1、Designation: B177/B177M 11Endorsed by AmericanElectroplaters SocietyEndorsed by NationalAssociation of Metal FinishersStandard Guide forEngineering Chromium Electroplating1This standard is issued under the fixed designation B177/B177M; the number immediately following the designation indicates the y
2、earof 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 Depart
3、ment of Defense.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 applieddirectly to the basis metal and is usually thicker than decorativedeposits.1.2 The values stated in
4、 either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.3 This gu
5、ide 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 metals. Speci-fied chromium electrodeposits on ferrous surfaces are definedin Specificat
6、ion B650.1.4 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 practices and determine the applica-bility of regulatory limitations prior to use.2. Ref
7、erenced Documents2.1 ASTM Standards:2B183 Practice for Preparation of Low-Carbon Steel forElectroplatingB242 Guide for Preparation of High-Carbon Steel for Elec-troplatingB244 Test Method for Measurement of Thickness ofAnodicCoatings on Aluminum and of Other Nonconductive Coat-ings on Nonmagnetic Ba
8、sis Metals with Eddy-CurrentInstrumentsB253 Guide for Preparation of Aluminum Alloys for Elec-troplatingB254 Practice for Preparation of and Electroplating onStainless SteelB281 Practice for Preparation of Copper and Copper-BaseAlloys for Electroplating and Conversion CoatingsB320 Practice for Prepa
9、ration of Iron Castings for Electro-platingB322 Guide for Cleaning Metals Prior to ElectroplatingB481 Practice for Preparation of Titanium and TitaniumAlloys for ElectroplatingB487 Test Method for Measurement of Metal and OxideCoating Thickness by Microscopical Examination of CrossSectionB499 Test M
10、ethod for Measurement of Coating Thick-nesses by the Magnetic Method: Nonmagnetic Coatings onMagnetic Basis MetalsB504 Test Method for Measurement of Thickness of Me-tallic Coatings by the Coulometric MethodB507 Practice for Design of Articles to Be Electroplated onRacksB558 Practice for Preparation
11、 of Nickel Alloys for Electro-platingB568 Test Method for Measurement of Coating Thicknessby X-Ray SpectrometryB571 Practice for Qualitative Adhesion Testing of MetallicCoatingsB578 Test Method for Microhardness of ElectroplatedCoatingsB602 Test Method for Attribute Sampling of Metallic andInorganic
12、 CoatingsB630 Practice for Preparation of Chromium for Electroplat-ing with ChromiumB650 Specification for Electrodeposited Engineering Chro-mium Coatings on Ferrous SubstratesB697 Guide for Selection of Sampling Plans for Inspectionof Electrodeposited Metallic and Inorganic CoatingsB762 Test Method
13、 of Variables Sampling of Metallic andInorganic CoatingsB849 Specification for Pre-Treatments of Iron or Steel forReducing Risk of Hydrogen EmbrittlementB850 Guide for Post-Coating Treatments of Steel for Re-ducing the Risk of Hydrogen Embrittlement1This guide is under the jurisdiction of ASTM Commi
14、ttee B08 on Metallic andInorganic Coatings and is the direct responsibility of Subcommittee B08.08.01 onEngineering Coatings.Current edition approved June 1, 2011. Published June 2011. Originallyapproved in 1955. Last previous edition approved in 2006 as B177 01(2006)e01.DOI: 10.1520/B0177_B0177M-11
15、.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 website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box
16、 C700, West Conshohocken, PA 19428-2959, United States.B851 Specification for Automated Controlled Shot Peeningof Metallic Articles Prior to Nickel, Autocatalytic Nickel,or Chromium Plating, or as Final FinishF519 Test Method for Mechanical Hydrogen EmbrittlementEvaluation of Plating/Coating Process
17、es and Service Envi-ronments2.2 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 aluminum, nickel alloys, cast iron, steels, copper,copper alloys, and titanium.
18、 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 delamination of the coating.3.2 SmoothnessThe smoothness of the material s
19、urface 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 than that of the substrate.Any mechanical operations that can result in gr
20、inding 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 electrodeposit and thesmoothness required of the electrodeposit, grinding
21、 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 of the electrodeposit can lead to a reduction in thefatigue life of the e
22、lectroplated part. If this is a designconsideration, the use of mechanical methods such as shotpeening (see Specification B851 or MIL-S-13165C, or both) orautofrettage to compressively stress the surface can increasethe fatigue strength. This should be done after any stress-relieving heat treatment.
23、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 operations such as machining, grinding, straightening, orcold-forming, usually will
24、 require one of the stress relief bakesprescribed in Specification B849 prior to electroplating. In allcases, the duration of the bake shall commence from the timeat which the whole of each part attains the specified tempera-ture. This stress relief is essential if hydrogen embrittlementfrom subsequ
25、ent 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 B849 may be baked at a lower temperaturebut not less than 130C for a minimum period of 8 h. Shortertimes at higher temperatures m
26、ay 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 electroplating, par-ticularly with steel substrates. Materials such as aluminum
27、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 taken to meet this importantrequirement, including storage in a noncorrosive en
28、vironment,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 but preferably prior to the final cleaning and etching.Aluminum, titanium, an
29、d 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 chromium electroplating.4.2 See Practice B507 for guidance on rack design, but
30、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 desired areas require rackconstruction designs and methods that are much more exa
31、cting.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 current-carrying capacity ofboth cathode and anode circuits to all parts of the rack.
32、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 requires anodes of specialshapes conforming to the shape of the part or area t
33、o 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 shields, which are parts made ofnonconductive materials and placed to disperse
34、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 the substrate, orstop-offs, which are especially compounded nonconductivetapes,
35、 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 nonconducting) may be used inholes not requiring electroplating to produce a shar
36、p edgewithout grooves around the periphery of the holes.4.2.7 It is very important to remember that improperlyapplied stop-off materials or poorly designed racks can entrap3Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700Robbins Ave., Philadelphia, PA 19111-5094, Attn: NPO
37、DS.B177/B177M 112acids 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 insoluble and noncontaminating to provide the desiredrack life.4.2.9 Components must be pla
38、ced 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 containing 4 to 6 % antimony, 4to 7 % tin, or 1 % silver, or a combination thereof, ar
39、esatisfactory. 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 used for small anodes shouldcontain 0.25 % antimony to obtain the best relationshi
40、p 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 rods or wire may be used forinternal electroplating of small holes, but the latter
41、 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 buildup in the plating solution and poorresults.4.3.1 Some proprietary baths may re
42、quire special anodes,which should be recommended by the supplier.5. Cleaning5.1 Parts to be electroplated may be cleaned in accordancewith Practices B183, B242, B254, B281, B320, B322, B481,B558,orB630, or Guide B253.5.2 Mechanical methods of cleaning steel prior to electro-plating, including abrasi
43、ve 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. Deoxidizing and Etching6.1 Prior to chromium electroplating, most metals needspecial preparation in ord
44、er 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 activate thesubstrate prior to chromium electroplating.6.1.1 AluminumChromium may be electroplated d
45、irectlyonto most cast and wrought aluminum materials used forengineering purposes. Guide B253 offers many useful methodsfor preparing aluminum prior to chromium electroplating. Theremoval of the ever-present, tenacious oxide film on the surfaceof aluminum is what makes electroplating difficult. When
46、 usingtest methods in which a zinc immersion film is applied to thealuminum surface for protection against oxide formation, thearticle to be plated must enter the chromium-plating solutionunder live current.6.1.2 TitaniumLike aluminum, titanium has an ever-present tenacious oxide film that must be r
47、emoved prior toplating. Practice B481 offers many ways to prepare titaniumprior to chromium electroplating.6.1.3 Nickel AlloysSeveral different activation methodsare available in Practice B558 for the preparation of differentnickel alloys. The main difficulty with these materials whenchromium platin
48、g 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 B281 offersmany suitable methods for preparing copper and copper alloysprior to chromium electroplating. In general, only deoxidizingof t
49、he copper or copper alloy surface is necessary for chro-mium electroplating.6.1.5 Stainless SteelPractice B254 offers many suitableactivating procedures for the preparation of stainless steel priorto 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 B320 offers many suitable proce-dures for activating cast iron prior to chromium electroplating.In general, anodic etching in the chromi
