ASTM D3933-98(2004)
(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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Designation:D3933–98(Reapproved2004)
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
acid anodizing of aluminum and its alloys for structural Terminology D907.
adhesive bonding.
4. Significance and Use
1.2 The procedure included herein is based on the commer-
cial practice of numerous agencies and organizations. The 4.1 Durable adhesive bonds between metal to metal, metal
to composites can be obtained reliably only through proper
method may be revised or supplemented, as necessary, to
include methods based on proven performance. selectionandcarefulcontrolofthematerialsusedandthesteps
in the bonding process. The preparation of the metallic
1.3 The surface preparation of metal systems used for
qualification and quality-control testing of the adhesive should substrates to obtain surfaces with appropriate characteristics is
a critical step. Improper surface preparation can produce
be agreed upon between the manufacturer and the user.
1.4 The values stated in SI units are to be regarded as the seeminglyacceptablebondsthatcandegraderapidlywithtime.
This guide describes one method on how to properly prepare
standard. The values given in parentheses are for information
only. aluminum surfaces can be obtained.
4.2 The formation of reproducible, durable, adhesive bonds
1.5 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the in structural assemblies requires great care in the selection of
materials, the preparation of the surfaces of the components to
responsibility of the user of this standard to establish appro-
priate safety and health practices and determine the applica- be bonded, the fit of the components, and the performance of
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
2. Referenced Documents
reproducible, durable bonds.
2.1 ASTM Standards:
5. Apparatus
D907 Terminology of Adhesives
5.1 Locate surface preparation and drying facilities separate
D2651 Guide for Preparation of Metal Surfaces for Adhe-
sive Bonding from other activities or equipment, or both, to preclude
contamination by substances detrimental to adhesion.
2.2 Federal Specifications:
0-0-670 Orthophosphoric Acid, Technical 5.2 Facilities should be arranged such that parts can flow
from the beginning of surface preparation to the priming
operation without being touched.
5.3 Filtersortraps,orboth,shouldbeinstalledforremoving
ThisguideisunderthejurisdictionofASTMCommitteeD14onAdhesivesand
airborne dust, moisture, and oil from all air lines or ducts used
is the direct responsibility of Subcommittee D14.80 on Metal Bonding Adhesives.
Current edition approved April 1, 2004. Published April 2004. Originally for solution agitation and parts drying. Periodically check,
approved in 1980. Last previous edition approved in 1998 as D3933 – 98. DOI:
clean, or replace filters to ensure proper operation.
10.1520/D3933-98R04.
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
Standards volume information, refer to the standard’s Document Summary page on
bonding and subsequent finishing.
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 (2004)
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
corrosive and toxic. Avoid breathing solution mists or vapors.
ductive material that anodizes, that is, aluminum or titanium in
the form of wire, hooks, springs, clips, etc. Do not allow solutions to get on the eyes, on the skin, or on
clothing.)
5.5.3 The phosphoric acid anodizing tank lining shall be of
6.5.1 Consult Industrial Hygiene for safety precautions.
such material that interaction between the solutions, parts,
6.6 Control the time interval between withdrawal from
frames, racks, or clips and hangers does not interfere with the
processing solutions and rinsing so that there is no drying of
anodic process and is suitable for use as a cathode. Tanks
the solution on the details.
should be equipped with a surface skimming device to remove
6.7 Parts must be water-break-free following rinsing after
surface contamination, a filtering system, and an agitation
alkaline cleaning, after deoxidizing, and after anodizing.
system for mixing the tank contents.
5.5.4 Terminals for electrical current shall be designed and
7. Procedure
positioned such that parts cannot be “burned.”
7.1 Perform the surface preparation process in a continuous
5.5.5 The electrical system used during a single-rack anodic
operation as detailed in the flow chart, Fig. 1.
process shall be adequate for producing 10-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.
5.5.6 The electrical system used during a multiple-rack
7.3 Complete all “hand work” before solvent cleaning.
process shall be adequate for producing 15-V dc and maintain-
7.4 Once racked for alkaline cleaning, parts shall not be
ing any set voltage within 61-V dc.
touched by anything except the applicable processing solution
5.5.7 Rinse tanks should be placed adjacent to processing
and rinse waters, until the parts are dried after primer applica-
tanks in such a manner that parts can be easily and quickly
tion (5.2).
moved from one solution to another so that the parts will not
7.5 The “wet” processing steps, from alkaline cleaning
become dry during successive steps of the process.
through drying after phosphoric acid anodizing, should be
5.5.8 Incoming solution makeup water and rinse water shall
performed in one continuous uninterrupted sequence of pro-
contain not more than the “recommended upper limit” for
cesses, with the parts not drying at any time until the oven
fluoride and not more than the “highest desirable level” of
drying after the rinse following phosphoric acid anodizing.
dissolved chemicals based on American Chemical Society
7.5.1 Should the parts become delayed prior to anodizing
standards for deionized or distilled water, or both (1.7 ppm
during this wet processing, hold the parts in the applicable
fluoride, 500 ppm total dissolved solids, etc.) except that:
rinse tank.
5.5.8.1 Chloride shall not exceed 25 ppm.
7.5.2 There shall be no holding of parts in the processing
5.5.8.2 pH shall be between 5.5 and 8.0.
sequencing after anodizing.
7.6 Should the electric current fail or otherwise be inter-
NOTE 1—Most regionally distributed potable water will meet these
requirements. ruptedduringthephosphoricacidanodizing,anodizingmaybe
continued for an additional 20 to 25 min, if the potential can be
5.5.8.3 If the above requirements cannot be met, the incom-
reestablished within 2 min. If the potential cannot be reestab-
ing water shall be deionized and maintained within the
lished within 2 min, then rinse and reprocess starting with the
following limits:
deoxidizer.
(a) Total dissolved solids shall not exceed 150 ppm.
7.7 Apply adhesive primer within 72 h after oven drying
(b) pH shall be between 5.5 and 8.0.
following the phosphoric acid anodizing. Parts should be held
in a limited contamination area prior to priming and should not
6. Manufacturing
be handled (5.2). However, it is most desirable to prime parts
6.1 Partsshallberackedorsuspendedfromframessuchthat
as soon as possible to minimize the possibility of inadvertent
they all have firm, reliable electrical contact with the anode
contamination.
connections,sothatthepartsdonotcontacteachotherandthat
7.8 Rinse Requirements:
rinse water contacts all surfaces and drains freely.
7.8.1 Rinsing may be by spray or immersion. Single
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