ASTM B253-11(2022)

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: B253 − 11 (Reapproved 2022)
Standard Guide for
Preparation of Aluminum Alloys for Electroplating
This standard is issued under the fixed designation B253; 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.
1. Scope ization established in the Decision on Principles for the
Development of International Standards, Guides and Recom-
1.1 This guide covers cleaning and conditioning treatments
mendations issued by the World Trade Organization Technical
used before metal deposition (Section 5), and immersion
Barriers to Trade (TBT) Committee.
deposit/strike procedures (Section 6) that enhance the adhesion
of metals that are subsequently applied to aluminum products
2. Referenced Documents
by electrodeposition or by autocatalytic chemical reduction.
2.1 ASTM Standards:
1.2 The following immersion deposit/strike procedures are
B85 Specification for Aluminum-Alloy Die Castings
covered:
B179 Specification for Aluminum Alloys in Ingot and Mol-
1.2.1 Zinc immersion with optional copper strike (6.3).
ten Forms for Castings from All Casting Processes
1.2.2 Zinc immersion with neutral nickel strike (6.4).
B209/B209M Specification for Aluminum and Aluminum-
1.2.3 Zinc immersion with acetate-buffered, nickel glyco-
Alloy Sheet and Plate
late strike (6.5).
B221 Specification forAluminum andAluminum-Alloy Ex-
1.2.4 Zinc immersion with acid or alkaline electroless
truded Bars, Rods, Wire, Profiles, and Tubes
nickel strike.
B221M Specification for Aluminum and Aluminum-Alloy
1.2.5 Tin immersion with bronze strike (6.6).
Extruded Bars, Rods, Wire, Profiles, and Tubes (Metric)
1.3 From the processing point of view, these procedures are
B322 Guide for Cleaning Metals Prior to Electroplating
expected to give deposits on aluminum alloys that are approxi- B432 Specification for Copper and CopperAlloy Clad Steel
mately equivalent with respect to adherence. Corrosion perfor-
Plate
mance is affected by many factors, however, including the E527 Practice for Numbering Metals and Alloys in the
procedure used to prepare the aluminum alloy for electroplat-
Unified Numbering System (UNS)
ing.
3. Significance and Use
1.4 This guide is intended to aid electroplaters in preparing
3.1 Various metals are deposited on aluminum alloys to
aluminum and its alloys for electroplating.
obtain a decorative or engineering finish. The electroplates
1.5 The values stated in SI units are to be regarded as
applied are usually chromium, nickel, copper, brass, silver, tin,
standard. No other units of measurement are included in this
lead, cadmium, zinc, gold, and combinations of these. Silver,
standard.
tin, or gold is applied to electrical equipment to decrease
1.6 This standard does not purport to address all of the
contact resistance or to improve surface conductivity; brass,
safety concerns, if any, associated with its use. It is the
copper, nickel, or tin for assembly by soft soldering; chromium
responsibility of the user of this standard to establish appro-
to reduce friction and obtain increased resistance to wear; zinc
priate safety, health, and environmental practices and deter-
forthreadedpartswhereorganiclubricantsarenotpermissible;
mine the applicability of regulatory limitations prior to use.
tin or lead is frequently employed to reduce friction on bearing
For specific precautionary statements see Section 7 and Ap-
surfaces. Nickel plus chromium or copper plus nickel plus
pendix X1.
chromium is used in decorative applications. Nickel plus brass
1.7 This international standard was developed in accor-
plus lacquer or copper plus nickel plus brass plus lacquer is
dance with internationally recognized principles on standard-
also used for decorative finishes, sometimes with the brass
oxidized and relieved in various ways.
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
Inorganic Coatings and is the direct responsibility of Subcommittee B08.02 on Pre
Treatment. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved May 1, 2022. Published June 2022. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approvedin1951.Lastpreviouseditionapprovedin2017asB253 – 11(2017).DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/B0253-11R22. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B253 − 11 (2022)
3.1.1 Electroless nickel may be applied as a barrier layer hot, aqueous carbonate-phosphate solution (Appendix X1.1).
prior to other deposits, or for engineering purposes. Other types of cleaners are used; for example, mildly alkaline
or acidic soak cleaners are used to remove gross soils. Also
3.2 The preparation of aluminum and aluminum alloy man-
available are a wide range of proprietary cleaners of the
drels for electroforming is described in Practice B432.
“non-etching” type. Some of these are actually buffered
mixtures, similar to the carbonate-phosphate mixture (Appen-
4. Nature of Aluminum and Its Influence on Preparation
dix X1.1) where the so-called non-etching characteristics are
4.1 Microstructure—It is difficult to find a preplating pro-
obtained by buffering the solution to pH levels where the
cedure that is equally satisfactory for all types and tempers of
etching action becomes minimal. Others are truly non-etching
aluminum alloys because the various alloys and products
types where etching is prevented by using silicate inhibitors,
behave differently electrochemically due to their different
such as sodium metasilicate (Na SiO ). These inhibitors al-
2 3
compositions and metallurgical structures. When elements are
ways leave a film of aluminum silicate on the surface. When
added for alloying purposes, they may appear in an aluminum
these materials are used, subsequent deoxidizing solutions
alloy in several different forms: that is, they may be in solid
should contain controlled amounts of fluoride salts to insure
solutioninthealuminumlattice,bepresentasmicroparticlesof
complete removal of the film.
the elements themselves, or be present as particles of interme-
tallic compounds formed by combination with the aluminum.
NOTE 1—General information on the cleaning of metals is given in
Guide B322.
The several solid solution matrices and the 20 or more
microconstituents that may occur in commercial alloys may
5.2 Aftercleaning,aconditioningtreatmentofthesurfaceis
have different chemical reactivities and electropotentials and
generally required. For this to be effective, it must accomplish
their surfaces may not respond uniformly to various chemical
two things: (1) remove the original oxide film and (2) remove
and electrochemical treatments. In addition, the response may
any microconstituents that may interfere with the formation of
be influenced by variations in the microstructure of different
a continuous deposited metallic layer or that may react with
lots of products of the same alloy. In some cases, these
subsequent electroplating solutions.
variations may be introduced or aggravated by preparation
5.2.1 An effective conditioning treatment is immersion of
processes; for example, the heat generated in buffing. The
the work in a warm sodium hydroxide solution (Appendix
electroplater needs to know the aluminum alloy that is to be
X1.3) followed by water rinsing and immersion in a nitric
processed in order to select the best electroplating procedure.
acid-bifluoride desmutting solution (Appendix X1.4).An alter-
In the absence of this information, there are so-called universal
native desmutting solution is sulfuric acid-hydrogen peroxide
procedures that may be used. However these will not neces-
(Appendix X1.5).
sarily be the best or the most economical procedures for the
NOTE 2—When an unmodified sodium hydroxide solution is used,
alloy.
etchingmaybecomenonuniformandheavyconcrete-likescalesmayform
4.2 OxideFilm—In addition to differences in microstructure on tank walls and heating surfaces, their development becoming more
rapid as the concentration of dissolved aluminum increases. The incorpo-
that may affect response to preplating treatments, all aluminum
ration of controlled amounts of deflocculating complexors such as sodium
products have an ever-present natural oxide film. This oxide
gluconate, sodium glucoheptonate, certain sugar derivatives, and certain
film can be removed by various acid and alkaline treatments
substituted sugar amines will eliminate this problem. Many proprietary
and even though it reforms immediately on contact with
etching materials are so modified.
aqueous solutions or air, it then is usually thinner and more
NOTE 3—The universal acid mixture (Appendix X1.9) is applicable to
almost all alloys, and is especially desirable for use with alloys containing
uniform than the original film. The newly formed oxide film
magnesium.
provides a more suitable surface for deposition of the first
metallic layer. 5.2.2 For heat-treated alloys (alloys in a “T” temper), it is
important to remove the relatively thick, heat-treated oxide
5. Cleaning and Conditioning Treatments
film before proceeding with subsequent conditioning treat-
ments.Normally,heat-treatedfilmsareremovedbymachining,
5.1 To obtain consistent results for electroplating on alumi-
num alloys, it is essential that the various cleaning and or by the polishing action on metal surfaces that are buffed.
conditioning treatments provide a surface of uniform activity 5.2.2.1 In the absence of machining or buffing, controlled
for the deposition of the initial metallic layer. First, the surface abrasive blasting may be used to remove this oxide. Fine
should be free of any oil, grease, buffing compound, or other abrasives such as aluminum oxide, ceramic beads, or glass
foreign material. For removing oil, grease, or buffing beads may be used. Silicon carbide abrasives should be
compound, use vapor degreasing, solvent washing, or solvent avoided. If aluminum oxide, or glass beads are used, subse-
emulsion cleaning. For removing buffing compound, specially quent treatments should include the use of an acid fluoride to
formulated detergent type or modified detergent type buffing ensure that any embedded aluminum oxide or silica is re-
compound removers may also be used. If the deposits of soil moved. However, surfaces of heat-treated alloys that are not
are relatively light and fairly uniformly distributed, a mild machined or buffed should have the heat-treated film removed
etching type cleaner may also be used. A convenient one is a with a deoxidizing etch to obtain uniform electroplating
results.An effective deoxidizing etch is a hot sulfuric-chromic
acid solution (Appendix X1.2). Suitable proprietary deoxidiz-
For details on the proper operation and safety precautions to be followed in
ing etches including some with no chromates are available.
vapor degreasing, see Handbook of Vapor Degreasing, ASTM STP 310, ASTM,
1976. They should be used as recommended by the manufacturer.
B253 − 11 (2022)
5.2.3 For wrought alloys of the UNS A91100 and UNS andadherentlayerofmetalliczinc.Thisprovidesasurfacethat
A93003 types (see Specification B209/B209M) fairly good responds to most of the electroplating procedures for plating
conditioning may be obtained by using the carbonate- other metals on zinc.
phosphate cleaner (Appendix X1.1) followed by a nitric acid 6.3.2 For the immersion step, a highly alkaline solution
dip at room temperature (Appendix X1.6). These alloys do not containing the following components can be used at room
contain interfering constituents and for some applications, this temperature (15 to 27 °C).
method of conditioning may be ample. If a silicate inhibited
Zinc Immersion Solution, Bath I
Sodium hydroxide (commercial) 525 g/L
cleaner is used (see 5.1) the fluoride containing smut remover
Zinc oxide (technical grade) 100 g/L
(Appendix X1.4) is preferred.
6.3.2.1 For best results, the sodium hydroxide must be low
NOTE 4—In accordance with current ASTM practice and for interna-
in sodium carbonate content (preferably under 2 % by weight)
tional usage, the aluminum alloys have been classified in accordance with
and the zinc oxide must be free of contamination.
the Unified Numbering System (UNS) as detailed in Practice E527 and
listed in D556C.
NOTE 5—In the zinc immersion solutions in this standard, the purity of
the ingredients often plays an important role in the successful operation of
5.2.4 Another effective conditioning treatment for removing
theprocess.Thisisparticularlytrueofthezincoxideused.Contamination
the surface oxide film and any undesirable microconstituents
of the zinc oxide with lead or arsenic can be especially troublesome.
comprises the use of a hot sulfuric acid etch (Appendix X1.7).
Proprietary, prepared powdered or liquid zincates are frequently used
The time of the dip depends on the alloy involved. Generally
therefore, since they will have had all raw materials properly checked for
the shorter time is used on castings. This treatment is satisfac-
purity.
tory for all aluminum-magnesium alloys, both wrought and
6.3.2.2 The thickness and quality of the immersion film are
cast. It not only leaves the surface in an excellent condition for
influenced by the conditions of deposition. When deposition is
the deposition of the first metallic layer, but it also eliminates
too rapid, heavy, coarse, crystalline, and porous, non-adherent
the undesirable effects of the magnesium-containing constitu-
deposits are formed. Since the thinner zinc deposits give the
ents in alloys of the UNS A95052, UNS A96061, and UNS
best results, it is recommended that the temperature of the
A96063 types (see Specifications B221 and B221M).
zincate solution be kept below 27 °C and the immersion time
5.3 The following are types of casting alloys containing be from 30 s to 1 min.
high percentages of silicon: UNSA04130, UNSA14130, UNS 6.3.3 A modification of the basic zincate solution in most
applications gives more uniform and satisfactory results. The
A03800, (see Specification B85), UNS A03561, and UNS
A13560, (see Specification B179). A dip at room temperature modified zinc immersion procedure has the following advan-
tages: (1) more uniform coverage by subsequent electroplating
in a mixed acid solution (Appendix X1.8) containing nitric and
hydrofluoricacidsisrecommendedforconditioningthesurface baths, (2) greater operating range for the “double immersion”
version of the treatment (see 6.3.5), and (3) improved resis-
of these alloys. This treatment also removes the heat-treated
film from unpolished, heat-treated castings. tance to corrosion on all electroplated aluminum alloys except
for the UNS A92024 and UNS A97075 alloys. The modified
6. Immersion Deposit/Strike Procedures solution is prepared by dissolving the zinc oxide in a sodium
hydroxide solution and cooling to room temperature. Before
6.1 Followingthecleaningandconditioningtreatments,itis
thebathisdilutedtovolume,awatersolutionofferricchloride
necessary to further treat the surface to obtain adequate
crystals and Rochelle salt (potassium sodium tartrate) is added.
adhesion of an electrodeposited metal on aluminum alloys.
The bath should be stirred while the ferric chloride-Rochelle
This section describes five commercially used procedures:
salt solution is added. The modified zincate solution is made
6.1.1 Zinc immersion with optional copper strike (6.3).
up as follows:
6.1.2 Zinc immersion with neutral nickel strike (6.4).
Zinc Immersion Solution, Bath II
6.1.3 Zincimmersionwithacetatebuffered,nickelglycolate
Sodium hydroxide 525 g/L
strike (6.5).
Zinc oxide 100 g/L
6.1.4 Zinc immersion with an acid or alkaline electroless Ferric chloride hexahydrate 1.0 g/L
Rochelle salt 10 g/L
nickel strike (6.6).
6.3.3.1 This bath should also be operated under 27 °C and
6.1.5 Tin immersion with bronze strike (6.7).
for immersion times of the order of 30 s to 1 min. It is
6.1.6 Electrodeposition of polyamines and polyamides (6.8)
recommended that Bath II be utilized whenever the “double
6.2 The immersion deposit/strike conditions recommended
immersion” treatment is employed. Likewise, it will be found
for each procedure give good results with many alloys of
advantageous on all wrought and cast alloys, except the UNS
aluminum. However, some alloys and tempers may require
A92024 and UNS A97075 types, for corrosion-resistant appli-
slightmodificationoftheprocessingconditionsforbestresults.
cations.
6.3 Zinc Immersion with Optional Copper Strike:
6.3.1 In the zinc immersion step, the oxide film is removed
from the surface to be electroplated and is replaced by a thin 5
Sodium zincate solutions of this general type are now being replaced by newer
modified zincate compositions.
There are proprietary zincate solutions available containing cations other than
iron (also various other additions such as complexing agents or chelating agents or
DS56C Metals and Alloys in the United Numbering System, available from both). A solution containing copper and nickel, as well as zinc, is described by
ASTM Headquarters. Order PCN 05-0564-02. Schaer, G., Plating and Surface Finishing, 68,51 (March 1981).
B253 − 11 (2022)
6.3.3.2 With both of the solutions (Baths I and II), the rinse resulting from attack on the aluminum. It has the disadvantage
immediately after the zinc immersion step is critical. The however in that it increases the load on the waste disposal
activity of the solution increases rapidly with dilution. Because system.
of the high concentrations used, the solution is viscous. If this
6.3.7 The specific gravity of the concentrated solutions
viscous layer is not promptly removed in the rinsing step, the
should be checked occasionally and any loss made up by
diluted film may deposit a loose, spongy zinc film in the rinse,
adding more of the components. Loss of volume by dragout
thereby destroying an otherwise acceptable zinc film.
should be corrected by the addition of more solution of the
Therefore, rinses must be strongly agitated so that this film is
specificcomposition.T
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