ASTM D3933-98
(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)
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 This standard does not purport to address all of the safety problems, 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: D 3933 – 98
Standard Guide for
Preparation of Aluminum Surfaces for Structural Adhesives
Bonding (Phosphoric Acid Anodizing)
This standard is issued under the fixed designation D 3933; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope 4. Significance and Use
1.1 This guide describes the requirements for phosphoric 4.1 Durable adhesive bonds between metal to metal, metal
acid anodizing of aluminum and its alloys for structural to composites can be obtained reliably only through proper
adhesive bonding. selection and careful control of the materials used and the steps
1.2 The procedure included herein is based on the commer- in the bonding process. The preparation of the metallic
cial practice of numerous agencies and organizations. The substrates to obtain surfaces with appropriate characteristics is
method may be revised or supplemented, as necessary, to a critical step. Improper surface preparation can produce
include methods based on proven performance. seemingly acceptable bonds that can degrade rapidly with time.
1.3 The surface preparation of metal systems used for This guide describes one method on how to properly prepare
qualification and quality-control testing of the adhesive should aluminum surfaces can be obtained.
be agreed upon between the manufacturer and the user. 4.2 The formation of reproducible, durable, adhesive bonds
1.4 The values stated in SI units are to be regarded as the in structural assemblies requires great care in the selection of
standard. The values given in parentheses are for information materials, the preparation of the surfaces of the components to
only. be bonded, the fit of the components, and the performance of
1.5 This standard does not purport to address all of the the steps in the bonding process. Experience has shown that
safety concerns, if any, associated with its use. It is the when adhesively bonded aluminum surfaces which have been
responsibility of the user of this standard to establish appro- prepared in accordance with this guide produce relatively
priate safety and health practices and determine the applica- reproducible, durable bonds.
bility of regulatory limitations prior to use. A specific precau-
5. Apparatus
tion is given in 5.5.
5.1 Locate surface preparation and drying facilities separate
2. Referenced Documents
from other activities or equipment, or both, to preclude
2.1 ASTM Standards: contamination by substances detrimental to adhesion.
D 907 Terminology of Adhesives 5.2 Facilities should be arranged such that parts can flow
D 2651 Guide for Preparation of Metal Surfaces for Adhe- from the beginning of surface preparation to the priming
sive Bonding operation without being touched.
2.2 Federal Specifications: 5.3 Filters or traps, or both, should be installed for removing
0-0-670 Orthophosphoric Acid, Technical airborne dust, moisture, and oil from all air lines or ducts used
for solution agitation and parts drying. Periodically check,
3. Terminology
clean, or replace filters to ensure proper operation.
3.1 Definitions—Many terms in this guide are defined in
5.4 Surface preparation facilities should not be used for
Terminology D 907. purposes other than the preparation of parts for adhesive
bonding and subsequent finishing.
5.5 Equipment requirements for this process include equip-
This guide is under the jurisdiction of ASTM Committee D-14 on Adhesives
ment normally used in the chemical processing of aluminum
and is the direct responsibility of Subcommittee D14.80 on Metal Bonding
alloys, with the following special provisions:
Adhesives.
Current edition approved May 10, 1998. Published March 1999. Originally
published as D3933–80. Last previous edition D3933–93.
Annual Book of ASTM Standards, Vol 15.06.
Available from the Superintendent of Documents, U.S. Government Printing
Office, Washington, DC 20403.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 3933
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.
ductive material that anodizes, that is, aluminum or titanium in
NOTE 2—Caution: Solutions used in this process are corrosive and
the form of wire, hooks, springs, clips, etc.
toxic. Avoid breathing solution mists or vapors. Do not allow solutions to
5.5.3 The phosphoric acid anodizing tank lining shall be of
get on the eyes, on the skin, or on 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
6.7 Parts must be water-break-free following rinsing after
system for mixing the tank contents.
alkaline cleaning, after deoxidizing, and after anodizing.
5.5.4 Terminals for electrical current shall be designed and
positioned such that parts cannot be “burned.”
7. Procedure
5.5.5 The electrical system used during a single-rack anodic
7.1 Perform the surface preparation process in a continuous
process shall be adequate for producing 10-V dc and maintain-
operation as detailed in the flow chart, Fig. 1.
ing any set voltage within 61-V dc.
7.2 Complete all fabrication processes, inspections, prefit,
5.5.6 The electrical system used during a multiple-rack
etc. before the start of the preparation cycle.
process shall be adequate for producing 15-V dc and maintain-
7.3 Complete all “hand work” before solvent cleaning.
ing any set voltage within 61-V dc.
7.4 Once racked for alkaline cleaning, parts shall not be
5.5.7 Rinse tanks should be placed adjacent to processing
touched by anything except the applicable processing solution
tanks in such a manner that parts can be easily and quickly
and rinse waters, until the parts are dried after primer applica-
moved from one solution to another so that the parts will not
tion (5.2).
become dry during successive steps of the process.
7.5 The “wet” processing steps, from alkaline cleaning
5.5.8 Incoming solution makeup water and rinse water shall
through drying after phosphoric acid anodizing, should be
contain not more than the “recommended upper limit” for
performed in one continuous uninterrupted sequence of pro-
fluoride and not more than the “highest desirable level” of
cesses, with the parts not drying at any time until the oven
dissolved chemicals based on American Chemical Society
drying after the rinse following phosphoric acid anodizing.
standards for deionized or distilled water, or both (1.7 ppm
7.5.1 Should the parts become delayed prior to anodizing
fluoride, 500 ppm total dissolved solids, etc.) except that:
during this wet processing, hold the parts in the applicable
5.5.8.1 Chloride shall not exceed 25 ppm.
rinse tank.
5.5.8.2 pH shall be between 5.5 and 8.0.
7.5.2 There shall be no holding of parts in the processing
sequencing after anodizing.
NOTE 1—Most regionally distributed potable water will meet these
requirements. 7.6 Should the electric current fail or otherwise be inter-
rupted during the phosphoric acid anodizing, anodizing may be
5.5.8.3 If the above requirements cannot be met, the incom-
continued for an additional 20 to 25 min, if the potential can be
ing water shall be deionized and maintained within the
reestablished within 2 min. If the potential cannot be reestab-
following limits:
lished within 2 min, then rinse and reprocess starting with the
(a) Total dissolved solids shall not exceed 150 ppm.
deoxidizer.
(b) pH shall be between 5.5 and 8.0.
7.7 Apply adhesive primer within 72 h after oven drying
following the phosphoric acid anodizing. Parts should be held
6. Manufacturing
in a limited contamination area prior to priming and should not
6.1 Parts shall be racked or suspended from frames such that
be handled (5.2). However, it is most desirable to prime parts
they all have firm, reliable electrical contact with the anode
as soon as possible to minimize the possibility of inadvertent
connections, so that the parts do not contact each other and that
contamination.
rinse water contacts all surfaces and drains freely.
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