ASTM B253-87(2010)
(Guide)Standard Guide for Preparation of Aluminum Alloys for Electroplating
Standard Guide for Preparation of Aluminum Alloys for Electroplating
SIGNIFICANCE AND USE
Various metals are deposited on aluminum alloys to obtain a decorative or engineering finish. The electroplates applied are usually chromium, nickel, copper, brass, silver, tin, lead, cadmium, zinc, gold, and combinations of these. Silver, tin, or gold is applied to electrical equipment to decrease contact resistance or to improve surface conductivity; brass, copper, nickel, or tin for assembly by soft soldering; chromium to reduce friction and obtain increased resistance to wear; zinc for threaded parts where organic lubricants are not permissible; tin or lead is frequently employed to reduce friction on bearing surfaces. Nickel plus chromium or copper plus nickel plus chromium is used in decorative applications. Nickel plus brass plus lacquer or copper plus nickel plus brass plus lacquer is also used for decorative finishes, sometimes with the brass oxidized and relieved in various ways.
Electroless nickel may be applied as a barrier layer prior to other deposits, or for engineering purposes.
The preparation of aluminum and aluminum alloy mandrels for electroforming is described in Practice .
SCOPE
1.1 This guide covers cleaning and conditioning treatments used before metal deposition (Section 5), and immersion deposit/strike procedures (Section 6) that enhance the adhesion of metals that are subsequently applied to aluminum products by electrodeposition or by autocatalytic chemical reduction.
1.2 The following immersion deposit/strike procedures are covered:
1.2.1 Zinc immersion with optional copper strike (6.3).
1.2.2 Zinc immersion with neutral nickel strike (6.4).
1.2.3 Zinc immersion with acetate-buffered, nickel glycolate strike (6.5).
1.2.4 Zinc immersion with acid or alkaline electroless nickel strike.
1.2.5 Tin immersion with bronze strike (6.6).
1.3 From the processing point of view, these procedures are expected to give deposits on aluminum alloys that are approximately equivalent with respect to adherence. Corrosion performance is affected by many factors, however, including the procedure used to prepare the aluminum alloy for electroplating.
1.4 This guide is intended to aid electroplaters in preparing aluminum and its alloys for electroplating.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
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. For specific precautionary statements see Section 7 and Appendix X1.
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Designation:B253– 87(Reapproved 2010)
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 Department of Defense.
1. Scope 2. Referenced Documents
1.1 This guide covers cleaning and conditioning treatments 2.1 ASTM Standards:
used before metal deposition (Section 5), and immersion B85 Specification for Aluminum-Alloy Die Castings
deposit/strike procedures (Section 6) that enhance the adhesion B179 Specification for Aluminum Alloys in Ingot and
of metals that are subsequently applied to aluminum products Molten Forms for Castings from All Casting Processes
by electrodeposition or by autocatalytic chemical reduction. B209 Specification for Aluminum and Aluminum-Alloy
1.2 The following immersion deposit/strike procedures are Sheet and Plate
covered: B209M Specification for Aluminum and Aluminum-Alloy
1.2.1 Zinc immersion with optional copper strike (6.3). Sheet and Plate (Metric)
1.2.2 Zinc immersion with neutral nickel strike (6.4). B221 Specification for Aluminum and Aluminum-Alloy
1.2.3 Zinc immersion with acetate-buffered, nickel glyco- Extruded Bars, Rods, Wire, Profiles, and Tubes
late strike (6.5). B221M Specification for Aluminum and Aluminum-Alloy
1.2.4 Zinc immersion with acid or alkaline electroless Extruded Bars, Rods, Wire, Profiles, and Tubes (Metric)
nickel strike. B322 Guide for Cleaning Metals Prior to Electroplating
1.2.5 Tin immersion with bronze strike (6.6). B432 Practice for Processing of Mandrels for Electroform-
1.3 From the processing point of view, these procedures are ing
expected to give deposits on aluminum alloys that are approxi- E527 Practice for Numbering Metals and Alloys in the
mately equivalent with respect to adherence. Corrosion perfor- Unified Numbering System (UNS)
mance is affected by many factors, however, including the
3. Significance and Use
procedure used to prepare the aluminum alloy for electroplat-
ing. 3.1 Various metals are deposited on aluminum alloys to
obtain a decorative or engineering finish. The electroplates
1.4 This guide is intended to aid electroplaters in preparing
aluminum and its alloys for electroplating. applied are usually chromium, nickel, copper, brass, silver, tin,
lead, cadmium, zinc, gold, and combinations of these. Silver,
1.5 The values stated in SI units are to be regarded as
standard. No other units of measurement are included in this tin, or gold is applied to electrical equipment to decrease
contact resistance or to improve surface conductivity; brass,
standard.
1.6 This standard does not purport to address all of the copper, nickel, or tin for assembly by soft soldering; chromium
to reduce friction and obtain increased resistance to wear; zinc
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- forthreadedpartswhereorganiclubricantsarenotpermissible;
tin or lead is frequently employed to reduce friction on bearing
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. For specific surfaces. Nickel plus chromium or copper plus nickel plus
chromium is used in decorative applications. Nickel plus brass
precautionary statements see Section 7 and Appendix X1.
plus lacquer or copper plus nickel plus brass plus lacquer is
also used for decorative finishes, sometimes with the brass
oxidized and relieved in various ways.
3.1.1 Electroless nickel may be applied as a barrier layer
prior to other deposits, or for engineering purposes.
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 For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Treatment. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Nov. 1, 2010. Published November 2010. Originally Standards volume information, refer to the standard’s Document Summary page on
´1
approved in 1951. Last previous edition approved in 2005 as B253 – 87 (2005) . the ASTM website.
DOI: 10.1520/B0253-87R10. Withdrawn.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B253– 87 (2010)
3.2 The preparation of aluminum and aluminum alloy man- soak cleaners are used to remove gross soils.Also available are
drels for electroforming is described in Practice B432. a wide range of proprietary cleaners of the “non-etching” type.
Some of these are actually buffered mixtures, similar to the
4. Nature of Aluminum and Its Influence on Preparation
carbonate-phosphate mixture (X1.1) where the so-called non-
etching characteristics are obtained by buffering the solution to
4.1 Microstructure—It is difficult to find a preplating pro-
pH levels where the etching action becomes minimal. Others
cedure that is equally satisfactory for all types and tempers of
aretrulynon-etchingtypeswhereetchingispreventedbyusing
aluminum alloys because the various alloys and products
silicate inhibitors, such as sodium metasilicate (Na SiO ).
behave differently electrochemically due to their different
2 3
These inhibitors always leave a film of aluminum silicate on
compositions and metallurgical structures. When elements are
the surface. When these materials are used, subsequent deoxi-
added for alloying purposes, they may appear in an aluminum
dizing solutions should contain controlled amounts of fluoride
alloy in several different forms: that is, they may be in solid
salts to insure complete removal of the film.
solutioninthealuminumlattice,bepresentasmicroparticlesof
the elements themselves, or be present as particles of interme-
NOTE 1—General information on the cleaning of metals is given in
tallic compounds formed by combination with the aluminum.
Guide B322.
The several solid solution matrices and the 20 or more
5.2 Aftercleaning,aconditioningtreatmentofthesurfaceis
microconstituents that may occur in commercial alloys may
generally required. For this to be effective, it must accomplish
have different chemical reactivities and electropotentials and
two things: (1) remove the original oxide film and (2) remove
their surfaces may not respond uniformly to various chemical
any microconstituents that may interfere with the formation of
and electrochemical treatments. In addition, the response may
a continuous deposited metallic layer or that may react with
be influenced by variations in the microstructure of different
subsequent electroplating solutions.
lots of products of the same alloy. In some cases, these
5.2.1 An effective conditioning treatment is immersion of
variations may be introduced or aggravated by preparation
the work in a warm sodium hydroxide solution (Appendix
processes; for example, the heat generated in buffing. The
X1.3) followed by water rinsing and immersion in a nitric
electroplater needs to know the aluminum alloy that is to be
acid-bifluoride desmutting solution (Appendix X1.4).An alter-
processed in order to select the best electroplating procedure.
native desmutting solution is sulfuric acid-hydrogen peroxide
In the absence of this information, there are so-called universal
(Appendix X1.5).
procedures that may be used. However these will not neces-
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—Inadditiontodifferencesinmicrostructure 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
uniform than the original film. The newly formed oxide film
almost all alloys, and is especially desirable for use with alloys containing
provides a more suitable surface for deposition of the first
magnesium.
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-
5.1 To obtain consistent results for electroplating on alumi-
ments.Normally,heat-treatedfilmsareremovedbymachining,
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 com-
beads may be used. Silicon carbide abrasives should be
pound, 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
hot, aqueous carbonate-phosphate solution (X1.1). Other types
results.An effective deoxidizing etch is a hot sulfuric-chromic
of cleaners are used; for example, mildly alkaline or acidic
acid solution (Appendix X1.2). Suitable proprietary deoxidiz-
ing etches including some with no chromates are available.
They should be used as recommended by the manufacturer.
For details on the proper operation and safety precautions to be followed in
5.2.3 For wrought alloys of the UNS A91100 and UNS
vapor degreasing, see Handbook of Vapor Degreasing, ASTM STP 310, ASTM,
1976. A93003 types (see Specifications B209 and B209M) fairly
B253– 87 (2010)
good conditioning may be obtained by using the carbonate- 6.3.2 For the immersion step, a highly alkaline solution
phosphate cleaner (Appendix X1.1) followed by a nitric acid containing the following components can be used at room
dip at room temperature (Appendix X1.6). These alloys do not temperature (15 to 27°C).
contain interfering constituents and for some applications, this
Zinc Immersion Solution, Bath I
Sodium hydroxide (commercial) 525 g/L
method of conditioning may be ample. If a silicate inhibited
Zinc oxide (technical grade) 100 g/L
cleaner is used (see 5.1) the fluoride containing smut remover
(Appendix X1.4) is preferred. 6.3.2.1 For best results, the sodium hydroxide must be low
in sodium carbonate content (preferably under 2 % by weight)
NOTE 4—In accordance with current ASTM practice and for interna-
and the zinc oxide must be free of contamination.
tional usage, the aluminum alloys have been classified in accordance with
the Unified Numbering System (UNS) as detailed in Practice E527 and
NOTE 5—In the zinc immersion solutions in this standard, the purity of
listed in D556C.
the ingredients often plays an important role in the successful operation of
theprocess.Thisisparticularlytrueofthezincoxideused.Contamination
5.2.4 Another effective conditioning treatment for removing
of the zinc oxide with lead or arsenic can be especially troublesome.
the surface oxide film and any undesirable microconstituents
Proprietary, prepared powdered or liquid zincates are frequently used
comprises the use of a hot sulfuric acid etch (Appendix X1.7).
therefore, since they will have had all raw materials properly checked for
The time of the dip depends on the alloy involved. Generally purity.
the shorter time is used on castings. This treatment is satisfac-
6.3.2.2 The thickness and quality of the immersion film are
tory for all aluminum-magnesium alloys, both wrought and
influenced by the conditions of deposition. When deposition is
cast. It not only leaves the surface in an excellent condition for
too rapid, heavy, coarse, crystalline, and porous, non-adherent
the deposition of the first metallic layer, but it also eliminates
deposits are formed. Since the thinner zinc deposits give the
the undesirable effects of the magnesium-containing constitu-
best results, it is recommended that the temperature of the
ents in alloys of the UNS A95052, UNS A96061, and UNS
zincatesolutionbekeptbelow27°Candtheimmersiontimebe
A96063 types (see Specifications B221 and B221M).
from 30 s to 1 min.
5.3 The following are types of casting alloys containing
6.3.3 A modification of the basic zincate solution in most
high percentages of silicon: UNSA04130, UNSA14130, UNS
applications gives more uniform and satisfactory results. The
A03800, (see Specification B85), UNS A03561, and UNS
modified zinc immersion procedure has the following advan-
A13560, (see Specification B179). A dip at room temperature
tages: (1) more uniform coverage by subsequent electroplating
in a mixed acid solution (Appendix X1.8) containing nitric and
baths, (2) greater operating range for the “double immersion”
hydrofluoricacidsisrecommendedforconditioningthesurface
version of the treatment (see 6.3.5), and (3) improved resis-
of these alloys. This treatment also removes the heat-treated
tance to corrosion on all electroplated aluminum alloys except
film from unpolished, heat-treated castings.
for the UNS A92024 and UNS A97075 alloys. The modified
solution is prepared by dissolving the zinc oxide in a sodium
6. Immersion Depo
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