ASTM B253-11(2017)

Standard Guide for Preparation of Aluminum Alloys for Electroplating

SIGNIFICANCE AND USE
3.1 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.  
3.1.1 Electroless nickel may be applied as a barrier layer prior to other deposits, or for engineering purposes.  
3.2 The preparation of aluminum and aluminum alloy mandrels for electroforming is described in Practice B432.
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.  
1.7 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.

General Information

• Status: Historical
• Publication Date: 30-Apr-2017
• ICS: 25.220.10 - Surface preparation
• Technical Committee: B08 - Metallic and Inorganic Coatings
• Drafting Committee: B08.02 - Pre Treatment

Standards Content (Sample)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: B253 − 11 (Reapproved 2017)
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 Specification for Aluminum and Aluminum-Alloy
1.2.3 Zinc immersion with acetate-buffered, nickel glyco-
Sheet and Plate
late strike (6.5).
B209M Specification for Aluminum and Aluminum-Alloy
1.2.4 Zinc immersion with acid or alkaline electroless
Sheet and Plate (Metric)
nickel strike.
B221 Specification forAluminum andAluminum-Alloy Ex-
1.2.5 Tin immersion with bronze strike (6.6).
truded Bars, Rods, Wire, Profiles, and Tubes
1.3 From the processing point of view, these procedures are
B221M Specification for Aluminum and Aluminum-Alloy
expected to give deposits on aluminum alloys that are approxi- Extruded Bars, Rods, Wire, Profiles, and Tubes (Metric)
mately equivalent with respect to adherence. Corrosion perfor-
B322 Guide for Cleaning Metals Prior to Electroplating
mance is affected by many factors, however, including the B432 Specification for Copper and CopperAlloy Clad Steel
procedure used to prepare the aluminum alloy for electroplat-
Plate
ing.
E527 Practice for Numbering Metals and Alloys in the
Unified Numbering System (UNS)
1.4 This guide is intended to aid electroplaters in preparing
aluminum and its alloys for electroplating.
3. Significance and Use
1.5 The values stated in SI units are to be regarded as
3.1 Various metals are deposited on aluminum alloys to
standard. No other units of measurement are included in this
obtain a decorative or engineering finish. The electroplates
standard.
applied are usually chromium, nickel, copper, brass, silver, tin,
1.6 This standard does not purport to address all of the
lead, cadmium, zinc, gold, and combinations of these. Silver,
safety concerns, if any, associated with its use. It is the
tin, or gold is applied to electrical equipment to decrease
responsibility of the user of this standard to establish appro-
contact resistance or to improve surface conductivity; brass,
priate safety and health practices and determine the applica-
copper, nickel, or tin for assembly by soft soldering; chromium
bility of regulatory limitations prior to use. For specific
to reduce friction and obtain increased resistance to wear; zinc
precautionary statements see Section 7 and Appendix X1.
forthreadedpartswhereorganiclubricantsarenotpermissible;
1.7 This international standard was developed in accor-
tin or lead is frequently employed to reduce friction on bearing
dance with internationally recognized principles on standard-
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
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, 2017. Published May 2017. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1951. Last previous edition approved in 2011 as B253 – 11. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/B0253-11R7. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B253 − 11 (2017)
also used for decorative finishes, sometimes with the brass are relatively light and fairly uniformly distributed, a mild
oxidized and relieved in various ways. etching type cleaner may also be used. A convenient one is a
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
4. Nature of Aluminum and Its Influence on Preparation mixtures, similar to the carbonate-phosphate mixture (Appen-
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
The several solid solution matrices and the 20 or more
Guide B322.
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
alloy.
NOTE 2—When an unmodified sodium hydroxide solution is used,
etchingmaybecomenonuniformandheavyconcrete-likescalesmayform
4.2 OxideFilm—In addition to differences in microstructure
on tank walls and heating surfaces, their development becoming more
that may affect response to preplating treatments, all aluminum
rapid as the concentration of dissolved aluminum increases. The incorpo-
products have an ever-present natural oxide film. This oxide
ration of controlled amounts of deflocculating complexors such as sodium
film can be removed by various acid and alkaline treatments
gluconate, sodium glucoheptonate, certain sugar derivatives, and certain
and even though it reforms immediately on contact with substituted sugar amines will eliminate this problem. Many proprietary
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
5. Cleaning and Conditioning Treatments
important to remove the relatively thick, heat-treated oxide
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
for the deposition of the initial metallic layer. First, the surface 5.2.2.1 In the absence of machining or buffing, controlled
should be free of any oil, grease, buffing compound, or other abrasive blasting may be used to remove this oxide. Fine
foreign material. For removing oil, grease, or buffing abrasives such as aluminum oxide, ceramic beads, or glass
compound, use vapor degreasing, solvent washing, or solvent beads may be used. Silicon carbide abrasives should be
emulsion cleaning. For removing buffing compound, specially avoided. If aluminum oxide, or glass beads are used, subse-
formulated detergent type or modified detergent type buffing quent treatments should include the use of an acid fluoride to
compound removers may also be used. If the deposits of soil ensure that any embedded aluminum oxide or silica is re-
moved. However, surfaces of heat-treated alloys that are not
machined or buffed should have the heat-treated film removed
For details on the proper operation and safety precautions to be followed in
with a deoxidizing etch to obtain uniform electroplating
vapor degreasing, see Handbook of Vapor Degreasing, ASTM STP 310, ASTM,
1976. results.An effective deoxidizing etch is a hot sulfuric-chromic
B253 − 11 (2017)
acid solution (Appendix X1.2). Suitable proprietary deoxidiz- 6.3.1 In the zinc immersion step, the oxide film is removed
ing etches including some with no chromates are available. from the surface to be electroplated and is replaced by a thin
They should be used as recommended by the manufacturer. andadherentlayerofmetalliczinc.Thisprovidesasurfacethat
5.2.3 For wrought alloys of the UNS A91100 and UNS responds to most of the electroplating procedures for plating
A93003 types (see Specifications B209 and B209M) fairly other metals on zinc.
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
method of conditioning may be ample. If a silicate inhibited Sodium hydroxide (commercial) 525 g/L
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
4 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
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.
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
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: B253 − 11 B253 − 11 (Reapproved 2017)
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
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.
1.7 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.
2. Referenced Documents
2.1 ASTM Standards:
B85 Specification for Aluminum-Alloy Die Castings
B179 Specification for Aluminum Alloys in Ingot and Molten Forms for Castings from All Casting Processes
B209 Specification for Aluminum and Aluminum-Alloy Sheet and Plate
B209M Specification for Aluminum and Aluminum-Alloy Sheet and Plate (Metric)
B221 Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes
B221M Specification for Aluminum and Aluminum-Alloy Extruded Bars, Rods, Wire, Profiles, and Tubes (Metric)
B322 Guide for Cleaning Metals Prior to Electroplating
B432 Specification for Copper and Copper Alloy Clad Steel Plate
E527 Practice for Numbering Metals and Alloys in the Unified Numbering System (UNS)
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.
Current edition approved Dec. 15, 2011May 1, 2017. Published December 2011May 2017. Originally approved in 1951. Last previous edition approved in 20102011 as
B253 – 87B253 – 11. (2010). DOI: 10.1520/B0253-11.10.1520/B0253-11R7.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B253 − 11 (2017)
3. Significance and Use
3.1 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.
3.1.1 Electroless nickel may be applied as a barrier layer prior to other deposits, or for engineering purposes.
3.2 The preparation of aluminum and aluminum alloy mandrels for electroforming is described in Practice B432.
4. Nature of Aluminum and Its Influence on Preparation
4.1 Microstructure—It is difficult to find a preplating procedure that is equally satisfactory for all types and tempers of
aluminum alloys because the various alloys and products behave differently electrochemically due to their different compositions
and metallurgical structures. When elements are added for alloying purposes, they may appear in an aluminum alloy in several
different forms: that is, they may be in solid solution in the aluminum lattice, be present as microparticles of the elements
themselves, or be present as particles of intermetallic compounds formed by combination with the aluminum. The several solid
solution matrices and the 20 or more microconstituents that may occur in commercial alloys may have different chemical
reactivities and electropotentials and their surfaces may not respond uniformly to various chemical and electrochemical treatments.
In addition, the response may be influenced by variations in the microstructure of different lots of products of the same alloy. In
some cases, these variations may be introduced or aggravated by preparation processes; for example, the heat generated in buffing.
The electroplater needs to know the aluminum alloy that is to be processed in order to select the best electroplating procedure. In
the absence of this information, there are so-called universal procedures that may be used. However these will not necessarily be
the best or the most economical procedures for the alloy.
4.2 Oxide Film—In addition to differences in microstructure that may affect response to preplating treatments, all aluminum
products have an ever-present natural oxide film. This oxide film can be removed by various acid and alkaline treatments and even
though it reforms immediately on contact with aqueous solutions or air, it then is usually thinner and more uniform than the original
film. The newly formed oxide film provides a more suitable surface for deposition of the first metallic layer.
5. Cleaning and Conditioning Treatments
5.1 To obtain consistent results for electroplating on aluminum alloys, it is essential that the various cleaning and conditioning
treatments provide a surface of uniform activity for the deposition of the initial metallic layer. First, the surface should be free of
any oil, grease, buffing compound, or other foreign material. For removing oil, grease, or buffing compound, use vapor degreasing,
solvent washing, or solvent emulsion cleaning. For removing buffing compound, specially formulated detergent type or modified
detergent type buffing compound removers may also be used. If the deposits of soil are relatively light and fairly uniformly
distributed, a mild etching type cleaner may also be used. A convenient one is a hot, aqueous carbonate-phosphate solution
(Appendix X1.1). Other types of cleaners are used; for example, mildly alkaline or acidic soak cleaners are used to remove gross
soils. Also available are a wide range of proprietary cleaners of the “non-etching” type. Some of these are actually buffered
mixtures, similar to the carbonate-phosphate mixture (Appendix X1.1) where the so-called non-etching characteristics are obtained
by buffering the solution to pH levels where the etching action becomes minimal. Others are truly non-etching types where etching
is prevented by using silicate inhibitors, such as sodium metasilicate (Na SiO ). These inhibitors always leave a film of aluminum
2 3
silicate on the surface. When these materials are used, subsequent deoxidizing solutions should contain controlled amounts of
fluoride salts to insure complete removal of the film.
NOTE 1—General information on the cleaning of metals is given in Guide B322.
5.2 After cleaning, a conditioning treatment of the surface is generally required. For this to be effective, it must accomplish two
things: (1) remove the original oxide film and (2) remove any microconstituents that may interfere with the formation of a
continuous deposited metallic layer or that may react with subsequent electroplating solutions.
5.2.1 An effective conditioning treatment is immersion of the work in a warm sodium hydroxide solution (Appendix X1.3)
followed by water rinsing and immersion in a nitric acid-bifluoride desmutting solution (Appendix X1.4). An alternative
desmutting solution is sulfuric acid-hydrogen peroxide (Appendix X1.5).
NOTE 2—When an unmodified sodium hydroxide solution is used, etching may become nonuniform and heavy concrete-like scales may form on tank
walls and heating surfaces, their development becoming more rapid as the concentration of dissolved aluminum increases. The incorporation of controlled
amounts of deflocculating complexors such as sodium gluconate, sodium glucoheptonate, certain sugar derivatives, and certain substituted sugar amines
will eliminate this problem. Many proprietary etching materials are so modified.
For details on the proper operation and safety precautions to be followed in vapor degreasing, see Handbook of Vapor Degreasing, ASTM STP 310, ASTM, 1976.
B253 − 11 (2017)
NOTE 3—The universal acid mixture (Appendix X1.9) is applicable to almost all alloys, and is especially desirable for use with alloys containing
magnesium.
5.2.2 For heat-treated alloys (alloys in a “T” temper), it is important to remove the relatively thick, heat-treated oxide film before
proceeding with subsequent conditioning treatments. Normally, heat-treated films are removed by machining, or by the polishing
action on metal surfaces that are buffed.
5.2.2.1 In the absence of machining or buffing, controlled abrasive blasting may be used to remove this oxide. Fine abrasives
such as aluminum oxide, ceramic beads, or glass beads may be used. Silicon carbide abrasives should be avoided. If aluminum
oxide, or glass beads are used, subsequent treatments should include the use of an acid fluoride to ensure that any embedded
aluminum oxide or silica is removed. However, surfaces of heat-treated alloys that are not machined or buffed should have the
heat-treated film removed 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 deoxidizing etches including some with no chromates are
available. They should be used as recommended by the manufacturer.
5.2.3 For wrought alloys of the UNS A91100 and UNS A93003 types (see Specifications B209 and B209M) fairly good
conditioning may be obtained by using the carbonate-phosphate cleaner (Appendix X1.1) followed by a nitric acid dip at room
temperature (Appendix X1.6). These alloys do not contain interfering constituents and for some applications, this method of
conditioning may be ample. If a silicate inhibited cleaner is used (see 5.1) the fluoride containing smut remover (Appendix X1.4)
is preferred.
NOTE 4—In accordance with current ASTM practice and for international usage, the aluminum alloys have been classified in accordance with the
Unified Numbering System (UNS) as detailed in Practice E527 and listed in D556C.
5.2.4 Another effective conditioning treatment for removing the surface oxide film and any undesirable microconstituents
comprises the use of a hot sulfuric acid etch (Appendix X1.7). The time of the dip depends on the alloy involved. Generally the
shorter time is used on castings. This treatment is satisfactory for all aluminum-magnesium alloys, both wrought and cast. It not
only leaves the surface in an excellent condition for the deposition of the first metallic layer, but it also eliminates the undesirable
effects of the magnesium-containing constituents in alloys of the UNS A95052, UNS A96061, and UNS A96063 types (see
Specifications B221 and B221M).
5.3 The following are types of casting alloys containing high percentages of silicon: UNS A04130, UNS A14130, UNS A03800,
(see Specification B85), UNS A03561, and UNS A13560, (see Specification B179). A dip at room temperature in a mixed acid
solution (Appendix X1.8) containing nitric and hydrofluoric acids is recommended for conditioning the surface of these alloys.
This treatment also removes the heat-treated film from unpolished, heat-treated castings.
6. Immersion Deposit/Strike Procedures
6.1 Following the cleaning and conditioning treatments, it is necessary to further treat the surface to obtain adequate adhesion
of an electrodeposited metal on aluminum alloys. This section describes five commercially used procedures:
6.1.1 Zinc immersion with optional copper strike (6.3).
6.1.2 Zinc immersion with neutral nickel strike (6.4).
6.1.3 Zinc immersion with acetate buffered, nickel glycolate strike (6.5).
6.1.4 Zinc immersion with an acid or alkaline electroless nickel strike (6.6).
6.1.5 Tin immersion with bronze strike (6.7).
6.1.6 Electrodeposition of polyamines and polyamides (6.8)
6.2 The immersion deposit/strike conditions recommended for each procedure give good results with many alloys of aluminum.
However, some alloys and tempers may require slight modification of the processing conditions for best results.
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 and
adherent layer of metallic zinc. This provides a
...