ASTM D2651-01(2016)
(Guide)Standard Guide for Preparation of Metal Surfaces for Adhesive Bonding
Standard Guide for Preparation of Metal Surfaces for Adhesive Bonding
ABSTRACT
This guide covers procedures for preparing various wrought metal surfaces for adhesive bonding. Surface treatment methods involving both mechanical and chemical techniques are included for aluminum alloys, stainless steel, carbon steel, titanium alloys, magnesium alloys, and copper and copper alloys. For aluminum alloys: vapor or non-etching alkaline degreasing; sulfuric acid-sodium dichromate or sulfuric acid-ferric sulfate solution etching; phosphoric and sulfuric acid anodizing; propriety cleaning; secondary bonding; brush plate bond etching; mechanical abrasion; electrochemical cleaning; and anodic etching may be used. For stainless steel: mechanical methods such as wire brushing, rubbing with metal wool, hand sanding, and dry sand, grit, or vapor blast honing; etching using sulfuric-nitric-hydrofluoric, hydrochloric-orthosphosphoric-hydrofluoric, sulfuric-sodium dichromate, sodium metasilicate, and hydrochloric-sulfuric-dichromate acid solutions; and vigorous scouring with wet cloth and commercial household cleaner may be used. Same mechanical methods as that employed in stainless steel and chemical etching by nitric-phosphoric acid solution may be used for carbon steel preparation. For titanium alloys: mechanical abrasion; hydrochloric-orthophosphoric-hydrofluoric acid solution etching; and chromic acid or fluoride anodizing may be used. Surface preparation for magnesium alloys which is closely associated with corrosion prevention shall involve vapor, alkaline-detergent solution, chromic acid, and sodium hydroxide acid degreasing; anodic treatment; and the use of conversion coatings and wash primers. Nitric acid-ferric chloride solution degreasing; sulfuric acid-dichromate-ferric sulfate solution etching; and chemical treatment by nitric-acid-sodium chlorite solutions may be used for copper and copper alloy preparation.
SCOPE
1.1 This guide covers procedures that have proved satisfactory for preparing various wrought metal surfaces for adhesive bonding. It does not address the preparation of cast metals.
1.2 Surface preparation methods are included for:
Metal
Section
Aluminum Alloys
7
Stainless Steel
8
Carbon Steel
9
Titanium Alloys
10
Magnesium Alloys
Copper and Copper Alloys
11
12
1.3 Procedures included herein are based on the commercial practice of numerous agencies and organizations. The methods may be revised or supplemented, as necessary, to include methods based on proven performance.
1.4 The surface preparation of metal systems used for qualification and quality control testing of the adhesive should be agreed upon by both manufacturer and user.
1.5 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D2651 − 01 (Reapproved 2016)
Standard Guide for
Preparation of Metal Surfaces for Adhesive Bonding
This standard is issued under the fixed designation D2651; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
INTRODUCTION
It is impossible and impractical to present a single surface-preparation method for a metal group,
such as aluminum alloys, stainless steels, magnesium alloys, etc.The wide variety of individual alloys
and heat treatments under each group, the fact that certain adhesives exhibit specific compatibilities
with surface preparation and the complexity and nature of parts being bonded preclude the use of an
all-inclusive procedure for a metal group. Procedures for aluminum alloys are well standardized,
possiblybecausemorebondinghasbeendonewiththesealloys.Preliminarytestsshouldbeconducted
with the specific adhesive and the exact lot of metals to determine performance.This is especially true
for stainless steel. The adhesive manufacturers’ recommendation should also be considered.
1. Scope responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica-
1.1 This guide covers procedures that have proved satisfac-
bility of regulatory limitations prior to use.
tory for preparing various wrought metal surfaces for adhesive
bonding. It does not address the preparation of cast metals.
2. Referenced Documents
1.2 Surface preparation methods are included for:
2.1 ASTM Standards:
Metal Section
D907 Terminology of Adhesives
Aluminum Alloys 7
D1125 Test Methods for Electrical Conductivity and Resis-
Stainless Steel 8
Carbon Steel 9
tivity of Water
Titanium Alloys 10
D2674 Methods ofAnalysis of Sulfochromate Etch Solution
Magnesium Alloys 11
Used in Surface Preparation of Aluminum
Copper and Copper Alloys 12
D3933 Guide for Preparation of Aluminum Surfaces for
1.3 Proceduresincludedhereinarebasedonthecommercial
Structural Adhesives Bonding (Phosphoric Acid Anodiz-
practice of numerous agencies and organizations. The methods
ing)
may be revised or supplemented, as necessary, to include
2.2 ASM International Document:
methods based on proven performance.
Metals Handbook Volume V
1.4 The surface preparation of metal systems used for
2.3 Military Specifications:
qualification and quality control testing of the adhesive should
MIL-A-8625 Type II, Anodic Coatings for Aluminum and
be agreed upon by both manufacturer and user.
Aluminum Alloys
1.5 The values stated in SI units are to be regarded as the
MIL-M-3171 Magnesium Alloy, Processes for Pretreatment
standard. The values given in parentheses are for information
and Prevention of Corrosion
only.
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
ThisguideisunderthejurisdictionofASTMCommitteeD14onAdhesivesand the ASTM website.
is the direct responsibility of Subcommittee D14.80 on Metal Bonding Adhesives. Available from American Society of Metals (ASM International), 9639 Kins-
Current edition approved May 1, 2016. Published May 2016. Originally man Rd., Materials Park, OH 44073-0002, http://www.asminternational.org.
approved in 1967. Last previous edition approved in 2008 as D2651 – 01 (2008). Available from DLA Document Services, Building 4/D, 700 Robbins Ave.,
DOI: 10.1520/D2651-01R16. Philadelphia, PA 19111-5094, http://quicksearch.dla.mil.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D2651 − 01 (2016)
MIL-M-45202 Magnesium Alloy, Anodic Treatment of periodically and analyzed for materials pertinent to the particu-
lar treatment method, such as, titration for hexavalent chro-
2.4 SAE Standards:
mium (CrO ), iron, chlorides, aluminum, etc. A pH reading or
Aerospace Material Specification 2470 E Anodic Treatment
acid content of trichloroethane vapor degreasing solution, or
of Aluminum Base Alloy, Chromic Acid Treatment
both, should be obtained. Standards should be established and
3. Terminology
records kept for such tests on each lot or vat of solution.
Recordsshouldindicatethecontinuousconditionsofsolutions,
3.1 Definitions—Many of the terms in this guide are defined
such as amount of constituents added to bring solutions within
in Terminology D907.
limits, amount of contaminants present and date prepared (see
4. Apparatus Methods D2674).
4.1 Trays or Pans, suitable for preparation of laboratory 5.4 Room Conditions for surface preparation as well as
specimens and small parts. Generally in production, a series of other adhesive bonding operations should be controlled for
tanks containing the necessary solutions is arranged with temperatures of 18 to 24°C (65 to 75°F), relative humidity of
overhead cranes to transport parts to be prepared.Tanks should 40 to 65 %, air-filtered to remove dust and pressure maintained
be lined with suitable materials to resist the solutions, and at slightly higher than ambient.
methodsforcirculatingthesolutionsandheatingwithtempera- 5.4.1 The time and conditions between surface preparation
ture controls should be included if required. and applying adhesive primer, if used, and bonding are critical.
Usually, the time should not exceed 8 h and parts should be
4.2 Hooks, Baskets, Clamps, or other holding devices, may
covered or wrapped in Kraft paper. Prepared surfaces can
beusedtoconveypartsbeingprepared.Theuseofa300Series
change their characteristics on standing and adhesives vary
stainless steel for such equipment is suggested. Other metals
widely in their tolerance of adherend surface conditions. In
may be used if they are resistant to the solution used.
production bonding of complicated or large parts, the time
interval may exceed 8 h. Investigation should be made to
5. Conditions
determine the time limitation of the adhesive and the rate of
5.1 Handling—All parts during and after processing and
change on the surface of the adherend. On the basis of the
before bonding should be handled as little as possible and only
results of such an investigation, it may be possible to extend
with clean, lint-free cotton or nylon fabric gloves.
the length of time and establish standards for the interval
5.2 Water used for preparing solutions should be distilled,
between surface preparation and adhesive application to fit
steam condensate, demineralized, deionized or otherwise
production schedules. Contaminating operations in the area
treated, if necessary, to obtain a condition of not more than 50
should be avoided. Especially detrimental are paint or other
ppm of solids and have a pH between 5.5 and 10, or not more
spraying operations, processes using powdered materials, oil
than 50 ppm of dissolved solids and not over 30 micromhs
vapors from pumps and other machinery and spraying of mold
conductance (see Test Methods D1125). Rinsing may be done
release agents.
bysprayorbydippinginatankinwhichthewateriscirculated
5.5 Common Steps:
and constantly being renewed by an overflow method. After
5.5.1 Remove ink markings or stamped identifications from
removing from any rinse the water-break test is commonly
the metals. This can be accomplished by wiping with a cloth
used. If the water film is discontinuous, it indicates that the
wetted with a variety of commercial solvents, such as acetone,
process is unsatisfactory and must be repeated (see 5.5.4).
methyl ethyl ketone, lacquer thinner and naphtha.
Other methods, such as indicator paper and contact angle, have
5.5.2 The preferred degreasing method is vapor degreasing
been used to determine the effectiveness of the process.
with 1,1,1-trichloroethane. Commercial vapor degreasing
Rinsing should be sufficiently long and vigorous to assure
equipment is usually used. This equipment has a deep tank
removal of soluble residue chemicals, or particles. Critical
with provision for heating a chlorinated solvent to 82 to 87°C
specific temperatures are specified for the rinse water in some
(180 to 190°F). Parts are suspended in the vapor zone above
processes. Where not specified, temperature is not critical. The
the hot liquid and allowed to remain until there is condensation
number of times a process may be repeated depends upon the
and run off (approximately 5 min). This step is repeated if
amount of metal removed in relation to the tolerance require-
necessary until all visible contamination is removed. The parts
ments for the part and whether clad or bare metal is used.
are raised above the tank and allowed to dry thoroughly.
Generally, not more than two repeat treatments are permitted.
Previously bonded parts, such as honeycomb core materials,
NOTE 1—No entirely foolproof method exists to determine bondability
are usually not degreased due to difficulty in removing residue.
of a metal surface after preparation.Trial bonding followed by testing and
5.5.3 Following vapor degreasing, mechanical or chemical
evaluation against mechanical strength standards should be conducted to
cleaning methods are usually employed.
determine initial and continuous effectiveness of a method.
5.5.4 A water-break test is a common method used to
5.3 Solutions—The life of solutions should be standardized.
analyze surface cleanliness. This test depends on the observa-
The useful life of solutions depends upon the number and size
tion that a clean surface (one that is chemically active or polar)
of the parts being prepared. Solutions should be sampled
will hold a continuous film of water, rather than a series of
isolated droplets. This is known as a water-break-free condi-
tion. A break in the water film indicates a soiled or contami-
Available from Society of Automotive Engineers (SAE), 400 Commonwealth
Dr., Warrendale, PA 15096-0001, http://www.sae.org. nated area. Distilled water should be used in the test, and a
D2651 − 01 (2016)
drainage time of about 30 s should be allowed. Any trace of 7.4.4 Sulfuric Acid Anodizing—Amethod found suitable for
residual cleaning solution should be removed or a false bare aluminum (nonclad), machined, or chemically milled
conclusion may be made. If a water-break-free condition is not parts which must be corrosion protected is to anodize with
observed on the treated surface, it should not be used for sulfuric acid. Do not seal the anodized parts with boiling water
bonding. The surface should be recleaned until the test is before bonding. Do not allow the time interval between
passed. If continuous failures occur, the treating process itself treatment and bonding to exceed 72 h, and cover or wrap all
should be analyzed to determine the cause of the problem. parts during the interval with a non-contaminating vapor
barrier material.
6. Report
NOTE 2—Details of the process are contained in Specification AMS
6.1 Thereportforallmethodsconsistsofflowcharts,record
2470 E or Military Specification MIL-A-8625.
sheets or other methods that indicate all steps in the surface
7.4.5 Proprietary Cleaners—Some proprietary, commer-
preparation used, with spaces for entries made upon comple-
cially available metal surface preparations have been found
tion of each step.
suitable for preparing the surfaces for adhesive bonding.
ALUMINUM ALLOYS Full-scale property tests should be run with the metal surfaces
so prepared with the adhesive in question before accepting the
7. Procedure
process.
7.1 Aluminum alloys may be pretreated with many different
7.4.6 Secondary Bonding—When secondary bonding
methods, using both acidic and basic cleaners.
(bonding of parts that contain previously bonded areas) or
repair of a disbonded assembly in service is necessary, it is
7.2 A typical pretreatment would normally involve the
usually impossible and undesirable to immerse these parts in
following steps:
surface-preparation solutions without destroying or harming
7.2.1 Vapor degrease or non-etching alkaline cleaner,
the original adhesive bond. Satisfactory surface preparations
7.2.2 Rinse,
have been accomplished by using paste-type etchants. These
7.2.3 Acid or alkaline, and
paste systems can be made by adding fumed silica to the
7.2.4 Rinse.
sulfuric-dichromic acid solutions. The application of these
7.3 After 7.2.4, the parts may be dried or they may be given
pastesystemsallowsfortheiruseinfairlycontrolledareas.The
an anodizing treatment.
etching time is generally 10 to 20 min. Exercise extreme care
7.4 Typical pretreatments are listed in 7.4.1. Refer to the to ensure removal of all traces of the etchant. A thorough
appropriate literature for details on cleaning techniques and rinsing with distilled water may be necessary to ensure
procedures. complete removal. Several commercial products are available.
7.4.1 Alkaline degreasing solutions may be used instead of, Somecommercialcompoundsundertheclassificationof“wash
or in addition to, vapor degreasing. Commercially available primers” have been found to perform satisfactorily in place of
proprietary solutions may be used. A common degreasing the paste type systems. Bond strengths obtained using either of
method is to immerse for 10 min at 70 to 82°C (160 to 180°F)
these surface preparations are somewhat lower than those from
in the following solution by weight: 3.0 parts sodium the immersion processes.
metasilicate, 1.5 parts sodium hydroxide, 0.5 parts sodium
7.4.7 Brush Plate Bond Etch (Stylus Method):
dodecylbenzene sulfonate, such as Nacconol 90G , to 133.0
7.4.7.1 General—This method of electrochemical surface
parts water.
preparation, although not widely known, has been effectively
7.4.2 Acid etching solutions typically used are the follow-
demonstrated for small batch runs where tanks and other
ing:
capital-intensive methods might have been used.Almost all of
7.4.2.1 Sulfuric Acid/Sodium Dichromate (optimized FPL
thesolutions,“brushes”(orstyli),andelectricalpowersupplies
etch).
are proprietary. When this method is used, the entire “family”
Material Concentration
of proprietary items should be used; mixed usage of items
Sulfuric Acid (66°Be or Baume) 38 to 41.5 oz/gal (287.9 to 310.0 g/L)
betw
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