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1、SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefr
2、om, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. QUESTIONS REGARDING THIS DOCUMENT: (724) 772-8512 FAX: (724) 776-0243 TO PLACE A DOCU
3、MENT ORDER; (724) 776-4970 FAX: (724) 776-0790 SAE WEB ADDRESS http:/www.sae.org Copyright 1991 Society of Automotive Engineers, Inc. All rights reserved.Printed in U.S.A. SURFACE VEHICLE 400 Commonwealth Drive, Warrendale, PA 15096-0001 STANDARD An American National Standard J1837 ISSUED JUN91 Issu
4、ed1991-06-14 ELECTROPLATE REQUIREMENTS FOR DECORATIVE CHROMIUM DEPOSITS ON ZINC BASE MATERIALS USED FOR EXTERIOR ORNAMENTATION ForewordThis Document has not changed other than to put it into the new SAE Technical standards board Format. 1.ScopeThis SAE Standard covers the physical and performance re
5、quirements for electrodeposited copper, nickel, and chromium deposits on exterior ornamentation fabricated from die cast zinc alloys (SAE J468 alloys 903 and 925), and wrought zinc strip (ASTM B 69). This type of coating is designed to provide a high degree of corrosion resistance for automotive, tr
6、uck, marine, and farm usage where a bright, decorative finish is desired. 1.1PurposeThis document details the physical and chemical properties that are necessary to optimize coating appearance and durability of decoratively plated parts. When properly applied, the electroplate described in this docu
7、ment has a bright, highly reflective, and specular finish with an inherently high degree of corrosion resistance. The coatings resistance to a corrosive environment is highly dependent on the proper maintenance of the processes used to produce the coating. Since the treatment of processing variables
8、 is outside the scope of this document, it is important for applicators of this coating to develop an intimate knowledge of their process, and control all parameters that affect the quality of the end product. The use of techniques such as statistical process control (SPC), capability studies, desig
9、n of experiments, process optimization, etc., are critical to produce a material of consistently high quality. The subjects included in this document are: substrate preparation, metal finishing, plate thickness, electrochemical potential difference, ductility, chromium microdiscontinuity, accelerate
10、d corrosion, adhesion, bend testing, and sampling. The appropriate specification limits and test methods are described in each section. Where possible, the test methods specified are well established and accepted within the plating industry. In a few instances, several test methods are specified. In
11、 these cases, it is up to the purchaser and supplier to agree on the test method to be used. 2.References 2.1Applicable PublicationsThe following publications form a part of this specification to the extent specified herein. The latest issue of SAE publications shall apply. 2.1.1SAE PUBLICATIONAvail
12、able from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001. SAE J468Zinc Alloy Ingot and Die Casting Compositions SAE J1837 Issued JUN91 -2- 2.1.2ASTM PUBLICATIONSAvailable from ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959. ASTM B 69Specification for Rolled Zinc ASTM B 252Prep
13、aration of Zinc Alloy Die Castings for Electroplating and Conversion Coatings ASTM B 368Copper-Accelerated Acetic Acid-Salt Spray (Fog) Testing (CASS Test) ASTM B 374Standard Definitions of Terms Relating to Electroplating ASTM B 456Electrodeposited Coatings of Copper Plus Nickel Plus Chromium and N
14、ickel Plus Chromium ASTM B 487Measurement of Metal and Oxide Coating Thickness by Microscopical Examination of a Cross Section ASTM B 490Micrometer Bend Test for Ductility of Electrodeposits ASTM B 504Measurement of Thickness of Metallic Coatings by the Coulometric Method ASTM B 507Design of Article
15、s to be Electroplated on Racks ASTM B 537Rating of Electroplated Panels Subjected to Atmospheric Exposure ASTM B 556Measurement of Thin Chromium Coatings by the Spot Test ASTM B 571Adhesion of Metallic Coatings ASTM B 602Attribute Sampling of Electrodeposited Metallic Coatings and Related Finishes A
16、STM B 697Selection of Sampling Plans for Inspection of Electrodeposited Metallic Coatings and Related Finishes on Products ASTM B 762Variables Sampling of Metallic and Inorganic Coatings ASTM B 764Simultaneous Thickness and Electrochemical Potential Determination of Individual Layers in Multilayer N
17、ickel Deposit (STEP Test) 3.Definitions 3.1Significant SurfacesThese are defined as surfaces that are visible when the finished component is assembled onto the vehicle and is observed in normal viewing position. Nonsignificant surfaces that may cause corrosion products to run onto significant surfac
18、es are significant. Also, nonvisible surfaces, when designated by the customer, are significant. 3.2MicrodiscontinuousA chromium deposit in which microscopic voids exist in the chromium, exposing the underlying nickel layer. The production of suitable microscopic voids or sites in the chromium layer
19、 causes a dispersion of the corrosion potential over a relatively large surface area. The resulting corrosion potential dispersion reduces the effects of localized high corrosion potentials and the associated large corrosion pits. 3.2.1ASTM B 374 provides definitions of the more common terms related
20、 to plating. 4.AppearanceAll parts manufactured to this document shall meet the visual requirements for color, luster, and other specific finish standards agreed on between the customer and supplier, on all significant surfaces. Standard panels or typical production parts should be used to define th
21、e various appearance levels for major surfaces and parting line finishes. Various classes or types of finish may be specified by the purchaser. The production drawing should indicate, via symbols or notes, the specifics of these requirements. Visual standards, including textured surface standards, m
22、ay be used to supplement the drawing notes showing minimum acceptable appearance conditions. 5.Substrate PreparationThe substrate surface finish can affect the plated appearance. Suitable precautions in casting, forming, finishing, and cleaning must be taken to assure a satisfactorily finished plate
23、d part. Evidence of surface porosity, stress cracks, blisters, or other surface defects may indicate improper substrate preparation or inferior castings that may not have adequate durability after plating. The proper practices for preparing the zinc die casting for plating are discussed in ASTM B 25
24、2. SAE J1837 Issued JUN91 -3- 6.Design GuidelinesAn entire document could be written on “design guidelines“ and the reader is urged to consult a document such as ASTM B 507. 7.Metal FinishingBuffing or other mechanical treatments of the substrate, copper or nickel deposits are permitted provided tha
25、t minimum plating thickness, chromium microdiscontinuity, and other applicable requirements are met following these treatments. Buffing of the final chromium plate is not permitted as it will adversely affect corrosion resistance. 8.Plate Thickness 8.1The plate thicknesses listed in Table 1 shall be
26、 met on all areas of the significant surfaces. These thicknesses also apply to nonsignificant surfaces which, on corroding, may drip onto or otherwise affect a significant surface. a.Generally consists of a cyanide copper layer. It is up to the customer and supplier to agree on what type of copper o
27、r other plating process is utilized as the initial layer on zinc base parts. b.The copper layer may be plated from either a cyanide copper bath or an acid copper bath and it is up to the customer and supplier to agree on an acceptable plating bath. c.The use of a “high potential“ nickel layer (gener
28、ally 2.5 m or 0.0001 in thick) between the bright and semibright nickels can improve corrosion performance of the composite plate. The semibright nickel thickness may, therefore, be reduced by the thickness of the “high potential“ nickel layer if approved by the customer. d.If trivalent chromium is
29、employed, the minimum thickness shall be 0.50 m (0.00002 in). 8.2If, due to part geometry, the specified plating thickness on significant surfaces cannot be met, the customer and supplier shall agree on a minimum plate thickness or the use of an alternate coating method, e.g., auxiliary anodes. 8.3T
30、hickness MeasurementsThe thickness of the individual copper and nickel layers may be determined using the microscopic method, ASTM B 487, or the coulometric method, ASTM B 504. The nickel layers may also be measured using the “STEP“ test, ASTM B 764. Chromium thickness may be measured using ASTM B 5
31、04 or the spot test, ASTM B 556. In case of disputes, the microscopic method for measuring thickness shall be the referee method. TABLE 1PLATE THICKNESS Thickness, m (minimum)in (minimum) Copper Strike 5 (a) 0.0002 Copper 15 (b) 0.0006 Semibright Nickel 20 0.0008 Bright Nickel 10 (c) 0.0004 Total Se
32、mibright and Bright Nickel 30 0.0012 Microdiscontinuous Chromium 0.25 (d) 0.00001 SAE J1837 Issued JUN91 -4- 9.“Step“ Test Requirements 9.1ProcedureThe “STEP“ test shall be carried out in accordance with ASTM B 764. To obtain reliable and reproducible results, the following precautions should be adh
33、ered to: a.Prevent the reference electrode from drying out when not in use by keeping it immersed in either water, “STEP“ test electrolyte or dilute (5 to 10%) hydrochloric acid solution. b.Run sufficient verification tests on a primary or secondary standard to insure that the instrument is working
34、properly, before carrying out a test on an unknown sample. If the STEP value of the primary standard or secondary standard cannot be reproduced to within at least 5% of the reported value of the standard after three attempts, the instrument should be thoroughly checked for possible problems, e.g., p
35、late buildup on inside of cell, faulty reference electrode, miscalibrated chart recorder, etc. Primary standard test panels are available from the National Institute of Standards and Technology,1 while some instrument suppliers provide secondary standards. Tertiary standards may be actual parts or p
36、repared plated panels that have been calibrated against a primary or secondary standard. c.Keep plate buildup on the inside surfaces of the metal test cell to a minimum by frequent cleaning. d.Make sure the pH of the test electrolyte is 3.0 0.1 when preparing new solution or checking old solution. 9
37、.2Interpretation of Results a.The “STEP“ test may be used to measure the thickness of individual nickel layers when the instrument is properly calibrated. The thickness of the individual nickel layers shall meet the requirements of this document (See 8.1). b.Measurements should normally be made in l
38、ow to medium current density areas on significant surfaces whenever part geometry permits. The customer specified plating thickness check points are usually suitable locations for making “STEP“ test measurements. High current density areas of a part can be expected to exhibit values at least 15 to 2
39、0 mV greater than the low current density areas of the same part. c.At least two measurements should be made at any given test site and the average value reported. Test spots must not touch or overlap each other. The individual readings at any one site should not vary from each other by more than 10
40、%. Large variations suggest poor technique, faulty equipment, or defective deposits (e.g., cracks, pits, dirt inclusion, etc.). d.The millivolt “STEP“ potential difference between the various nickel layers shall be measured at the mid or low current density areas (See 9.2 b) and shall exhibit the re
41、lative values and activities listed as follows: 1.100 mV: Minimum difference between bright and semibright nickel layers with the bright nickel more active than the semibright. A difference of at least 125 mV is recommended as the statistical mean with values of 100 mV as the absolute minimum. Maxim
42、um values have yet to be determined, but generally should not exceed 200 mV. 2.20 mV: Minimum difference between the bright nickel and the high activity nickel strike (between the semibright and bright nickel) when one is present. The high activity nickel strike shall be more active than the bright
43、nickel layer. 3.20 mV: Maximum difference between the bright nickel and any subsequent nickel strike or microdiscontinuous nickel layer when one is present. This layer shall be less active than, or equal to, the activity of the bright nickel layer. 1.National Institute of Standards and Technology Of
44、fice of Standard Reference Materials, Room B-311 Chemistry Building, Gaithersburg, MD 20899. SAE J1837 Issued JUN91 -5- e.It is stressed that successfully meeting the “STEP“ requirements of this document without conforming to other deposit requirements, such as thickness, ductility, chromium microdi
45、scontinuity, CASS test, etc., may result in premature failure of the plated part in service. All the requirements of this document must be complied with to achieve maximum corrosion protection. 10.DuctilityTest Method: ASTM B 490 The ductility of the composite electrodeposit on the finished part is
46、considered acceptable when foils plated out of the individual nickel baths meet or exceed the following values: Semibright Nickel67% Bright Nickel11% NOTEA fully ductile individual nickel layer will have a foil test value 100% when computed using the formula D = 100 T/(2R-T). 11.Specifications for M
47、icrodiscontinuity 11.1 Determination of Microdiscontinuity and Active SitesDetermination of microdiscontinuity after chromium plate, and active sites after corrosion testing, shall be conducted as per ASTM B 456, Appendix X4. However, to determine active sites, the chromium layer in the area to be e
48、xamined shall be stripped using hydrochloric acid (concentrated), so that the corrosion sites in the nickel layer are more easily seen and counted. 11.2 Microdiscontinuity After Chromium PlateThere shall be a minimum of 10 000 pores/cm2 (64 000/in2). A maximum quantity of pores has not been establis
49、hed, but is dictated by visual acceptance, both before and after environmental testing, as agreed on between the customer and supplier. (The minimum number of cracks required when a trivalent chromium deposit is used, has not been established.) 11.3 Active Sites After Corrosion Testing (CASS)There shall be a minimum of 10 000 pores/cm2 (64 000/in2) after 22 h CASS test. The chromium deposit must be stripped off after the CASS test, but prior to counting and measuring the active sites. The active sites shall be