
3.1.1.3.
Less Hazardous Chemical Syntheses - Wherever practicable, synthetic methods
should be designed to use and generate substances that possess little or no toxicity to
human health and the environment.
3.1.1.4.
Designing Safer Chemicals - Chemical products should be designed to affect their
desired function while minimizing their toxicity.
3.1.1.5.
Safer Solvents and Auxiliaries -The use of auxiliary substances (e.g., solvents,
separation agents, etc.) should be made unnecessary wherever possible and innocuous
when used.
3.1.1.6.
Design for Energy Efficiency -Energy requirements of chemical processes should
be recognized for their environmental and economic impacts and should be minimized. If
possible, synthetic methods should be conducted at ambient temperature and pressure.
3.1.1.7.
Use of Renewable Feedstock - A raw material or feedstock should be renewable
rather than depleting whenever technically and economically practicable.
3.1.1.8.
Reduce Derivatives - Unnecessary derivatization (use of blocking groups,
protection/ de-protection, temporary modification of physical/chemical processes) should
be minimized or avoided if possible, because such steps require additional reagents and
can generate waste.
3.1.1.9.
Catalysis - Catalytic reagents (as selective as possible) are superior to
stoichiometric reagents
3.1.1.10. Design for Degradation - Chemical products should be designed so that at the end
of their function they break down into innocuous degradation products and do not persist
in the environment
3.1.1.11. Real-time analysis for Pollution Prevention - Analytical methodologies need to be
further developed to allow for real-time, in-process monitoring and control prior to the
formation of hazardous substances
3.1.1.12. Inherently Safer Chemistry for Accident Prevention - Substances and the form
of a substance used in a chemical process should be chosen to minimize the potential
for chemical accidents, including releases, explosions, and fires
3.1.2
A Safety Data Sheet and a Technical Data Sheet shall be provided for all products to be considered.
3.2. REPORTING
Reports shall show all individual results (not averages) and display which test method was used.
“Pass or Fail” statement shall not be used. Actual values shall be reported. For Corrosion resistance,
specimens shall be tested to failure and actual defects shall be reported. For practical reasons, once
3000 hours has been reached, temporary results can be reported such as “No defects after 3000
hours.”
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© 2015 IAEGTM
PPRD
01-003
Issue
1d
Date 24th Nov 2015
4. TECHNICAL PERFORMANCE REQUIREMENTS
4.1. GENERAL
Test specimens shall be processed in accordance with the Technical Data Sheet which shall
describe each step of the process from cleaning to final curing of any paint applied. The process
parameters for all test pieces shall be recorded and reported.
We have separated this request into three parts:The section 4.2 gives acceptance criteria and associated test methods for 3 types of application:
Type A (section 4.2.1): application dominated by electrical conductivity requirements
Type B (section 4.2.2): application dominated by corrosion requirements but where no prior
etching is permitted
Type C (section 4.2.3): applications dominated by corrosion requirements that require an
aluminium etch prior to the application of a conversion coating.
.
4.2. TEST METHODS – ACCEPTANCE CRITERIA
4.2.1. Unpainted Chemical Conversion Coated alloy
4.2.1.1
Electrical Conductivity of Chemical Conversion Coated alloy
As determined by MIL DTL 81706 section 4.5.5. and shall be less than 5000µΩ prior to corrosion
testing and less than 10,000 µΩ after 336 hrs. of corrosion testing. Any recommended dwell time
prior to electrical testing must be specified by the manufacturer otherwise a default of 24 hrs. will be
used.
4.2.1.2
Corrosion resistance of unpainted Chemical Conversion Coated alloy
4.2.1.2.1 Option based upon ASTM B117 or ISO 9227
As an objective, test panels shall sustain exposure for 336 hours if tested to ASTM B117 or ISO
9227 however data illustrating the number of hours to failure would be preferred.
Panels shall be scribed with two (2) intersecting lines, 1/16th to 1/8th inch (1.6 to 3.2 mm) wide,
extending from corner to corner of the panel, through the coating and the pre-treatment and through
clad to the base metal.
The corrosion resistance evaluated on test pieces, shall comply with the following criteria:
- Show not more than 1 isolated corrosion spots or pits per 6 square inches (38.7 sq. cm) ,
none larger than 1/32 inch (0.8 mm) in diameter, on any one test piece.
-Corrosion pits originating from the electrical contact points, identification markings, or areas
within 1/16 inch (1.6 mm) of the contact point, or identification markings; and within ¼ inch
(6.4 mm) from the panel edges shall not be cause for rejection.
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© 2015 IAEGTM
PPRD
01-003
Issue
1d
Date 24th Nov 2015
Test specimen
Preferred Dimensions
Size:
Aluminium Al 2024 T3 bare
(unclad)
No. specimens
3 by 5 inch [75 x 125 mm]
or
3 by 10 inch [75 x 250 mm]
Thickness:
5
0.032 to 0.04 inch
[0.81 to 1.02 mm]
4.2.1.2.2
Option based upon ISO 21207, Annex A.
As an objective, test panels shall sustain exposure for 336 hrs. however data illustrating the
number of hours to failure would be preferred.
Panels are not scribed but
-should not show more than a total of 15 isolated corrosion spots or pits, none larger than
0.8mm (1/32 inch) in diameter in a total of 25 square centimetres (4 sq.in) of test area.
-should experience no greater than 3 gms in weight loss
Test specimen
Preferred Dimensions
Aluminium Al 2024 T3 bare
(unclad)
4.2.2
4.2.2.1
Size:
No. specimens
50x50mm [2 by 2 inch
Thickness:
0.96 to 1.04mm
5
[0.038 to 0.041 inch]
Chemical Conversion Coated alloy, no pre-etch and subsequently painted
Electrical Conductivity of Chemical Conversion Coated alloy
No requirement
4.2.2.2
Corrosion resistance of Chemical Conversion Coated alloy subsequently
painted
4.2.2.2.1 Option based upon ASTM B117 or ISO 9227
As a minimum, test panels shall sustain exposure for the number of hours indicated below, however
data illustrating the number of hours to failure would be preferred.
The corrosion resistance evaluated on test pieces, shall comply with the following criteria:
- Show not more than 1 isolated corrosion spots or pits per 6 square inches (38.7 sq. cm) , none
larger than 1/32 inch (0.8 mm) in diameter, on any one test piece.
-Corrosion pits originating from the electrical contact points, identification markings, or areas within
1/16 inch (1.6 mm) of the contact point, or identification markings; and within ¼ inch (6.4 mm) from
the panel edges shall not be cause for rejection.
For alloy 2024T3 and after 3,000 hours of exposure:
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© 2015 IAEGTM
PPRD
01-003
Issue
1d
Date 24th Nov 2015
Test specimen
Preferred Dimensions
No.
specimens
Aluminium Al 2024 T3 bare
Size: 4X6 in or 3X5 in or 3X10 in.
(unclad)
Thickness: 0.032 to 0.040 in
5
plus one layer of Chrome free
epoxy primer of no more than 35
microns in thickness
For alloy 6061T6 or 6082 T6 or 7075T6 and after 1,600 hours of exposure:
Aluminium Al 6061T6, 6082T6 or
Size: 4X6 in or 3X5 in or 3X10 in.
7075T6
Thickness: 0.032 to 0.040 in
5
plus one layer of Chrome free
epoxy primer of no more than 35
microns in thickness
4.2.2.2.1 Option based upon ISO 21207
As an objective, test panels shall sustain exposure for 504hrs. however data illustrating the
number of hours to failure would be preferred.
Panels are not scribed but
-should not show more than a total of 15 isolated corrosion spots or pits, none larger than
0.8mm (1/32 inch) in diameter in a total of 25 square centimetres (4 sq.in) of test area.
-should experience no greater than 10gms in weight loss
For alloy 2024T3 and after 504 hours of exposure:
Test specimen
Preferred Dimensions
Aluminium Al 2024 T3 bare
(unclad)
Size:
Thickness:
plus one layer of Chrome free
No. specimens
50x50mm [2 by 2 inch
0.96 to 1.04mm
[0.038 to 0.041 inch]
5
epoxy primer of no more than 35
microns in thickness
For alloy 6061T6 or 6082 T6 or 7075T6 and after 336 hours of exposure:
Aluminium Al 6061T6, 6082T6 or
7075T6
Size:
Thickness:
plus one layer of Chrome free
50x50mm [2 by 2 inch
5
0.96 to 1.04mm
[0.038 to 0.041 inch]
epoxy primer of no more than 35
microns in thickness
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© 2015 IAEGTM
PPRD
01-003
Issue
1d
Date 24th Nov 2015
4.2.2.3
Wet and Dry Paint adhesion for Chemical Conversion Coated alloy subsequently
painted
ASTM D3359 or ISO 2409 methods shall be used. Test conditions are 6X6 or 11X11 intersecting
lines at 90 degrees. For wet adhesion, a 14 day immersion is required. Wet cotton ball patches may
be used as long as the surface remains wet. Tape contact time 1 to 5 minutes. Any recommended
dwell time prior to electrical testing must be specified by the manufacturer otherwise a default of 24
hrs. will be used.
4.2.2.3.1
Dry adhesion
There shall not loss of adhesion (5B for ASTM, 0 for ISO).
4.2.2.3.2
Wet adhesion
There shall not loss of adhesion (5B for ASTM, 0 for ISO) or blisters or bubbling on the surface.
There shall not be any evidence of corrosion in the scribes or corrosion or blisters extending further
than 0.05 inch [1.25 mm] on either side of the scribes after 3,000 hours of exposure.
Test specimen
Dimensions
Aluminium Al 2024 T3 bare (unclad) +
-Chrome free corrosion-inhibiting primer 1.38 mils
No. specimens
2 Dry
Size: 4X6 in or 3X5 in or 3X10 in.
2 Wet
(35 μm) thickness maximum
Thickness: 0.032 to 0.040 in
4.2.3
Chemical Conversion Coated alloy, pre-etched and subsequently painted
The supplier shall use an acid deoxidizer that gives a total metal removal of 0.02 to 0.15 mils (0.5 to
3.8 microns) per surface.
4.2.3.1
Electrical Conductivity of Chemical Conversion Coated alloy
No requirement
4.2.3.2
Corrosion resistance of Chemical Conversion Coated alloy subsequently
painted
4.2.2.2.1 Option based upon ASTM B117 or ISO 9227
As a minimum, test panels shall sustain exposure for the number of hours indicated below, however
data illustrating the number of hours to failure would be preferred.
The corrosion resistance evaluated on test pieces, shall comply with the following criteria:
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© 2015 IAEGTM
PPRD
01-003
Issue
1d
Date 24th Nov 2015
- Show not more than 1 isolated corrosion spots or pits per 6 square inches (38.7 sq. cm) , none
larger than 1/32 inch (0.8 mm) in diameter, on any one test piece.
-Corrosion pits originating from the electrical contact points, identification markings, or areas within
1/16 inch (1.6 mm) of the contact point, or identification markings; and within ¼ inch (6.4 mm) from
the panel edges shall not be cause for rejection.
For alloy 2024T3 and after 3,000 hours of exposure:
Test specimen
Preferred Dimensions
No.
specimens
Aluminium Al 2024 T3 bare
Size: 4X6 in or 3X5 in or 3X10 in.
(unclad)
Thickness: 0.032 to 0.040 in
5
plus one layer of Chrome free
epoxy primer of no more than 35
microns in thickness
For alloy 6061T6 or 6082 T6 or 7075T6 and after 1,600 hours of exposure:
Aluminium Al 6061T6, 6082T6 or
Size: 4X6 in or 3X5 in or 3X10 in.
7075T6
Thickness: 0.032 to 0.040 in
5
plus one layer of Chrome free
epoxy primer of no more than 35
microns in thickness
4.2.2.2.1 Option based upon ISO 21207
As an objective, test panels shall sustain exposure for 504hrs. however data illustrating the
number of hours to failure would be preferred.
Panels are not scribed but
-should not show more than a total of 15 isolated corrosion spots or pits, none larger than
0.8mm (1/32 inch) in diameter in a total of 25 square centimetres (4 sq.in) of test area.
-should experience no greater than 10gms in weight loss
For alloy 2024T3 and after 504 hours of exposure:
Test specimen
Preferred Dimensions
Aluminium Al 2024 T3 bare
(unclad)
Size:
Thickness:
plus one layer of Chrome free
No. specimens
50x50mm [2 by 2 inch
0.96 to 1.04mm
[0.038 to 0.041 inch]
5
epoxy primer of no more than 35
microns in thickness
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© 2015 IAEGTM
PPRD
01-003
Issue
1d
Date 24th Nov 2015
For alloy 6061T6 or 6082 T6 or 7075T6 and after 336 hours of exposure:
Aluminium Al 6061T6, 6082T6 or
7075T6
Size:
Thickness:
plus one layer of Chrome free
50x50mm [2 by 2 inch
5
0.96 to 1.04mm
[0.038 to 0.041 inch]
epoxy primer of no more than 35
microns in thickness
4.2.3.3
Wet and Dry Paint adhesion for Chemical Conversion Coated alloy subsequently
painted
ASTM D3359 or ISO 2409 methods shall be used. Test conditions are 6X6 or 11X11 intersecting
lines at 90 degrees. For wet adhesion, a 14 day immersion is required. Wet cotton ball patches may
be used as long as the surface remains wet. Tape contact time 1 to 5 minutes. Any recommended
dwell time prior to electrical testing must be specified by the manufacturer otherwise a default of 24
hrs. will be used.
4.2.3.3.1
Dry adhesion
There shall not loss of adhesion (5B for ASTM, 0 for ISO).
4.2.3.3.2
Wet adhesion
There shall not loss of adhesion (5B for ASTM, 0 for ISO) or blisters or bubbling on the surface.
There shall not be any evidence of corrosion in the scribes or corrosion or blisters extending further
than 0.05 inch [1.25 mm] on either side of the scribes after 3,000 hours of exposure.
Test specimen
Dimensions
Aluminium Al 2024 T3 bare (unclad) +
-Chrome free corrosion-inhibiting primer 1.38 mils
No. specimens
2 Dry
Size: 4X6 in or 3X5 in or 3X10 in.
2 Wet
(35 μm) thickness maximum
Thickness: 0.032 to 0.040 in
4.2.4
Visual aspect for both cases
When examined with an unaided eye, the film shall be continuous, smooth, and adherent indicating
that it is free of powdery areas, burnings, blisters and discontinuities such as scratches, ruptures or
other damages.
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© 2015 IAEGTM
PPRD
01-003
Issue
1d
Date 24th Nov 2015
4.2.5
Temperature Resistance
The chemical conversion coating should be capable of maintaining performance after 6 hrs exposure
to 125C.
4.2.6
Film weight or thickness for all cases
The range of film weight or thickness shall be specified by the manufacturer
4.2.7
Touch-up Procedure
Shall be specified by the manufacturer
4.2.8
Chemical Resistance of Chemical Conversion Coating
Shall be specified by the manufacturer
5
REFERENCES
Document No.
Title
ASTM B117
Standard Practice for Operating Salt Spray (Fog) Apparatus
ASTM D3359
Standard Test Methods for Measuring Adhesion by Tape Test
ISO 1463
Metallic and oxide coatings -- Measurement of coating thickness -Microscopical method
ISO 2360
Non-conductive coatings on non-magnetic electrically conductive basis
materials -- Measurement of coating thickness -- Amplitude-sensitive
eddy-current method
ISO 2409
Paints and varnishes -- Cross-cut test
ISO 9227
Corrosion tests in artificial atmospheres -- Salt spray tests
ISO 21207
Corrosion tests in artificial atmospheres- Accelerated corrosion tests
involving alternate exposure to corrosion-promoting gases, neutral
salt-spray and drying
ISO 6272
Paints and varnishes -- Rapid-deformation (impact resistance) tests
MIL_DTL 5541
Chemical conversion coatings on Aluminium and Aluminium alloys
MIL DTL 81706
Chemical conversion materials for coating Aluminium and Aluminium
alloys
(1)
Document1
Anastas, P. T.; Warner, J. C. Green Chemistry: Theory and Practice,
Oxford University Press.
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© 2015 IAEGTM
PPRD
01-003
Issue
1d
Date 24th Nov 2015
6. GLOSSARY
OEM
Original Equipment Manufacturer
PRD
Performance Requirement Document
7. REVISION HISTORY
Version
Date
1a
15-Oct 2015
1b
24-Nov 2015
Document1
Name
Description
IAEG™_WG2
W. Lampa
Dave Sidgwick
Initial draft taking into account the results from
WG2 meeting on 13th Oct 15
Revision “ready to distribute to WG2 members”
for amendments / modifications to chapter 4
(engineering requirements)
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© 2015 IAEGTM