1、Designation: B253 11Standard 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 revision. A number i
2、n 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 Department of Defense.1. Scope1.1 This guide covers cleaning and conditioning treatmentsused bef
3、ore 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 procedures arecovered:1.2.1
4、 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 bronze strike (6.6).1.3 From
5、 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 for electroplat-ing.1.4
6、 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 thesafety concerns, if
7、 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 X1.2. Referenced Document
8、s2.1 ASTM Standards:2B85 Specification for Aluminum-Alloy Die CastingsB179 Specification for Aluminum Alloys in Ingot andMolten Forms for Castings from All Casting ProcessesB209 Specification for Aluminum and Aluminum-AlloySheet and PlateB209M Specification for Aluminum and Aluminum-AlloySheet and P
9、late (Metric)B221 Specification for Aluminum and Aluminum-AlloyExtruded Bars, Rods, Wire, Profiles, and TubesB221M Specification for Aluminum and Aluminum-AlloyExtruded Bars, Rods, Wire, Profiles, and Tubes (Metric)B322 Guide for Cleaning Metals Prior to ElectroplatingB432 Practice for Processing of
10、 Mandrels for Electroform-ing3E527 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 electroplatesapplied are usually chromium, nickel, copper, brass
11、, 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; chromiumto reduce friction and obtain increased re
12、sistance 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 applications. Nickel plus brassplus lacquer or copper plus nic
13、kel 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 Dec. 15, 2011. Published December 2011. Originallyapproved in 1951. Last previo
14、us edition approved in 2010 as B253 87 (2010).DOI: 10.1520/B0253-11.2For 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 standards Document Summary page onthe ASTM w
15、ebsite.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.also used for decorative finishes, sometimes with the brassoxidized and relieved in various ways.3.1.1 Electroless nickel may be applied as a barrier layerprior to oth
16、er 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 preplating pro-cedure that is equally satisfactory
17、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 aluminumalloy in several different forms: that
18、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 or moremicroconstituents that may occur in c
19、ommercial 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 differentlots of products of the same alloy.
20、 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 procedure.In the absence of this information, there
21、 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, all aluminumproducts have an ever-present n
22、atural 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 oxide filmprovides a more suitable surface for d
23、eposition 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 activityfor the deposition of the initial metallic la
24、yer. First, the surfaceshould be free of any oil, grease, buffing compound, or otherforeign material. For removing oil, grease, or buffing com-pound, use vapor degreasing,4solvent washing, or solventemulsion cleaning. For removing buffing compound, speciallyformulated detergent type or modified dete
25、rgent 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 (X1.1). Other typesof cleaners are used; for example, mildly
26、 alkaline or acidicsoak cleaners are used to remove gross soils.Also available area wide range of proprietary cleaners of the “non-etching” type.Some of these are actually buffered mixtures, similar to thecarbonate-phosphate mixture (X1.1) where the so-called non-etching characteristics are obtained
27、 by buffering the solution topH levels where the etching action becomes minimal. Othersare truly non-etching types where etching is prevented by usingsilicate inhibitors, such as sodium metasilicate (Na2SiO3).These inhibitors always leave a film of aluminum silicate onthe surface. When these materia
28、ls are used, subsequent deoxi-dizing solutions should contain controlled amounts of fluoridesalts to insure complete removal of the film.NOTE 1General information on the cleaning of metals is given inGuide B322.5.2 After cleaning, a conditioning treatment of the surface isgenerally required. For thi
29、s 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 electroplating solutions.5.2.1 An effective conditioning treatment is
30、 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 peroxide(Appendix X1.5).NOTE 2When an unmodified sodium hydro
31、xide 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 controlled amounts of deflocculating complexors such as sodi
32、umgluconate, 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 applicable toalmost all alloys, and is especially desirable for use wi
33、th 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 films are removed by machining,or by the polishing action on
34、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 abrasives should beavoided. If aluminum oxide, or glass beads a
35、re 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-treated film removedwith a deoxidizing etch to obtain uniform elect
36、roplatingresults. An effective deoxidizing etch is a hot sulfuric-chromic4For details on the proper operation and safety precautions to be followed invapor degreasing, see Handbook of Vapor Degreasing, ASTM STP 310, ASTM,1976.B253 112acid solution (Appendix X1.2). Suitable proprietary deoxidiz-ing e
37、tches 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 may be obtained by using the carbonate-phosphate cleaner (Appendix X1
38、.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 (see 5.1) the fluoride containing smut remover(Appendix X1.4) is prefer
39、red.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.55.2.4 Another effective conditioning treatment for removingthe surface oxide
40、 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-tory for all aluminum-magnesium alloys, both wrought andcast. It not o
41、nly 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 UNSA96063 types (see Specifications B221 and B221M).5.3 The following a
42、re 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 (Appendix X1.8) containing nitric andhydrofluoric acids is recommended
43、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 isnecessary to further treat the surface to obtain adequateadhesion of
44、 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 glycolatestrike (6.5).6.1.4 Zinc imme
45、rsion 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 procedure give good results with many alloys ofaluminum. However, some
46、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 electroplated and is replaced by a thinand adherent layer of metallic zinc.
47、 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 solution6containing the following components can be used at roomtemperature (15 to 27C).Zinc Immersion Solution, Bath ISodium hydroxide (comm
48、ercial)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 contamination.NOTE 5In the zinc immersion solutions in this standard, the purity ofthe ingredients
49、 often plays an important role in the successful operation ofthe process. This is particularly true of the zinc oxide used. Contaminationof the zinc oxide with lead or arsenic can be especially troublesome.Proprietary, prepared powdered or liquid zincates are frequently usedtherefore, since they will have had all raw materials properly checked forpurity.6.3.2.2 The thickness and quality of the immersion film areinfluenced by the conditions of deposition. When deposition istoo rapid, heavy, coarse, crystalline, and porous, non-adherentdeposits are formed. Since the thinner zi
