ASTM B253-1987(2005)e1 Standard Guide for Preparation of Aluminum Alloys for Electroplating《电镀用铝合金的制备标准指南》.pdf

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1、Designation: B 253 87 (Reapproved 2005)e1Standard Guide forPreparation of Aluminum Alloys for Electroplating1This standard is issued under the fixed designation B 253; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of las

2、t revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.e1NOTEThe Warning notes in 7.1 and X1.8 were update

3、d in October 2005.1. Scope1.1 This guide covers cleaning and conditioning 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 autocatalyt

4、ic chemical reduction.1.2 The following immersion deposit/strike procedures 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 aci

5、d or alkaline electrolessnickel strike.1.2.5 Tin immersion with bronze 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

6、, however, including theprocedure used to prepare the aluminum alloy for electroplat-ing.1.4 This guide is intended to aid electroplaters in preparingaluminum and its alloys for electroplating.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. I

7、t 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.2. Referenced Documents2.1 ASTM Standards:2B85 Specificat

8、ion for Aluminum-Alloy Die CastingsB 179 Specification for Aluminum Alloys in Ingot andMolten Forms for Castings from All Casting ProcessesB 209 Specification for Aluminum and Aluminum-AlloySheet and PlateB 209M Specification for Aluminum and Aluminum-AlloySheet and Plate MetricB 221 Specification f

9、or Aluminum and Aluminum-AlloyExtruded Bars, Rods, Wire, Profiles, and TubesB 221M Specification for Aluminum and Aluminum-AlloyExtruded Bars, Rods, Wire, Profiles, and Tubes MetricB 322 Guide for Cleaning Metals Prior to ElectroplatingB 431 Practice for Processing of Mandrels for Electroform-ing3E

10、527 Practice for Numbering Metals and Alloys (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, silver, tin,lead, cadmium, zinc, gold, and combinations of t

11、hese. 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 resistance to wear; zincfor threaded parts where organic lubrica

12、nts are not permissible;tin or lead is frequently employed to reduce friction on bearing1This 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 Sept. 15, 2005. Publi

13、shed October 2005. Originallyapproved in 1951. Last previous edition approved in 1999 as B 253 87 (1999)e1.2For 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

14、ards Document Summary page onthe ASTM website.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.surfaces. Nickel plus chromium or copper plus nickel pluschromium is used in decorative applications. Nickel plus brassplus lacq

15、uer or copper plus nickel plus brass plus lacquer isalso 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 other deposits, or for engineering purposes.3.2 The preparation of aluminum and alum

16、inum alloy man-drels for electroforming is described in Practice B 431.4. Nature of Aluminum and Its Influence on Preparation4.1 MicrostructureIt is difficult to find a preplating pro-cedure that is equally satisfactory for all types and tempers ofaluminum alloys because the various alloys and produ

17、ctsbehave 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 is, they may be in solidsolution in the aluminum lattice, be present as micropar

18、ticles 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 commercial alloys mayhave different chemical reactivities and electropotentials a

19、ndtheir 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. In some cases, thesevariations may be introduced or aggravated by preparationpr

20、ocesses; 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 are so-called universalprocedures that may be used. However these will not nece

21、s-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 natural oxide film. This oxidefilm can be removed by various acid and alkaline tr

22、eatmentsand 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 deposition of the firstmetallic layer.5. Cleaning and Conditioning Treatments5.1

23、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 layer. First, the surfaceshould be free of any oil, grease, buffing compound, or o

24、therforeign 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 detergent type buffingcompound removers may also be used. If the deposits of soilare

25、 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 alkaline or acidicsoak cleaners are used to remove gross soils.Also available a

26、rea 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 by buffering the solution topH levels where the etching action becomes minimal.

27、 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 materials are used, subsequent deoxi-dizing solutions should contain controlled amounts

28、 of fluoridesalts to insure complete removal of the film.NOTE 1General information on the cleaning of metals is given inGuide B 322.5.2 After cleaning, a conditioning treatment of the surface isgenerally required. For this to be effective, it must accomplishtwo things: (1) remove the original oxide

29、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 immersion ofthe work in a warm sodium hydroxide solution (AppendixX1.3) follow

30、ed 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 hydroxide solution is used,etching may become nonuniform and heavy concrete-like sca

31、les 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 sodiumgluconate, sodium glucoheptonate, certain sugar derivatives, and certainsubst

32、ituted 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 with alloys containingmagnesium.5.2.2 For heat-treated alloys (alloys in a “T” te

33、mper), 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 metal surfaces that are buffed.5.2.2.1 In the absence of machining or buffing,

34、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 are used, subse-quent treatments should include the use of an acid fluoride toen

35、sure 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 removed4For details on the proper operation and safety precautions to be followed invapor degreasing, see Handbook of Vapor Degreasin

36、g, ASTM STP 310, ASTM,1976.B 253 87 (2005)e12with a deoxidizing etch to obtain uniform electroplatingresults. An effective deoxidizing etch is a hot sulfuric-chromicacid solution (Appendix X1.2). Suitable proprietary deoxidiz-ing etches including some with no chromates are available.They should be u

37、sed as recommended by the manufacturer.5.2.3 For wrought alloys of the UNS A91100 and UNSA93003 types (see Specifications B 209 and B 209M) fairlygood conditioning may be obtained by using the carbonate-phosphate cleaner (Appendix X1.1) followed by a nitric aciddip at room temperature (Appendix X1.6

38、). 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 preferred.NOTE 4In accordance with current ASTM practice and for interna-

39、tional usage, the aluminum alloys have been classified in accordance withthe Unified Numbering System (UNS) as detailed in Practice E 527 andlisted in D556C.55.2.4 Another effective conditioning treatment for removingthe surface oxide film and any undesirable microconstituentscomprises the use of a

40、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 only leaves the surface in an excellent condition forthe deposition

41、 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 B 221 and B 221M).5.3 The following are types of casting alloys containinghigh percentages of silicon

42、: UNS A04130, UNS A14130, UNSA03800, (see Specification B85), UNS A03561, and UNSA13560, (see Specification B 179). A dip at room temperaturein a mixed acid solution (Appendix X1.8) containing nitric andhydrofluoric acids is recommended for conditioning the surfaceof these alloys. This treatment als

43、o 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 an electrodeposited metal on aluminum alloys.This section desc

44、ribes 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 immersion with an acid or alkaline electrolessnickel strike (6.6).6

45、.1.5 Tin immersion with bronze strike (6.7).6.2 The immersion deposit/strike conditions recommendedfor each procedure 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 O

46、ptional 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. This provides a surface thatresponds to most of the electroplating procedures for platingother metals on zinc.6.3.2 For

47、the immersion step, a highly alkaline solution6containing 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 carb

48、onate 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 often plays an important role in the successful operation ofthe process. This is particularly true of the zinc oxide use

49、d. 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 zinc deposits give thebest results, it is recommended that the temperature of thezincate solution be kept below 27C an