ASTM B177-2001(2006)e1 Standard Guide for Engineering Chromium Electroplating《工程用钢表面镀铬》.pdf

1、Designation: B 177 01 (Reapproved 2006)e1Endorsed by AmericanElectroplaters SocietyEndorsed by NationalAssociation of Metal FinishersStandard Guide forEngineering Chromium Electroplating1This standard is issued under the fixed designation B 177; the number immediately following the designation indic

2、ates the year oforiginal adoption or, in the case of revision, the year of last 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

3、 the Department of Defense.e1NOTEWarning notes in 7.2.1, 7.2.2, and 7.2.3 were editorially updated in April 2006.1. Scope1.1 This guide provides information about the deposition ofchromium on steel for engineering uses. This is sometimescalled “functional” or “hard” chromium and is usually applieddi

4、rectly to the basis metal and is usually thicker than decorativedeposits.1.2 This guide is not intended as a standardized procedure,but as a guide for obtaining smooth, adherent coatings ofchromium of a desired thickness while retaining the requiredphysical and mechanical properties of the base meta

5、ls. Speci-fied chromium electrodeposits on ferrous surfaces are definedin Specification B 650.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health pra

6、ctices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2B 183 Practice for Preparation of Low-Carbon Steel forElectroplatingB 242 Guide for Preparation of High-Carbon Steel forElectroplatingB 244 Test Method for Measurement of Thickne

7、ss of An-odic Coatings on Aluminum and of Other NonconductiveCoatings on Nonmagnetic Basis Metals with Eddy-CurrentInstrumentsB 253 Guide for Preparation of Aluminum Alloys for Elec-troplatingB 254 Practice for Preparation of and Electroplating onStainless SteelB 281 Practice for Preparation of Copp

8、er and Copper-BaseAlloys for Electroplating and Conversion CoatingsB 320 Practice for Preparation of Iron Castings for Electro-platingB 322 Guide for Cleaning Metals Prior to ElectroplatingB 481 Practice for Preparation of Titanium and TitaniumAlloys for ElectroplatingB 487 Test Method for Measureme

9、nt of Metal and OxideCoating Thickness by Microscopical Examination of CrossSectionB 499 Test Method for Measurement of Coating Thick-nesses by the Magnetic Method: Nonmagnetic Coatings onMagnetic Basis MetalsB 504 Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric Met

10、hodB 507 Practice for Design ofArticles to Be Electroplated onRacksB 558 Practice for Preparation of Nickel Alloys for Electro-platingB 568 Test Method for Measurement of Coating Thicknessby X-Ray SpectrometryB 571 Practice for Qualitative Adhesion Testing of MetallicCoatingsB 578 Test Method for Mi

11、crohardness of ElectroplatedCoatingsB 602 Test Method for Attribute Sampling of Metallic andInorganic CoatingsB 630 Practice for Preparation of Chromium for Electro-plating with ChromiumB 650 Specification for Electrodeposited Engineering Chro-mium Coatings on Ferrous SubstratesB 697 Guide for Selec

12、tion of Sampling Plans for Inspectionof Electrodeposited Metallic and Inorganic CoatingsB 762 Test Method of Variables Sampling of Metallic andInorganic CoatingsB 849 Specification for Pre-Treatments of Iron or Steel forReducing Risk of Hydrogen Embrittlement1This guide is under the jurisdiction of

13、ASTM Committee B08 on Metallic andInorganic Coatings and is the direct responsibility of Subcommittee B08.08.01 onEngineering Coatings.Current edition approved April 1, 2006. Published April 2006. Originallyapproved in 1955. Last previous edition approved in 2001 as B 177 01.2For referenced ASTM sta

14、ndards, 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 website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken,

15、 PA 19428-2959, United States.B 850 Guide for Post-Coating Treatments of Steel for Re-ducing the Risk of Hydrogen EmbrittlementB 851 Specification forAutomated Controlled Shot Peeningof Metallic Articles Prior to Nickel, Autocatalytic Nickel,or Chromium Plating, or as Final FinishF 519 Test Method f

16、or Mechanical Hydrogen Embrittle-ment Evaluation of Plating/Coating Processes and ServiceEnvironments2.2 Military Standard:3MIL-S-13165B Shot Peening of Metal Parts3. Substrates3.1 Engineering chromium may be plated directly to thesurface of a number of commonly used engineering metalssuch as alumin

17、um, nickel alloys, cast iron, steels, copper,copper alloys, and titanium. The bond strengths of the chro-mium varies with metallic substrate. Nevertheless, if theprocedures cited in the appropriate references are followed, thebond strength is such that grinding and honing can be con-ducted without d

18、elamination of the coating.3.2 SmoothnessThe smoothness of the material surface tobe electroplated should be adequate to meet the requirementsof the finished product. Chromium electrodeposits do notexhibit leveling, and consequently the surface roughness of theelectrodeposit will always be greater t

19、han that of the substrate.Any mechanical operations that can result in grinding checksor glazing of the metal are detrimental and should be elimi-nated. The required surface smoothness may be obtained bysuitable chemical, mechanical, or electrochemical procedures.Depending upon the thickness of the

20、electrodeposit and thesmoothness required of the electrodeposit, grinding of theelectrodeposit may be required.3.3 Fatigue ConsiderationsCracking that can occur inchromium electrodeposits either as a function of the platingbath chemistry or the plating conditions, or both, or as a resultof grinding

21、of the electrodeposit can lead to a reduction in thefatigue life of the electroplated part. If this is a designconsideration, the use of mechanical methods such as shotpeening (see Specification B 851 or MIL-S-13165C, or both)or autofrettage to compressively stress the surface can increasethe fatigu

22、e strength. This should be done after any stress-relieving heat treatment.3.4 High-Strength Steel Stress Relief:3.4.1 All steel parts having an ultimate tensile strength of1000 MPa (150 000 psi, approximately 32 HRC) or greater,which may contain residual stress caused by various fabrica-tion operati

23、ons such as machining, grinding, straightening, orcold-forming, usually will require one of the stress relief bakesprescribed in Specification B 849 prior to electroplating. In allcases, the duration of the bake shall commence from the timeat which the whole of each part attains the specified temper

24、a-ture. This stress relief is essential if hydrogen embrittlementfrom subsequent operations is to be avoided.3.4.2 Parts having surface-hardened areas that would sufferan unacceptable reduction in hardness by baking in accordancewith Specification B 849 may be baked at a lower temperaturebut not les

25、s than 130C for a minimum period of 8 h. Shortertimes at higher temperatures may be used, if the resulting lossin surface hardness is acceptable.3.5 OxidationAll possible precautions should be taken toprevent oxidation of the metal surface between the finaloperations of mechanical preparation and el

26、ectroplating, par-ticularly with steel substrates. Materials such as aluminum andtitanium have an inherent oxide film on the surface that canonly be removed or minimized just prior to the electroplatingprocess (see 6.1.1 and 6.1.2). When conditions are especiallyunfavorable, definite steps must be t

27、aken to meet this importantrequirement, including storage in a noncorrosive environment,or the use of a suitable coating to exclude air and moisture.4. Racks and Anodes4.1 Steel, cast iron, and stainless steel parts to be electro-plated may be racked at any convenient stage in the preparatoryprocess

28、 but preferably prior to the final cleaning and etching.Aluminum, titanium, and certain nickel alloys may need tohave cleaning and etching operations done before racking dueto entrapment of cleaning and etching solutions in the platingrack which can result in adhesion failures due to seepageduring c

29、hromium electroplating.4.2 See Practice B 507 for guidance on rack design, but notethat while the general principles of good racking as used inother electroplating processes apply, the use of much highercurrent densities and the desirability of securing coatings ofuniform thickness and quality on de

30、sired areas require rackconstruction designs and methods that are much more exacting.The design of racks for chromium electroplating on the variousbase metals previously mentioned for functional use shouldprovide for the following to the greatest possible extent.4.2.1 There must be sufficient curren

31、t-carrying capacity ofboth cathode and anode circuits to all parts of the rack.4.2.2 There must be positive electrical contact to the parts tobe electroplated, to the anodes, and to the tank contact bus bars.4.2.3 There must be uniform current distribution on theparts to be electroplated. This often

32、 requires anodes of specialshapes conforming to the shape of the part or area to beelectroplated.4.2.4 It may be necessary to use thieves, robbers, or guards,which are auxiliary metallic conductors placed near points ofabnormally high current density to attract the current awayfrom such points; and

33、shields, which are parts made ofnonconductive materials and placed to disperse the current inareas where it tends to concentrate unduly.4.2.5 It is important to protect areas that are to remain freeof any chromium electroplate by the use of masks made ofrigid, nonconductive materials placed against

34、the substrate, orstop-offs, which are especially compounded nonconductivetapes, waxes, lacquers, or plastics for the protection of suchsubstrates. Lead and aluminum tapes will provide a sharp lineof demarcation between coated and uncoated areas with aminimum of buildup.4.2.6 Plugs (conducting and no

35、nconducting) may be used inholes not requiring electroplating to produce a sharp edgewithout grooves around the periphery of the holes.3Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPODS.B 177 01 (2006)e124.2.7 It is very

36、 important to remember that improperlyapplied stop-off materials or poorly designed racks can entrapacids that can cause corrosion of the basis material or contami-nation of the solutions used in subsequent operations, or both.4.2.8 Construction materials must be used that are suffi-ciently insolubl

37、e and noncontaminating to provide the desiredrack life.4.2.9 Components must be placed in such positions that gasfrom the parts, rack, thieves, masks, and anodes escapes freelyand does not become entrapped so as to prevent electroplatingon areas that should be electroplated.4.3 AnodesLead anodes con

38、taining 4 to 6 % antimony, 4to 7 % tin, or 1 % silver, or a combination thereof, aresatisfactory. Chemical lead is also satisfactory where hardnessand rigidity are not important. However, it tends to form greatquantities of scale that may fall off on the work and causepitting or roughness. Lead wire

39、 used for small anodes shouldcontain 0.25 % antimony to obtain the best relationship be-tween rigidity and ductility in close tolerance areas. Lead-sheathed steel, copper, or silver may be used when indicated byrequirements for strength or conductivity. Platinum, platinum-clad niobium, or even steel

40、 rods or wire may be used forinternal electroplating of small holes, but the latter willcontaminate the bath with iron. If the anode contains little or nolead, the reoxidation of trivalent chromium to the hexavalentstate will not take place or will be seriously impaired, whichwill lead to trivalent

41、buildup in the plating solution and poorresults.4.3.1 Some proprietary baths may require special anodes,which should be recommended by the supplier.5. Cleaning5.1 Parts to be electroplated may be cleaned in accordancewith Practices B 183, B 242, B 254, B 281, B 320, B 322,B 481, B 558,orB 630, or Gu

42、ide B 253.5.2 Mechanical methods of cleaning steel prior to electro-plating, including abrasive blasting or light grinding, are alsosuitable. If parts have been shot-peened to develop a compres-sively stressed surface, it is important to avoid removing thatsurface by excessive grinding.6. Deoxidizin

43、g and Etching6.1 Prior to chromium electroplating, most metals needspecial preparation in order to achieve maximum adhesion ofthe chromium to the substrate. Depending on the type andnature of the metal and prior surface preparation steps, variousdeoxidation and etching methods may be used to activat

44、e thesubstrate prior to chromium electroplating.6.1.1 AluminumChromium may be electroplated directlyonto most cast and wrought aluminum materials used forengineering purposes. Guide B 253 offers many useful meth-ods for preparing aluminum prior to chromium electroplating.The removal of the ever-pres

45、ent, tenacious oxide film on thesurface of aluminum is what makes electroplating difficult.When using test methods in which a zinc immersion film isapplied to the aluminum surface for protection against oxideformation, the article to be plated must enter the chromium-plating solution under live curr

46、ent.6.1.2 TitaniumLike aluminum, titanium has an ever-present tenacious oxide film that must be removed prior toplating. Practice B 481 offers many ways to prepare titaniumprior to chromium electroplating.6.1.3 Nickel AlloysSeveral different activation methodsare available in Practice B 558 for the

47、preparation of differentnickel alloys. The main difficulty with these materials whenchromium plating is polarization of the nickel alloy surfaceprior to plating which results in deactivation of the material andskip plating.6.1.4 Copper and Copper AlloysPractice B 281 offersmany suitable methods for

48、preparing copper and copper alloysprior to chromium electroplating. In general, only deoxidizingof the copper or copper alloy surface is necessary for chro-mium electroplating.6.1.5 Stainless SteelPractice B 254 offers many suitableactivating procedures for the preparation of stainless steel priorto

49、 chromium electroplating. Some stainless steels benefit froma Woods nickel strike prior to chromium electroplating. Polar-ized surfaces in high-nickel stainless steels can cause skipplating if not properly activated.6.1.6 Cast IronPractice B 320 offers many suitable pro-cedures for activating cast iron prior to chromium electroplat-ing. In general, anodic etching in the chromium platingsolution is not recommended. Due to the high carbon content iniron castings, anodic etching leaves a carbon smut on thesurface of the metal which results in poor adhesion of thechromium.6.