ASTM D3933-98(2010)
(Guide)Standard Guide for Preparation of Aluminum Surfaces for Structural Adhesives Bonding (Phosphoric Acid Anodizing)
Standard Guide for Preparation of Aluminum Surfaces for Structural Adhesives Bonding (Phosphoric Acid Anodizing)
SIGNIFICANCE AND USE
Durable adhesive bonds between metal to metal, metal to composites can be obtained reliably only through proper selection and careful control of the materials used and the steps in the bonding process. The preparation of the metallic substrates to obtain surfaces with appropriate characteristics is a critical step. Improper surface preparation can produce seemingly acceptable bonds that can degrade rapidly with time. This guide describes one method on how to properly prepare aluminum surfaces can be obtained.
The formation of reproducible, durable, adhesive bonds in structural assemblies requires great care in the selection of materials, the preparation of the surfaces of the components to be bonded, the fit of the components, and the performance of the steps in the bonding process. Experience has shown that when adhesively bonded aluminum surfaces which have been prepared in accordance with this guide produce relatively reproducible, durable bonds.
SCOPE
1.1 This guide describes the requirements for phosphoric acid anodizing of aluminum and its alloys for structural adhesive bonding.
1.2 The procedure included herein is based on the commercial practice of numerous agencies and organizations. The method may be revised or supplemented, as necessary, to include methods based on proven performance.
1.3 The surface preparation of metal systems used for qualification and quality-control testing of the adhesive should be agreed upon between the manufacturer and the user.
1.4 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.
1.5 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. A specific precaution is given in 5.5.
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: D3933 − 98 (Reapproved 2010)
Standard Guide for
Preparation of Aluminum Surfaces for Structural Adhesives
Bonding (Phosphoric Acid Anodizing)
This standard is issued under the fixed designation D3933; 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.
1. Scope 3. Terminology
1.1 This guide describes the requirements for phosphoric 3.1 Definitions—Many terms in this guide are defined in
Terminology D907.
acid anodizing of aluminum and its alloys for structural
adhesive bonding.
4. Significance and Use
1.2 The procedure included herein is based on the commer-
4.1 Durable adhesive bonds between metal to metal, metal
cial practice of numerous agencies and organizations. The
to composites can be obtained reliably only through proper
method may be revised or supplemented, as necessary, to
selectionandcarefulcontrolofthematerialsusedandthesteps
include methods based on proven performance.
in the bonding process. The preparation of the metallic
1.3 The surface preparation of metal systems used for
substrates to obtain surfaces with appropriate characteristics is
qualification and quality-control testing of the adhesive should
a critical step. Improper surface preparation can produce
be agreed upon between the manufacturer and the user.
seeminglyacceptablebondsthatcandegraderapidlywithtime.
1.4 The values stated in SI units are to be regarded as the This guide describes one method on how to properly prepare
standard. The values given in parentheses are for information aluminum surfaces can be obtained.
only.
4.2 The formation of reproducible, durable, adhesive bonds
1.5 This standard does not purport to address all of the in structural assemblies requires great care in the selection of
safety concerns, if any, associated with its use. It is the materials, the preparation of the surfaces of the components to
responsibility of the user of this standard to establish appro- be bonded, the fit of the components, and the performance of
priate safety and health practices and determine the applica- the steps in the bonding process. Experience has shown that
bility of regulatory limitations prior to use. A specific precau- when adhesively bonded aluminum surfaces which have been
tion is given in 5.5. prepared in accordance with this guide produce relatively
reproducible, durable bonds.
2. Referenced Documents
5. Apparatus
2.1 ASTM Standards:
5.1 Locate surface preparation and drying facilities separate
D907 Terminology of Adhesives
from other activities or equipment, or both, to preclude
D2651 GuideforPreparationofMetalSurfacesforAdhesive
contamination by substances detrimental to adhesion.
Bonding
5.2 Facilities should be arranged such that parts can flow
2.2 Federal Specifications:
from the beginning of surface preparation to the priming
0-0-670 Orthophosphoric Acid, Technical
operation without being touched.
5.3 Filtersortraps,orboth,shouldbeinstalledforremoving
airborne dust, moisture, and oil from all air lines or ducts used
ThisguideisunderthejurisdictionofASTMCommitteeD14onAdhesivesand
is the direct responsibility of Subcommittee D14.80 on Metal Bonding Adhesives.
for solution agitation and parts drying. Periodically check,
Current edition approved Oct. 1, 2010. Published October 2010. Originally
clean, or replace filters to ensure proper operation.
approved in 1980. Last previous edition approved in 2004 as D3933 – 98 (2004).
DOI: 10.1520/D3933-98R10.
5.4 Surface preparation facilities should not be used for
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
purposes other than the preparation of parts for adhesive
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
bonding and subsequent finishing.
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
5.5 Equipment requirements for this process include equip-
AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,
ment normally used in the chemical processing of aluminum
732 N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401, http://
www.access.gpo.gov. alloys, with the following special provisions:
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D3933 − 98 (2010)
5.5.1 Racks and frames that are electrically anodic shall be 6.4 If parts become contaminated, either prior to or subse-
constructed of materials that will not cause corrosive reactions quent to anodizing, corrective action shall be accomplished by
with the suspension wires or clips, or the parts, during the reprocessing, beginning with alkaline cleaning.
entire process. “Picture-frame”-type racks have performed
6.5 To ensure solution homogeneity, agitate immediately
satisfactorily.
prior to process use and after every addition of water or
5.5.2 Parts shall be attached to racks or frames with con-
chemicals. (Warning—Solutions used in this process are
ductive material that anodizes, that is, aluminum or titanium in
corrosive and toxic. Avoid breathing solution mists or vapors.
the form of wire, hooks, springs, clips, etc.
Do not allow solutions to get on the eyes, on the skin, or on
5.5.3 The phosphoric acid anodizing tank lining shall be of
clothing.)
such material that interaction between the solutions, parts,
6.5.1 Consult Industrial Hygiene for safety precautions.
frames, racks, or clips and hangers does not interfere with the
6.6 Control the time interval between withdrawal from
anodic process and is suitable for use as a cathode. Tanks
processing solutions and rinsing so that there is no drying of
should be equipped with a surface skimming device to remove
the solution on the details.
surface contamination, a filtering system, and an agitation
system for mixing the tank contents.
6.7 Parts must be water-break-free following rinsing after
5.5.4 Terminals for electrical current shall be designed and
alkaline cleaning, after deoxidizing, and after anodizing.
positioned such that parts cannot be “burned.”
5.5.5 The electrical system used during a single-rack anodic
7. Procedure
process shall be adequate for producing 10-V dc and maintain-
7.1 Perform the surface preparation process in a continuous
ing any set voltage within 61-V dc.
operation as detailed in the flow chart, Fig. 1.
5.5.6 The electrical system used during a multiple-rack
process shall be adequate for producing 15-V dc and maintain-
7.2 Complete all fabrication processes, inspections, prefit,
ing any set voltage within 61-V dc. etc. before the start of the preparation cycle.
5.5.7 Rinse tanks should be placed adjacent to processing
7.3 Complete all “hand work” before solvent cleaning.
tanks in such a manner that parts can be easily and quickly
7.4 Once racked for alkaline cleaning, parts shall not be
moved from one solution to another so that the parts will not
touched by anything except the applicable processing solution
become dry during successive steps of the process.
and rinse waters, until the parts are dried after primer applica-
5.5.8 Incoming solution makeup water and rinse water shall
tion (5.2).
contain not more than the “recommended upper limit” for
fluoride and not more than the “highest desirable level” of
7.5 The “wet” processing steps, from alkaline cleaning
dissolved chemicals based on American Chemical Society
through drying after phosphoric acid anodizing, should be
standards for deionized or distilled water, or both (1.7 ppm
performed in one continuous uninterrupted sequence of
fluoride, 500 ppm total dissolved solids, etc.) except that:
processes, with the parts not drying at any time until the oven
5.5.8.1 Chloride shall not exceed 25 ppm.
drying after the rinse following phosphoric acid anodizing.
5.5.8.2 pH shall be between 5.5 and 8.0.
7.5.1 Should the parts become delayed prior to anodizing
during this wet processing, hold the parts in the applicable
NOTE 1—Most regionally distributed potable water will meet these
requirements. rinse tank.
7.5.2 There shall be no holding of parts in the processing
5.5.8.3 If the above requirements cannot be met, the incom-
sequencing after anodizing.
ing water shall be deionized and maintained within the
following limits:
7.6 Should the electric current fail or otherwise be inter-
(a) Total dissolved solids shall not exceed 150 ppm.
ruptedduringthephosphoricacidanodizing,anodizingmaybe
(b) pH shall be between 5.5 and 8.0.
continued for an additional 20 to 25 min, if the potential can be
reestablished within 2 min. If the potential cannot be reestab-
6. Manufacturing
lished within 2 min, then rinse and reprocess starting with the
deoxidizer.
6.1 Partsshallberackedorsuspendedfromframessuchthat
they all have firm, reliable electrical contact with the anode
7.7 Apply adhesive primer within 72 h after oven drying
connections,sothatthepartsdonotcontacteachotherandthat
following the phosphoric acid anodizing. Parts should be held
rinse water contacts all surfaces and drains freely.
in a limited contamination area prior to priming and should not
be handled (5.2). However, it is most desirable to prime parts
6.2 Taketheutmostcarethatthepartsarenottouchedatany
as soon as possible to minimize the possibility of inadvertent
time during the entire process, such as touching of adjacent
contamination
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