ISO 17212:2004

INTERNATIONAL ISO
STANDARD 17212
First edition
2004-05-15
Structural adhesives — Guidelines for the
surface preparation of metals and
plastics prior to adhesive bonding
Adhésifs structuraux — Lignes directrices pour la préparation de
surface de métaux et de plastiques avant le collage par adhésif

Reference number
©
ISO 2004
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©  ISO 2004
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ii © ISO 2004 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 3
3 Terms and definitions. 3
4 Safety. 3
5 Initial preparative techniques . 4
5.1 General. 4
5.2 Handling, cleaning and storing . 4
6 Surface modification. 5
6.1 Physical: Mechanical (scarification) . 5
6.2 Physical: Non-mechanical. 6
6.3 Chemical . 7
6.4 Combined procedures . 9
7 Preparative procedures. 10
7.1 General. 10
7.2 Specific. 11
8 Evaluation of durability . 27

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 17212 was prepared by Technical Committee ISO/TC 61, Plastics, Subcommittee SC 11, Products.
It cancels and replaces ISO 4588:1995 and ISO 13895:1996, which have been technically revised.
iv © ISO 2004 – All rights reserved

Introduction
Some materials will bond far better than others will and some will not bond at all without special treatment.
The suitability of a surface for bonding depends upon the degree of surface preparation, the joint’s design, the
function it has to perform (joining, sealing, etc.) and the environment it has to perform in.
Prior to bonding, some degree of surface preparation is required for most adhesives — but not all. Material
surfaces that are particularly prone to weak or loose surface layers, stress cracking or solvent attack usually
require special treatment.
Following appropriate preparation, most common metals can be bonded satisfactorily. Were it not for
contamination and residual mould release agents, the thermoset plastics (e.g. polyepoxy and polyester
composites) would bond well without any preparation. By contrast, most thermoplastics require careful
preparation because of their low surface energy.
Some paints — especially the cataphoretic, water-based primers used by the vehicle industries — can provide
an excellent surface. However, the stability of the interface below the paint should be checked. The surface of
the paint itself, even if fresh, can require treatment in order to raise its free energy and thus facilitate wetting.
Certain adhesives possess the ability to dissolve light oils and some polymeric materials. Consequently, for
joints that are not “safety-critical” some surfaces do not require any preparation prior to bonding.
In order to achieve the optimum environmental durability from a bonded joint, the traditional preparative
approach usually, though not necessarily, consisted of three sequential steps:
 the removal of contaminants;
 physically induced modification of the surface;
 chemical treatment.
However, legislative pressure is driving development and the introduction of new methods. Consequently, the
separate steps of the foregoing sequence are being combined and the more hazardous chemicals are being
progressively eliminated.
The majority of both thermoset and thermoplastics materials can be prepared by commonly applicable
techniques — though there will often be detailed differences. By contrast, metal surfaces generally require
individual treatment. The optimization of the durability of a metal-based joint usually requires the introduction
of progressively more complex and specific treatments.
Such process options are described for a number of metals and some plastics (see Clause 7).

INTERNATIONAL STANDARD ISO 17212:2004(E)

Structural adhesives — Guidelines for the surface preparation
of metals and plastics prior to adhesive bonding
1 Scope
1.1 General
This International Standard provides and describes the usual procedures for the preparation of component
surfaces prior to bonding for either laboratory evaluation or the process of construction. This International
Standard is applicable to metal and plastic surfaces that are commonly encountered.
1.2 Surfaces
These comprise the following metal and plastic families — the latter including filled versions and suitable
paints:
Metals
aluminium
chromium
copper
magnesium
nickel
steel (mild)
steel (stainless)
tin
titanium
zinc
Paints
cataphoretic (water-based)
poly-alkyd
ester
epoxide
urethane
Plastics
Thermoplastic
acrylonitrile-butadiene-styrene copolymer
poly-acetal
acrylate
amide
carbonate
ester
ether ether ketone
ethylene
imide
methyl methacrylate
phenylene oxide
propylene
styrene
tetrafluoroethylene
vinyl chloride
sulfone
Thermoset
poly-alkyd
allyl phthalate
amino
epoxide
ester
phenolic
urethane
urea-based (see poly-amino above)
1.3 Methods
The various techniques described for cleaning and modifying surfaces are drawn from the best of current
practice. The methods can be used in a variety of combinations to create the most effective preparative
process conducive with the environmental durability required of the bonded joint.
2 © ISO 2004 – All rights reserved

2 Normative references
The following referenced documents are indispensable for the application of this document. For dated
references, only the edition cited applies. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 472, Plastics — Vocabulary
EN 923, Adhesives — Terms and definitions
BS 5350-C5, Methods of test for adhesives — Determination of bond strength in longitudinal shear for rigid
adherends
3 Terms and definitions
For the purposes of this document, the terms and definitions in ISO 472 and EN 923, together with the
following, apply.
3.1
plastic
material which contains, as an essential ingredient, a high polymer and which, at some stage in its processing
into finished products, can be shaped by flow
NOTE 1 For the specific requirements of this International Standard, “plastic” also includes paint. In this latter context, it
needs be realized that only a few paint surfaces are capable of supporting anything other than purely nominal loads. The
exceptions are typically those based upon aqueous, electrochemical paints — such as those used in the automotive
industries — and the acrylic, epoxy and polyester-based paints used during the preparation of “pre-coated” metal sheet.
NOTE 2 In some countries, the use of the term “plastics” as the singular form as well as the plural form is permitted.
3.2
scarification
shallow roughening of both metallic and plastic (including paint) surfaces, using either abrasion or blasting,
almost invariably improving the performance of the final bonded joint
4 Safety
Users of this International Standard shall be familiar with normal laboratory practice and the principles of good
industrial hygiene.
Users shall be aware that this International Standard does not purport to address all safety problems, and it is
their responsibility to establish practices which are compliant with relevant national health, safety and
environmental legislation.
Concentrated acids, alkalis and oxidizing agents (e.g. chromium trioxide, dichromates and chrome-based
solutions) are all highly corrosive chemicals. Splashes can cause severe damage to both skin and eyes and
will damage normal clothing. Protective clothing (e.g. overalls, gloves and goggles or visors) shall always be
worn when using these chemicals.
Similarly, appropriate precautions shall be taken when using solvents. At a minimum, eye protection and
gloves (or appropriate barrier cream) shall be worn.
Wherever possible, use propan-2-ol as a solvent. Otherwise, a ketone (acetone or methyl ethyl ketone) or,
though deprecated, a halogenated solvent, that meets the requirements of the Montreal Protocol and national
legislative requirements, can be used. Alcohols and ketones are flammable — particularly ketones. All such
materials are narcotic in concentration. Ventilate properly, take account of vapour density and draw fumes
away from the operator.
Do not allow any cleaning materials to contact the skin. Abuse can lead to dermatitis.
Some of the methods given below employ dangerous techniques, materials and proprietary chemicals. It is
essential therefore that the supplier's instructions be followed, health and safety data studied, and appropriate
safety procedures established.
Waste and spent materials shall be disposed of in accordance with national legislative requirements through
the services of an authorized disposal organization — whose advice shall always be sought.
WARNING — When making up solutions:
 NEVER POUR WATER INTO ACID.
 ALWAYS ADD ACID IN A SLOW STEADY STREAM TO A STIRRED SOLUTION.
An exothermic reaction can heat the resulting mixture. If this occurs, contamination hazards will be
intensified. TAKE GREAT CARE.
5 Initial preparative techniques
5.1 General
When safety-critical structures are being bonded, optimum treatment is always necessary. This requires the
use of appropriate techniques to both clean and modify the surface, which itself can be either an inorganic or
an organic coating — or even a combination of both. By contrast, when joints are only to be lightly or
nominally loaded, the use of adhesives capable of dissolving light oils can allow minimal, or even no, surface
preparation. The manufacturer’s advice shall always be sought.
5.2 Handling, cleaning and storing
5.2.1 Handling
Component areas which are to be bonded shall be handled as little as possible prior to preparation. After
preparation, such areas shall not be handled directly at all. However, if this is unavoidable then clean, lint-free
cotton or nylon gloves shall be worn.
5.2.2 Cleaning
Remove oil- and grease-based residues using aqueous materials if possible. Non-ionic detergents give good
results. Proprietary alkaline cleaners are particularly good for metals because not only can they remove
hydrocarbons but the more aggressive, stronger, versions can also remove metallic soaps and salts. However,
the latter shall not be used on aluminium and care shall be taken to ensure that this metal is not exposed to
cleaners based on sodium hydroxide. Some proprietary mixtures are used hot while others utilize either
anodic or a cathodic currents. Whichever cleaning agent is used, components shall always be rinsed
thoroughly and dried in a stream of warm, dry air for about 10 min at 60 °C.
If solvents need to be used to remove identification marks, or paint, then propan-2-ol shall be used wherever
possible. Alternatively, use acetone, methyl ethyl ketone or another permitted solvent (see Clause 4). Solvents
can severely damage some thermoplastic materials by either dissolving them or initiating stress cracking.
Polycarbonate, poly(methyl methacrylate) and acrylonitrile-butadiene-styrene copolymer based plastics are
particularly susceptible in this latter regard.
Ultrasonic cleaning can prove acceptable for the preparation of smaller components.
The use of a vapour bath is generally deprecated, but is recommended for the preparation of titanium and its
alloys. However, chlorinated solvents shall not be used in this instance.
4 © ISO 2004 – All rights reserved

It shall not be forgotten that some industrial processes can, and do, have a damaging effect on surfaces, both
during and after their preparation. The use of equipment often releases deleterious dust, fumes and vapours
into the air. Oil vapour, mould release agent sprays and the atmosphere of a plating shop are particularly
detrimental. Consequently, surface preparation (and bonding) shall be effected in separate areas where such
contamination can be avoided.
5.2.3 Storing
A distinction needs to be made between laboratory storage and the delays incurred during industrial
production. The former implies performance qualification of either surface or adhesive. Where qualification is
required, storage shall be maintained in an ambient atmosphere of (23 ± 2) °C with a relative humidity of
(50 ± 5) %. The components shall be used within 8 h, except for those materials, such as mild steel, which are
still liable to prejudicial oxidation. Such surfaces shall be bonded as soon as possible after preparation and,
prior to bonding, shall always be maintained in a dry atmosphere. Wherever practical, parts shall not be
touched and shall be kept in a closed container or under a suitable non-contaminating cover such as
unbleached Kraft paper.
Industrial production requires that minimum performance standards be maintained. To this end, procedures
shall be established such that the integrity of a prepared surface is not unacceptably prejudiced prior to
assembly. Particular regard shall be paid to the possibility of damage occurring through oxidation,
condensation and contamination — particularly by release agents, which shall never be used in the same
building. Ideally, parts shall be bonded immediately after preparation and only exceptionally after 4 h.
6 Surface modification
6.1 Physical: Mechanical (scarification)
6.1.1 Abrasion
Abrasion can be effected either wet or dry using either a water-resisting, coated paper (45 µm to 106 µm grit)
or a non-woven, abrasive fabric.
The following sequence shall be employed:
a) Abrade straight across in a convenient direction until all the surface has been lightly and uniformly
scarified.
b) Then abrade similarly at right angles until all traces produced in operation a) have been obliterated.
c) Then abrade by means of a circular (u 100 mm diameter) motion until, again, all traces of the foregoing
operation b) have been obliterated and the surface appears uniform.
d) Remove debris. If dry-abraded, and if practical, use a vacuum. Otherwise, blow-clean in a suitably
ventilated enclosure with clean, dry air. If wet-abraded, solvent-wipe using a clean, lint-free cloth and
allow to dry.
e) Then either bond or implement a further surface modification process.
If parts are to be bonded, then they shall be dry and shall be bonded as soon as practical and preferably
within one minute (see 5.2.3). Drying can be speeded by the use of a warm, dry air stream at a temperature
not exceeding 65 °C.
NOTE 1 Care should be exercised to ensure that abrasives do not become clogged and that contaminants are not
being transferred from step to step through the above sequence.
NOTE 2 See 6.3.2 e) — the “water-break test” — a procedure that demonstrates that a component’s surface is free of
contamination.
6.1.2 Blasting
Dry blasting is usually reserved for metallic components. However, when used carefully — to avoid excessive
erosion — the less aggressive processes can be effective when used on the more robust plastics. Proprietary
processes are available. These encompass such specialized grits as particulate carbon dioxide and shredded
nut husks. However, in the main, metallic components are usually prepared by dry blasting with 45 µm to
106 µm abrasive grit until the surface is uniform in appearance. Neither iron- nor steel-based grits shall be
used on aluminium, copper, stainless-steel or titanium parts.
Wet blasting normal to the surface, using u 16,8 µm grit, suspended in either water or steam, can be
particularly effective on small metallic parts. Proprietary systems usually contain water-soluble additives. For
this reason, the manufacturer’s advice shall be sought in order to prevent further contamination of the surface.
Wet blasting is not yet recommended for titanium.
Whichever technique is used, steps 6.1.1 d) and 6.1.1 e) shall be implemented.
6.2 Physical: Non-mechanical
A number of processes have been developed whose purpose is to modify a surface without using either
mechanical abrasion or liquid-based chemical techniques. Mainly, these are dedicated to bringing about a
beneficial chemical modification of the surfaces of the plastics by physically induced, oxidative processes.
Some of these processes can also remove modest levels of contamination.
The two major examples of these specialized techniques are the plasma discharge and flame treatments. As
optimum conditions need to be developed for both, it is suggested that appropriate techniques be devised in
conjunction with an equipment supplier and a recognized investigative laboratory.
The following comments could be helpful:
a) Surface modification induced by an oxidative gas flame is a relatively simple, fast, effective and economic
means of improving the surfaces of a wide variety of plastics. The process has the very useful advantage
of being able to cope with rapid changes in component topography.
b) Similarly, plasma discharge at ambient pressure — often called corona discharge — is fast, effective and
economic. However, the technique has a restricted ability to cope with a varying component topography.
Consequently, equipment can be troublesome to adjust and it can be difficult to maintain performance
unless components are simple in shape and essentially flat.
c) Low-pressure plasma discharge processes can be considered to be more versatile in their nature than
the use of flame oxidation. Complex shapes generally present no problems and surface modification can
be optimized by the use of different gas combinations in the discharge chamber. However, the
attractiveness of the technique is diminished by the high capital cost of equipment and the fact that, unlike
gas flame and corona-based methods — which can be run continuously — plasma chambers require a
batch-based process.
d) Lasers have been used to prepare both plastics and metal surfaces. However, as the technique is not yet
considered to be sufficiently well developed, it should only be considered when there are no alternatives.
e) None of the foregoing methods involves liquids. Therefore, the need to dry treated surfaces is avoided.
However, depending on the process used, the nature of the surface itself and the ambient environment,
the manner of surface deterioration will vary. Some combinations of the foregoing variants can be very
tolerant but, in principle, all surfaces shall be bonded as soon as practical after treatment (see 5.2.3).
6 © ISO 2004 – All rights reserved

6.3 Chemical
6.3.1 Background
The usual object of chemical treatment is to oxidize a surface that has been cleaned in accordance with 5.2.2
and scarified in accordance with 6.1.1 and 6.1.2. However, as oxidation usually requires the use and disposal
of powerful oxidizing agents, alternative approaches using coupling agents have been, and are still being,
developed. To date, they have tended to be based upon silane chemistry. These processes, which are largely
proprietary, are discussed separately in 6.4.
Table 1 — Basis of preparative methods for metals and their alloys
Metals and alloys Procedure Notes
Aluminium and alloys De-grease (5.2.2) and scarify (6.1), Alternatively, coupling agents can be used (see 6.4).
then bond after etching as required
in 7.2.1.1.
Anodized: For all anodized surfaces, preferably bond within 4 h.
Normal (prepared by De-grease (5.2.2) and abrade lightly
either the chromic or the (6.1.1), then bond.
sulfuric acid processes)
Hard-anodized Blast (6.1.2) and bond after etching This surface shall not be bonded without the further
as required by 7.2.1.2. treatment described here. Hence, the requirement to
strip the surface. Coupling agents can also be used
(see 6.4).
Phosphoric acid anodized Proprietary Follow proprietary process before bonding.
Chromium De-grease (5.2.2), then bond
following either scarification (6.1) or
etching as required in 7.2.1.3.
Copper (including brass and De-grease (5.2.2), then bond Any one of the three etch solutions described can be
bronze) following either scarification (6.1) or used.
etching as required in 7.2.1.4.
Magnesium De-grease (5.2.2), then bond after UNDER NO CIRCUMSTANCES SHALL THIS
proceeding as required in 7.2.1.5. METAL BE SCARIFIED, ABRADED OR BLASTED.
DO NOT EXPOSE TO THE ATMOSPHERE OF A
VAPOUR BATH.
Nickel De-grease (5.2.2), then bond Any one of the three etch solutions described can be
following either scarification (6.1) or used.
etching as required in 7.2.1.6.
Steel (mild) De-grease (5.2.2), then bond Coupling agents can also be used and are the
following either scarification (6.1) or preferred method (see 6.4).
etching as required in 7.2.1.7.
Steel (stainless) De-grease (5.2.2), then bond Coupling agents can also be used and are the
following either scarification (6.1) or preferred method (see 6.4).
etching as required in 7.2.1.8.
Tin De-grease (5.2.2), then bond See also 7.2.1.9.
following either abrasion (6.1.1) or
dry blasting (6.1.2).
Titanium Vapour de-grease (5.2.2), then This metal is usually used for safety-critical
bond following the special aerospace purposes. The provisions set out in
techniques set out in Method 1 or 2 7.2.1.10 shall be considered.
of 7.2.1.10.
Zinc De-grease (5.2.2), then bond Coupling agents can also be used and are the
following either scarification (6.1) or preferred method (see 6.4).
etching as required in 7.2.1.11.
Table 2 — Basis of method for plastics, including paints
Plastics, including paints Procedure Notes
Paints:
Cataphoretic
Some polyester paints have proved difficult
Poly-alkyd
All are usually prepared by cleaning to bond and some formulations could well
and scarifying (see 5.2.2 and 6.1). benefit from flame- or plasma-based
ester
techniques (see 6.2).
epoxide
urethane
Thermoplastic plastics:
Acrylonitrile-butadiene-styrene
copolymer
Those plastics in this group that do not
The chemical treatments cited below have
Poly-acetal
dissolve readily in common solvents also been developed for the following
can prove difficult to bond — even with
thermoplastic materials and their use could
acrylate
acrylic-based adhesives. Usually, prove beneficial if difficulties are
performance will be substantially
amide encountered with other methods:
improved following treatment with
butylene terephthalate (BTP)
flame- or plasma-based techniques
(see 6.2).
carbonate
Acrylonitrile-butadiene-styrene copolymer
ester
see 7.2.2.1
ether ether ketone
Poly-acetal see 7.2.2.2
ethylene
amide see 7.2.2.3
imide
butylene terephthalate see 7.2.2.4
ethylene see 7.2.2.5
methyl methacrylate
propylene see 7.2.2.6
phenylene oxide
tetrafluoroethylene see 7.2.2.7
propylene
styrene
sulfone
tetrafluoroethylene
vinyl chloride
Thermoset plastics:
The durability of joints based on these
Cellulose-based esters (see
materials is likely to be improved by one or
Note 1)
more of the combined techniques
described in 6.4.
Poly-alkyd
Note also:
allyl phthalate
1) If bonding with epoxy-based adhesive,
amino
All are usually prepared by cleaning heat for 1 h at 93 °C prior to bonding and
and scarifying (see 7.2.2 and 6.1). bond while still warm. Avoid premature
epoxide (see Note 2)
curing of hot adhesive.
ester (see Notes 3 and 4)
2) If bonding hot, ensure that surface
water has been expelled before bonding.
phenolic
3) Use lower-modulus adhesives to
urethane
improve load distribution on brittle gel-coat
surfaces.
urea-based (see poly-amino
above)
8 © ISO 2004 – All rights reserved

6.3.2 Chemical reagents and solutions
The effectiveness of the chemical-based surface modification processes depends upon the maintenance of
the integrity of the individual process. Professional advice could prove advantageous, especially in relation to
the maintenance of etch solutions. The points expressed in the following requirements shall be observed.
Requirements:
a) The water used shall be either distilled or de-ionized and shall not contain more than 50 mg/kg of solids.
Its pH-value shall lie between 6,5 and 8,5 and its conductance shall be less than 20 µS.
b) Solutions shall be made up accurately (technical or reagent grade materials, to an accuracy of ± 1 %) and
maintained by means of periodic sampling, analysis and relevant documentation. Whenever solutions
need to be made up, or utilized, then only equipment made from polyethylene, polypropylene or
tetrafluoroethylene shall be used.
c) Waste and spent materials, chemicals and other solutions shall be disposed of in accordance with legal
requirements and through the services of an authorized disposal organization, whose advice shall always
be sought.
d) Rinsing shall be conducted by either spraying or dipping in a constantly refreshed water tank — see
requirement a). In both cases, the action shall be sufficiently vigorous to ensure thorough removal of all
residues.
e) The “water-break” test will indicate whether the surface is clean and is conducted by immersing the
surface in water — see requirement a). Following withdrawal, the ensuing water film shall remain
continuous and unbroken for 30 s. If this condition is met, the surface can be assumed to be clean and in
an optimum condition for bonding. However, although long-term durability will be enhanced,
improvements in bond strength should not be anticipated.
6.4 Combined procedures
6.4.1 Introduction
A number of preparative techniques have been developed in which scarification is combined with a chemical
treatment that is usually, though not necessarily, associated with the use of a silane-based coupling agent.
6.4.2 Dry techniques
6.4.2.1 Background
Dry techniques are applicable to both metal and plastics surfaces. The two methods available are based on
proprietary processes. The manufacturer or supplier shall be consulted with regard to the selection of a
specific process for a chosen surface.
6.4.2.2 Silane-coated abrasive
The surface is blasted with a silane-coated abrasive — usually corundum — following, if required, cleaning
and scarification (see 5.2.2 and 6.1). Dependent upon the proprietary method actually used, it could be
necessary to follow this treatment with a process-specific primer prior to bonding.
6.4.2.3 Flame treatment
Following the manufacturer's instructions, the appropriately prepared surface (see 5.2.2 and 6.1) is chemically
modified by exposing it to a flame comprising the combustion products of a proprietary material.
6.4.3 Wet techniques
6.4.3.1 Background
The two wet techniques are similar in principle, but can differ widely in the materials used — though often,
these will still be based on silane, or related, coupling agents. Both techniques are suitable for metals and
plastics and both rely on proprietary materials. Consequently, the manufacturer or supplier shall be consulted
with regard to the suitability of a specific process for a chosen surface.
6.4.3.2 Modification during abrasion
Here, following initial cleaning (see 5.2.2), the surface is abraded wet, in accordance with the requirements of
6.1.1 up to and including 6.1.1 c). Thereafter, the proprietary process is introduced and the manufacturer's
instructions followed to the commencement of the bonding process itself.
Some of the essentially aqueous solutions available will also indicate whether a surface is actually in a
condition suitable for bonding. This is achieved by matching the surface tension of the liquid to that of the
adhesive to be used.
6.4.3.3 Modification after abrasion
Here, following cleaning and scarification in accordance with 5.2.2 and 6.1, the proprietary process is
introduced, as required by the manufacturer, prior to bonding.
7 Preparative procedures
7.1 General
Table 1 (metals) and Table 2 (plastics) summarize the preparative procedures available for the more
commonly used materials. It will be seen that, for the optimization of joint durability, all metals require a
specific, individual treatment. Plastics, by comparison, do not, and similar, if not identical, methods can be
used to prepare several different polymer types. In addition, most plastics can be prepared without recourse to
a hazardous wet-chemical process.
Most thermoset plastics surfaces are usually, and adequately, treated by degreasing and scarifying using
appropriate and convenient processes chosen from 5.2.2, 6.1.1 and, particularly, 6.2.
The majority of the low surface energy, thermoplastic materials can usually be prepared by employing either
of the two methods — plasma or flame — described in 6.2. Unless their surfaces are contaminated with mould
release agent, or have become soiled, freshly made parts will not require cleaning as both treatments can
cope with minor levels of contamination. If cleaning is necessary, then care needs to be exercised to ensure
that the plastic materials are not damaged. If at all possible, solvents should be avoided as these can have a
particularly deleterious effect, e.g. stress cracking and partial dissolution (see 5.2.2). Scarifying will not
normally be required.
However, some specific chemical treatments have been developed for individual thermoplastics and these
can prove helpful in cases of difficulty.
The following subclauses shall be read in conjunction with the comments given in 6.3.2.
10 © ISO 2004 – All rights reserved

7.2 Specific
7.2.1 Metals
7.2.1.1 Aluminium and alloys
7.2.1.1.1 General
The five methods presented below increase progressively in complexity and, with that, the probability that they
will enhance the durability of the ensuing joint. Method 1 is the minimum preparation that shall be considered
and is best considered only for indoor applications. Method 2 is effective and can be considered for non-
critical, temperate-zone applications. Method 3 has been found to be generally effective. Methods 4 and 5 are
currently used in the construction of aircraft and associated structures.
7.2.1.1.2 Procedures
a) Method 1:
 Remove oil or grease contamination (see 5.2.2).
 Scarify by abrading or blasting with alumina grit (see 6.1.1 and 6.1.2).
 Bond as soon as possible after drying and preferably within 4 h. Alternatively, coat the surface with an
adhesive-compatible primer — consult the adhesive manufacturer.
b) Method 2:
 Remove oil or grease contamination (see 5.2.2).
 Following scarification with an alumina-based grit (6.1), use a proprietary etch in accordance with the
manufacturer's instructions.
 Bond as soon as possible after drying and preferably within 4 h. Alternatively, coat the surface with an
adhesive-compatible primer — consult the adhesive manufacturer.
c) Method 3:
 Remove oil or grease contamination (see 5.2.2).
 Either in conjunction with, or following, scarification with an alumina-based grit (see 6.1), use a proprietary
coupling agent in accordance with 6.4.2 or more usually 6.4.3.
 Bond as soon as possible after drying and preferably within 4 h. Alternatively, coat the surface with an
adhesive-compatible primer — consult the adhesive manufacturer.
d) Method 4:
 Remove oil or grease contamination (see 5.2.2).
 Scarify by abrading or blasting with alumina grit (see 6.1.1 and 6.1.2).
 Immerse the item to be etched for 10 min at (68 ± 3) °C in the etch solution (7.2.1.1.3).
 Remove the item, wash with tap water and rinse thoroughly in cold distilled or de-ionized water.
 Conduct the “water-break” test.
 Drain for 15 min.
 Dry with warm, dry air for about 10 min at a temperature not exceeding 60 °C.
 Bond as soon as possible after drying and preferably within 4 h. Alternatively, coat the surface with an
adhesive-compatible primer — consult the adhesive manufacturer.
NOTE Some special variations of this etching procedure will produce surfaces that can be successfully bonded after
both oiling and forming. However, it should be generally assumed that conventionally treated surfaces are readily
damaged and should not be touched, even when gloves are worn, if very high performance, safety-critical structures are
being created.
7.2.1.1.3 Etch solution
Before commencing, see Clause 4 and requirements a) to e) of 6.3.2.
The composition of the etch solution is as follows:
Table 3 — Composition of the etch solution for aluminium and alloys (non-anodized)
Reagent (technical or reagent grade) Parts by mass (±± 1 %)
±±
Potassium dichromate or sodium dichromate 1,0
Concentrated sulfuric acid (ρ = 1,84 g/ml) 10,0
Distilled/de-ionized water 30,0

Prepare the solution as follows: with constant stirring, cautiously add the acid to 60 % of the water and then
add the dichromate.
Stir until dissolution is complete and then add the remaining water.
e) Method 5:
 For the maximum environmental performance of the bonded joint, the etched surface, prepared in
accordance with method 4, is further treated by anodizing prior to bonding.
7.2.1.2 Aluminium and alloys (anodized)
7.2.1.2.1 General
Unsealed chromic and sulfuric acid anodized surfaces are suitable for general-purpose bonding when the only
preparation normally required is de-greasing followed by light abrasion (see 5.2.2 and 6.1.1). Of the two, the
chrome-based process is considered the better, and for critical work, such as aircraft and associated
construction, it shall be implemented as outlined in 7.2.1.2.2.
By contrast, surfaces which have been “hard”-anodized shall not be bonded because the surface oxide is
unsuitable for bonding and has to be removed — preferably by blasting (see 5.2.2 and 6.1.2). Following this,
any of the methods (1 to 5 inclusive) given in 7.2.1.1 above can be used.
For general-purpose work, preparation is normally limited to de-greasing and light abrasion (see 5.2.2 and
6.1.1). However, surfaces shall be bonded as quickly as possible after anodizing and preferably within 4 h. For
critical structural applications, the oxide shall be removed by blasting (see 5.2.2 and 6.1.2). Following this, the
fresh surface can be etched as described above, or etched and re-anodized, prior to bonding.
7.2.1.2.2 Method
 Remove oil or grease contamination (see 5.2.2).
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 Scarify by abrading or blasting with alumina grit (see 6.1.1 and 6.1.2).
 Immerse the item to be etched for (20 ± 5) min at (62 ± 2) °C in the etch solution (7.2.1.2.3). Immerse the
item in the electrolyte (7.2.1.2.4) of an anodizing bath set at a temperature of (90 ± 2) °C. Progressively
raise the voltage stepwise to 40 V, in increments not greater than 5 V, over a period of 10 min. Maintain
this voltage for 20 min. Then raise the voltage progressively to 50 V over the next 5 min. Maintain the
voltage at 50 V for a further 5 min.
 Remove the item, wash with tap water and rinse thoroughly in cold distilled or de-ionized water.
 Conduct the “water-break” test.
 Drain for 15 min.
 Dry with warm, dry air for about 10 min at a temperature not exceeding 60 °C.
 Bond as soon as possible after drying and preferably within 4 h. Alternatively, coat the surface with an
adhesive-compatible primer — consult the adhesive manufacturer.
7.2.1.2.3 Etch solution
Before commencing, see Clause 4 and requirements a) to e) of 6.3.2.
The composition of the etch solution is as follows:
Table 4 — Composition of the etch solution for aluminium and alloys (anodized)
Reagent (technical or reagent grade)
Parts by mass (±±±± 1 %)
Potassium dichromate or sodium dichromate 1,0
5,5
Concentrated sulfuric acid (ρ = 1,84 g/ml)
Distilled/de-ionized water 21,5

Prepare the solution as follows: with constant stirring, cautiously add the acid to 60 % of the water and then
add the dichromate.
Stir until dissolution is complete and then add the remaining water.
7.2.1.2.4 Electrolyte
Before commencing, see Clause 4 and requirements a) to e) of 6.3.2.
The initial electrolyte has the proportion of 50 g of chromium trioxide made up into a 1 litre solution with water.
As the chrome content is consumed during the anodizing process, its concentration is maintained by the
addition of more chromium trioxide. The solution strength shall be maintained at between 30 g and 100 g of
chromium trioxide per litre of solution.
7.2.1.3 Chrome plate (irrespective of base material)
7.2.1.3.1 Method
 Remove oil or grease contamination (see 5.2.2).
 Either scarify (see 6.1) and bond (see below) or immerse the item for 1 min to 5 min at (93 ± 2) °C in the
etch solution (7.2.1.3.2).
 Remove the item and rinse thoroughly in cold distilled or de-ionized water.
 Dry in a warm, dry air stream for about 10 min at a temperature not exceeding 65 °C.
 Bond as soon as possible after drying and preferably within 4 h.
7.2.1.3.2 Etch solution
Before commencing, see Clause 4 and requirements a) to e) of 6.3.2.
The composition of the etch solution is as follows:
Table 5 — Composition of the etch solution for chrome plate
Reagent (technical or reagent grade)
Parts by mass (±±±± 1 %)
1,0
Concentrated hydrochloric acid (ρ = 1,18 g/ml)
Distilled/de-ionized water 1,0

Prepare the solution as follows: with constant stirring, cautiously add the acid to the water.
7.2.1.4 Copper and copper alloys (includes brass and bronze)
7.2.1.4.1 Method
 Remove oil or grease contamination (see 5.2.2).
 Either scarify with an alumina-based grit (6.1) and bond (below) or immerse the item at room temperature
for the appropriate, specified time in the preferred of the three etch solutions (7.2.1.4.2). Note that, for
certain alloys, it could be necessary to vary the time required.
 Remove the item and rinse thoroughly in cold distilled or de-ionized water.
 Dry using clean, cold, pressurized air. Hot air will discolour the surface.
 Bond as soon as possible after drying and preferably within 4 h.
7.2.1.4.2 Etch solutions
Before commencing, see Clause 4 and requirements a) to e) of 6.3.2.
a) Ammonium persulfate
The composition is as follows:
Table 6 — Composition of etch solution a) for copper and copper alloys
Reagent (technical or reagent grade)
Parts by mass (±±±± 1 %)
Ammonium persulfate 1,0
Water 3,0
Prepare the solution as follows: with constant stirring, dissolve the ammonium persulfate in the water.
Immerse the parts for 1 min.
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b) Iron(III) chloride
The composition is
...