1、Designation: B253 11 (Reapproved 2017)Standard Guide forPreparation of Aluminum Alloys for Electroplating1This standard is issued under the fixed designation B253; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last re
2、vision. A number in parentheses indicates the year of last reapproval. Asuperscript 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. Scope1.1 This guide covers cleaning and conditio
3、ning treatmentsused before metal deposition (Section 5), and immersiondeposit/strike procedures (Section 6) that enhance the adhesionof metals that are subsequently applied to aluminum productsby electrodeposition or by autocatalytic chemical reduction.1.2 The following immersion deposit/strike proc
4、edures arecovered: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 glyco-late strike (6.5).1.2.4 Zinc immersion with acid or alkaline electrolessnickel strike.1.2.5 Tin immersion with bronz
5、e strike (6.6).1.3 From the processing point of view, these procedures areexpected to give deposits on aluminum alloys that are approxi-mately equivalent with respect to adherence. Corrosion perfor-mance is affected by many factors, however, including theprocedure used to prepare the aluminum alloy
6、for electroplat-ing.1.4 This guide is intended to aid electroplaters in preparingaluminum and its alloys for electroplating.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard does not purport to address all of
7、 thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use. For specificprecautionary statements see Section 7 and Appendix X1
8、.1.7 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers t
9、o Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2B85 Specification for Aluminum-Alloy Die CastingsB179 Specification for Aluminum Alloys in Ingot and Mol-ten Forms for Castings from All Casting ProcessesB209 Specification for Aluminum and Aluminum-AlloySheet and PlateB209M Specific
10、ation for Aluminum and Aluminum-AlloySheet and Plate (Metric)B221 Specification for Aluminum and Aluminum-Alloy Ex-truded Bars, Rods, Wire, Profiles, and TubesB221M Specification for Aluminum and Aluminum-AlloyExtruded Bars, Rods, Wire, Profiles, and Tubes (Metric)B322 Guide for Cleaning Metals Prio
11、r to ElectroplatingB432 Specification for Copper and Copper Alloy Clad SteelPlateE527 Practice for Numbering Metals and Alloys in theUnified Numbering System (UNS)3. Significance and Use3.1 Various metals are deposited on aluminum alloys toobtain a decorative or engineering finish. The electroplates
12、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 decreasecontact resistance or to improve surface conductivity; brass,copper, nickel, or tin for assembly by soft soldering;
13、 chromiumto reduce friction and obtain increased resistance to wear; zincfor threaded parts where organic lubricants are not permissible;tin or lead is frequently employed to reduce friction on bearingsurfaces. Nickel plus chromium or copper plus nickel pluschromium is used in decorative application
14、s. Nickel plus brassplus lacquer or copper plus nickel plus brass plus lacquer is1This guide is under the jurisdiction of ASTM Committee B08 on Metallic andInorganic Coatings and is the direct responsibility of Subcommittee B08.02 on PreTreatment.Current edition approved May 1, 2017. Published May 2
15、017. Originallyapproved in 1951. Last previous edition approved in 2011 as B253 11. DOI:10.1520/B0253-11R7.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the stand
16、ards Document Summary page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Deci
17、sion on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1also used for decorative finishes, sometimes with the brassoxidized and relieved in various ways.3.1.1 Electroless nickel m
18、ay be applied as a barrier layerprior to other deposits, or for engineering purposes.3.2 The preparation of aluminum and aluminum alloy man-drels for electroforming is described in Practice B432.4. Nature of Aluminum and Its Influence on Preparation4.1 MicrostructureIt is difficult to find a preplat
19、ing pro-cedure that is equally satisfactory for all types and tempers ofaluminum alloys because the various alloys and productsbehave differently electrochemically due to their differentcompositions and metallurgical structures. When elements areadded for alloying purposes, they may appear in an alu
20、minumalloy in several different forms: that is, they may be in solidsolution in the aluminum lattice, be present as microparticles ofthe elements themselves, or be present as particles of interme-tallic compounds formed by combination with the aluminum.The several solid solution matrices and the 20
21、or moremicroconstituents that may occur in commercial alloys mayhave different chemical reactivities and electropotentials andtheir surfaces may not respond uniformly to various chemicaland electrochemical treatments. In addition, the response maybe influenced by variations in the microstructure of
22、differentlots of products of the same alloy. In some cases, thesevariations may be introduced or aggravated by preparationprocesses; for example, the heat generated in buffing. Theelectroplater needs to know the aluminum alloy that is to beprocessed in order to select the best electroplating procedu
23、re.In the absence of this information, there are so-called universalprocedures that may be used. However these will not neces-sarily be the best or the most economical procedures for thealloy.4.2 Oxide FilmIn addition to differences in microstructurethat may affect response to preplating treatments,
24、 all aluminumproducts have an ever-present natural oxide film. This oxidefilm can be removed by various acid and alkaline treatmentsand even though it reforms immediately on contact withaqueous solutions or air, it then is usually thinner and moreuniform than the original film. The newly formed oxid
25、e filmprovides a more suitable surface for deposition of the firstmetallic layer.5. Cleaning and Conditioning Treatments5.1 To obtain consistent results for electroplating on alumi-num alloys, it is essential that the various cleaning andconditioning treatments provide a surface of uniform activityf
26、or the deposition of the initial metallic layer. First, the surfaceshould be free of any oil, grease, buffing compound, or otherforeign material. For removing oil, grease, or buffingcompound, use vapor degreasing,3solvent washing, or solventemulsion cleaning. For removing buffing compound, specially
27、formulated detergent type or modified detergent type buffingcompound removers may also be used. If the deposits of soilare relatively light and fairly uniformly distributed, a mildetching type cleaner may also be used. A convenient one is ahot, aqueous carbonate-phosphate solution (Appendix X1.1).Ot
28、her types of cleaners are used; for example, mildly alkalineor acidic soak cleaners are used to remove gross soils. Alsoavailable are a wide range of proprietary cleaners of the“non-etching” type. Some of these are actually bufferedmixtures, similar to the carbonate-phosphate mixture (Appen-dix X1.1
29、) where the so-called non-etching characteristics areobtained by buffering the solution to pH levels where theetching action becomes minimal. Others are truly non-etchingtypes where etching is prevented by using silicate inhibitors,such as sodium metasilicate (Na2SiO3). These inhibitors al-ways leav
30、e a film of aluminum silicate on the surface. Whenthese materials are used, subsequent deoxidizing solutionsshould contain controlled amounts of fluoride salts to insurecomplete removal of the film.NOTE 1General information on the cleaning of metals is given inGuide B322.5.2 After cleaning, a condit
31、ioning treatment of the surface isgenerally required. For this to be effective, it must accomplishtwo things: (1) remove the original oxide film and (2) removeany microconstituents that may interfere with the formation ofa continuous deposited metallic layer or that may react withsubsequent electrop
32、lating solutions.5.2.1 An effective conditioning treatment is immersion ofthe work in a warm sodium hydroxide solution (AppendixX1.3) followed by water rinsing and immersion in a nitricacid-bifluoride desmutting solution (Appendix X1.4). An alter-native desmutting solution is sulfuric acid-hydrogen
33、peroxide(Appendix X1.5).NOTE 2When an unmodified sodium hydroxide solution is used,etching may become nonuniform and heavy concrete-like scales may formon tank walls and heating surfaces, their development becoming morerapid as the concentration of dissolved aluminum increases. The incorpo-ration of
34、 controlled amounts of deflocculating complexors such as sodiumgluconate, sodium glucoheptonate, certain sugar derivatives, and certainsubstituted sugar amines will eliminate this problem. Many proprietaryetching materials are so modified.NOTE 3The universal acid mixture (Appendix X1.9) is applicabl
35、e toalmost all alloys, and is especially desirable for use with alloys containingmagnesium.5.2.2 For heat-treated alloys (alloys in a “T” temper), it isimportant to remove the relatively thick, heat-treated oxidefilm before proceeding with subsequent conditioning treat-ments. Normally, heat-treated
36、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, controlledabrasive blasting may be used to remove this oxide. Fineabrasives such as aluminum oxide, ceramic beads, or glassbeads may be used. Silicon carbide ab
37、rasives should beavoided. If aluminum oxide, or glass beads are used, subse-quent treatments should include the use of an acid fluoride toensure that any embedded aluminum oxide or silica is re-moved. However, surfaces of heat-treated alloys that are notmachined or buffed should have the heat-treate
38、d film removedwith a deoxidizing etch to obtain uniform electroplatingresults. An effective deoxidizing etch is a hot sulfuric-chromic3For details on the proper operation and safety precautions to be followed invapor degreasing, see Handbook of Vapor Degreasing, ASTM STP 310, ASTM,1976.B253 11 (2017
39、)2acid 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.5.2.3 For wrought alloys of the UNS A91100 and UNSA93003 types (see Specifications B209 and B209M) fairlygood conditioning m
40、ay be obtained by using the carbonate-phosphate cleaner (Appendix X1.1) followed by a nitric aciddip at room temperature (Appendix X1.6). These alloys do notcontain interfering constituents and for some applications, thismethod of conditioning may be ample. If a silicate inhibitedcleaner is used (se
41、e 5.1) the fluoride containing smut remover(Appendix X1.4) is preferred.NOTE 4In accordance with current ASTM practice and for interna-tional usage, the aluminum alloys have been classified in accordance withthe Unified Numbering System (UNS) as detailed in Practice E527 andlisted in D556C.45.2.4 An
42、other effective conditioning treatment for removingthe surface oxide film and any undesirable microconstituentscomprises the use of a hot sulfuric acid etch (Appendix X1.7).The time of the dip depends on the alloy involved. Generallythe shorter time is used on castings. This treatment is satisfac-to
43、ry for all aluminum-magnesium alloys, both wrought andcast. It not only leaves the surface in an excellent condition forthe deposition of the first metallic layer, but it also eliminatesthe undesirable effects of the magnesium-containing constitu-ents in alloys of the UNS A95052, UNS A96061, and UNS
44、A96063 types (see Specifications B221 and B221M).5.3 The following are types of casting alloys containinghigh percentages of silicon: UNS A04130, UNS A14130, UNSA03800, (see Specification B85), UNS A03561, and UNSA13560, (see Specification B179). A dip at room temperaturein a mixed acid solution (Ap
45、pendix X1.8) containing nitric andhydrofluoric acids is recommended for conditioning the surfaceof these alloys. This treatment also removes the heat-treatedfilm from unpolished, heat-treated castings.6. Immersion Deposit/Strike Procedures6.1 Following the cleaning and conditioning treatments, it is
46、necessary to further treat the surface to obtain adequateadhesion 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
47、 with acetate buffered, nickel glycolatestrike (6.5).6.1.4 Zinc immersion with an acid or alkaline electrolessnickel 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 recommendedfor each pro
48、cedure give good results with many alloys ofaluminum. However, some alloys and tempers may requireslight 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 removedfrom the surface to be electro
49、plated and is replaced by a thinand adherent layer of metallic zinc. This provides a surface thatresponds to most of the electroplating procedures for platingother metals on zinc.6.3.2 For the immersion step, a highly alkaline solution5containing the following components can be used at roomtemperature (15 to 27C).Zinc Immersion Solution, Bath ISodium hydroxide (commercial)Zinc oxide (technical grade)525 g/L100 g/L6.3.2.1 For best results, the sodium hydroxide must be lowin sodium carbonate content (preferably under 2 % by weight)and the zinc oxide must be free of contaminatio
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