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 entirelyvoluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefro
2、m, 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) 776-0243TO PLACE A DOCUMENT
3、 ORDER; (724) 776-4970 FAX: (724) 776-0790SAE WEB ADDRESS http:/www.sae.orgCopyright 1995 Society of Automotive Engineers, Inc.All rights reserved. Printed in U.S.A.SURFACEVEHICLE400 Commonwealth Drive, Warrendale, PA 15096-0001RECOMMENDEDPRACTICESubmitted for recognition as an American National Sta
4、ndardJ1755ISSUEDJAN95Issued 1995-01GUIDELINES FOR USAGE OF STAINLESS STEEL ANDBIMETAL FOR EXTERIOR AUTOMOTIVE BRIGHT TRIMForewordThis Document has not changed other than to put it into the new SAE Technical Standards BoardFormat.Stainless steel and bimetal have been used extensively for many years o
5、n automotive molding systems, as well asfunctional systems. These alloys provide an economical option for automotive trim systems. Bright moldings haveallowed designers to both enhance the appearance and differentiate models of the same platform.When choosing materials for moldings that are attached
6、 to the body, consider the whole system: component beingattached, method of attachment, location of the molding on the vehicle, and panel or structure to which the moldingis attached. All the materials must be compatible, to preclude galvanic corrosion or other destructive interactions.1. ScopeThe s
7、cope of this SAE Recommended Practice is to give guidelines for design, processing, andmaterial selection for stainless steel and bimetal exterior automotive moldings.2. References2.1 Applicable PublicationsThe following publications form a part of the specification to the extent specifiedherein. Un
8、less otherwise indicated the latest revision of SAE publications shall apply.2.1.1 SAE PUBLICATIONAvailable from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001.SAE J405Chemical Compositions of SAE Wrought Stainless Steels2.1.2 ALUMINUM ASSOCIATION PUBLICATIONAvailable from the Aluminum Assoc
9、iation, Inc., 900 19th Street, NW,Washington, DC 20006.Aluminum Standards and DataSAE J1755 Issued JAN95-2-3. Technical Requirements3.1 General Design Considerations3.1.1 CREVICE CORROSIONAvoid system designs that promote crevice corrosion, such as pockets or flathorizontal shelves that could collec
10、t corrosion promoting media. Crevice corrosion is intense localizedcorrosion that occurs in crevices or other shielded areas that are exposed to corrosive media. Stainless steelis susceptible to crevice corrosion. If possible, leave an open gap between the molding and the sheet metalto allow good ai
11、r circulation. Eliminate rough edges and minimize the effects of cold work on the edges tohelp make the molding less susceptible to crevice corrosion.3.1.2 CHROMIUM PLATINGChromium plated moldings have special shape requirements. Sharp corners andprojections are prone to excessive plating build-up a
12、nd/or burning, and therefore should be avoided. Deeprecesses, sharp radius concavities, and long return flanges tend to receive little or no plating, so those kindsof features should be avoided. To achieve uniform plating thickness, keep all appearance surfaces as closeas possible to the major plane
13、 of the part. Parts to be plated may need a hole in them for mounting on racks.3.1.3 GALVANIC CORROSIONStainless steel will cause galvanic corrosion of mild steel (galvanized or bare) oraluminum panels which it touches in the presence of an electrolyte, such as salt water. Therefore, stainlesssteel
14、should never be allowed to be grounded to the body. Do not count on the body paint to providesufficient isolation. When stainless steel in the vicinity of a paint chip or scratch is connected to the exposedmetal substrate via an electrolyte such as salt water, it will cause severe localized corrosio
15、n of the exposedmetal.The stainless steel can be isolated from the body by encapsulating the molding in plastic or using a foam orother nonconductive tape on the back. If the molding must be grounded to the body panel, then bimetalshould be used. Bimetal consists of stainless steel on the front side
16、, with aluminum clad on the back. Themolding is formed of this sandwich material. The aluminum on the back provides sacrificial protection for thebody. Note that when the aluminum corrodes, a white corrosion product forms which may bleed around ontothe front of the molding. This is most prevalent wh
17、en the molding edges are not curled around to the back.3.2 Fastening Considerations3.2.1 DESIGNDo not put holes in any body panel after paint! Even when holes are put in body panels beforepaint, they should only be put in “wet“ panels. Weld studs are preferred instead of fasteners that are insertedt
18、hrough holes.3.2.2 FASTENER MATERIALThe fastener material must be chosen carefully. Do not use stainless steel fastenersunless they touch only stainless steel, brass, and/or plastic. If the part is not too heavy, adhesives may beused. Plastic or coated aluminum fasteners may be used, depending on th
19、e molding material to which theyare attached. Steel fasteners must have corrosion protective coatings that are designed to resist the exteriorenvironment.If the moldings are solid stainless, they should not have any metal fasteners touching them (except stainlesssteel1). Plastic clips can be used to
20、 hold moldings to metal studs on the panel. Or adhesive foam tape maybe possible. If the stainless steel is partly encapsulated in plastic, metal fasteners may be used only in theplastic, and only if they do not go through a stainless steel core.1. If the screw goes into a brass or stainless steel n
21、ut that is isolated from the body, then it should be stainless or brass.SAE J1755 Issued JAN95-3-3.3 Processing Considerations3.3.1 SURFACE CONTAMINATIONIron abrasion can lead to red rust and potentially pit corrosion. During forming orother manufacture, it is important to avoid tool wear or other a
22、brasion that can contaminate the stainlesssurface. This is especially true if such tools have previously been used to process carbon steels or othermaterial.If such contamination is unavoidable, the stainless surface should be treated with diluted nitric acid or othersuitable cleanser with subsequen
23、t careful rinsing with water in order to reestablish the noncorrosivecharacter of the surface.3.3.2 SURFACE SMOOTHNESSThe smoother a stainless surface is, the easier it is to keep it clean. Brightannealing or buffing achieve such smoothness. Note that dust or other particles may adhere more easily t
24、oa materials horizontal (buffing) lines and can be drained off more easily from vertical (buffing) lines.3.3.3 SURFACE CLEANLINESSA mild detergent should be used regularly to clean the stainless surface. Frequentcleaning enhances appearance and long-term corrosion resistance of the stainless.3.4 Mat
25、erial SelectionRemember, only use stainless steel if it is insulated from the rest of the car! Bimetal(aluminum-backed stainless steel) is available for designs that cannot be isolated.3.4.1 STAINLESS STEEL (SAE J405)SAE 51434 is a chromium-molybdenum bearing alloy used where resistanceto pitting an
26、d rusting is required. It is used when roping control is not required for the product application.Roping becomes a concern on parts stretched more than 3 to 5%. SAE 51436 is similar to SAE 51434 incorrosion resistance. The addition of columbium allows its use when roping control is required for thep
27、roduct application. SAE 51434 and SAE 51436 do not need chromium plating to attain an acceptable,attractive appearance. However, chromium flashing will increase the corrosion resistance of SAE 51434 and51436. Note that those two alloys have had occurrences of pitting and red rust when used below the
28、 beltline.Generally, 0.10 to 0.12 m of chromium is recommended for achieving the additional corrosion protectionwithout causing a milky appearance. Buffing before chromium flashing may be needed to achieve the bestappearance.SAE 30201 is a chromium-manganese-nickel bearing alloy that is stronger, mo
29、re ductile, and has bettercorrosion resistance than SAE 51434 and 51436, unless parts are chromium flashed. It is sometimes usedfor automotive trim fabrication where increased ductility is required for deep drawing or where increasedatmospheric corrosion resistance is required. SAE 30301 is a chromi
30、um-nickel bearing alloy which hasgreater formability than the above alloys. It is used for trim parts requiring deep drawing or stretchingoperations or where increased atmospheric corrosion resistance is required. SAE 30201 and SAE 30301will appear yellowish unless they are chromium flashed or chrom
31、ium plated. The minimum thicknessrequirement for chromium flash is 0.12 m for color match.3.4.2 BIMETAL (SAE J405 FOR THE STAINLESS STEEL PORTION AND ALUMINUM STANDARDS AND DATA FOR THE ALUMI-NUM PORTION)Bimetal as used for exterior automotive trim consists of cold rolled SAE 51434 or SAE 30201stain
32、less steel metallurgically bonded to either an AA1100 or AA3003 aluminum alloy or an AA5052 alcladwith AA1100 series equivalent alloy. The stainless steel surface is intended to form the significant or visibleside of fabricated parts. The bimetal is to be comparable in appearance to solid stainless
33、steel and offersome corrosion protection to the vehicle due to the galvanic protection provided by the aluminum.The selection of which bimetal to use will be based more on formability than appearance. The formability isaffected by temper, aluminum alloy backing, and ratio of stainless steel thicknes
34、s to aluminum thickness.The supplier who will be forming the part should be consulted to help determine which choice of bimetalwould be most appropriate for a particular part.SAE J1755 Issued JAN95-4-As noted previously, the SAE 51434 alloy is susceptible to pitting and red rust when used below the
35、beltline.Therefore, chromium flash on the stainless steel side of the part may be needed for additional corrosionprotection. Follow the same guidelines as previously mentioned for SAE 51434 with chromium flash. Whenchromium flashing bimetal, one should run high current densities, and very short time
36、s in order to notdissolve too much aluminum in the chrome tank.3.4.3 NICKEL/CHROMIUM PLATINGFor a deeper chromium plating appearance, nickel/chromium plating can beused on any of the previously mentioned alloys. Different processing is used for SAE 51434 and SAE 51436than for SAE 30201 and SAE 30301
37、.PREPARED BY THE SAE STAINLESS STEEL AND BIMETAL SUBCOMMITTEE OF THE SAE BRIGHT TRIM COMMITTEESAE J1755 Issued JAN95RationaleNot applicable.Relationship of SAE Standard to ISO StandardNot applicable.ApplicationThe scope of this SAE Recommended Practice is to give guidelines for design, processing, andmaterial selection for stainless steel and bimetal exterior automotive moldings.Reference SectionSAE J405Chemical Compositions of SAE Wrought Stainless SteelsAluminum Standards and DataDeveloped by the SAE Stainless Steel and Bimetal SubcommitteeSponsored by the SAE Bright Trim Committee
