1、 WORLDWIDE ENGINEERING STANDARDS Material Specification GMW3044 Zinc Plating Copyright 2012 General Motors Company All Rights Reserved February 2012 Originating Department: North American Engineering Standards Page 1 of 6 1 Scope This specification covers the basic requirements for electroplated zin
2、c applied to fasteners, clips, and small and medium-sized ferrous parts, such as castings and stampings. This specification also provides for plating thickness, use or non-use of supplementary treatments and corrosion and for mechanical plating. MATSPC approvals for this finish are specific to the p
3、ost-supplementary treatment (suffix) evaluated for initial chemical/applicator approval (reference Section 6). The use of this specification to plate other parts, including, but not limited to, stampings or roll-formed parts for body or chassis applications must be reviewed and approved by the respo
4、nsible materials engineering organization. 1.1 Material Description. This coating system must be free of hexavalent chromium, per GMW3059 requirements. The plating shall be shown on the part drawing. Table 1 lists the common plating thickness codes covered by this specification. It is recommended to
5、 use these common codes to avoid product complexity. This plating is at present approved in clear (bright) color only. Black color (passivation product) as shown in Table 1 is not approved yet. Any other colors (where color is developed by adding pigment), if required, do not need a specially approv
6、ed source for the color. Establish availability at one of the sources approved to the required post-supplementary code (suffix) before putting any color other than clear (Bright) on the drawing. 1.2 Symbols. Not applicable. 1.3 Typical Applications. Zinc plating is typically applied on small- to med
7、ium-sized ferrous parts such as castings, fasteners, stampings, and clips. 1.3.1 Zinc-plated parts or their corrosion products must not come in contact with stressed polyamides 6 or 66. 1.3.2 Zinc-plating types without supplementary treatment are also used as a basecoat for an additional paint. This
8、 coating must be so applied that no negative influence in appearance and adhesion appears (e.g., blistering by effusion of hydrogen). 1.4 Remarks. Not applicable. 2 References Note: Only the latest approved standards are applicable unless otherwise specified. 2.1 External Standards/Specifications. A
9、STM E140 ISO 16047 ASTM F1470 SAE/USCAR-5 DIN 946 SAE/USCAR-7 ISO 1463 SAE/USCAR-11 ISO 9227 2.2 GM Standards/Specifications. 9984094 GMW14573 9985490 GMW14657 GMW3059 2.3 Additional References. TMC003 Material Safety Data Sheet guidance documents (available at ). GM Global Fastener Catalog (availab
10、le at ). 3 Requirements 3.1 Appearance. The as-received appearance and color hue shall be as agreed upon between the purchaser and supplier using approved color and hue engineering standards when available. In the case of zinc plus passivation coating listed herein, a clean, commercial finish is req
11、uired; range of color, iridescence, opaqueness, and sheen are normally not critical unless otherwise specified by the purchaser. In the case of bright zinc plus clear finishes listed herein, a clear bright appearance (also referred to as colorless, blue-bright and clear silver-white) is required. Sp
12、ecified colors shall be uniform, tightly adherent, hard and dry. 3.2 Plate Thickness. Thickness of plate shall be no less than the values shown in Table 1 or as designated for the suffix specified by Product Engineering. Such values are intended to apply to significant surfaces as specified on engin
13、eering drawings. In the case of finishes with Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW3044 Copyright 2012 General Motors Company
14、All Rights Reserved February 2012 Page 2 of 6 supplementary treatment, color, etc., the values shown apply to the thickness of plate after treatment. Supplementary treatments such as oils, waxes or other specified coatings are not applicable to thickness measurements. The plating thickness on bolts
15、and screws shall be measured on the head and the thread tip; on nuts it shall be measured on the spanner flats. 3.2.1 The thickness of the plated finish shall be determined by microscopic examination of cross-sections taken perpendicular to significant surfaces or by other methods agreed upon by the
16、 supplier and purchaser. For recommended practice for measuring thickness of electrodeposits, see ISO 1463. 3.2.2 The maximum allowable thickness of the plating on threaded fasteners shall be twice the minimum specified plating thickness. The maximum thickness of plating, which may be applied to thr
17、eads on threaded products, is limited by the basic thread size (tolerance “h” or “H”). After coating, parts must gauge with appropriate basic size Go thread gauge. Threads may be produced undersize or oversize (before coating) to accommodate the coating thickness, providing the finished product (aft
18、er coating) meets all specified mechanical properties. Where mechanical properties are not specified, undersizing or oversizing is subject to approval by the pertinent engineer, and all undersizing or oversizing shall be within permissible limits as agreed upon. 3.2.3 The allowable variation of maxi
19、mum plating thickness in the case of non-fasteners could be more than twice the minimum specified plating thickness, as long as it shall not affect the function of the part. Note: In special cases, such as welding applications, limiting the maximum plating thickness to a specific requirement shall b
20、e noted on the engineering drawing. 3.3 Adhesion. The coating shall have good adhesion to the base material. There shall be no blistering or flaking of the finish, including after any heat-treatment, as follows: The adhesion in the as-received conditions shall be checked as follows: Expose coated pa
21、rts to 220 5 C for 30 5 minutes and quench in water at room temperature. After quenching in water, blistering and/or chipping is not allowed. Electrolytically coated components produced from aqueous solutions must satisfy the mechanical property requirements of the uncoated parts. 3.4 Corrosion Resi
22、stance. Parts plated to these specifications shall be capable of withstanding Neutral Salt Spray (NSS) testing for the minimum number of hours shown in Table 1 or as designated for the suffix specified by the purchaser. 3.4.1 Parts must be tested to ISO 9227 to meet the corrosion resistance requirem
23、ents on significant surfaces per 3.4.4 and 3.4.5 for initial approval of the finish, applicator and Production Part Approval Process (PPAP) submissions. 3.4.2 For the normal production process, the NSS test shall be part of the applicators statistical process control to ensure that parts meet the co
24、rrosion resistance requirements. 3.4.3 The applicator shall run a periodic NSS test of the parts in process on each line running this coating, with sample size of three pieces minimum per shift per line. Based upon the chemical manufacturers instructions, the actual processing control checks shall b
25、e made and recorded. The supplier shall maintain the test results in a file to be submitted when required by GM, unless otherwise agreed between the purchaser and supplier. 3.4.4 Significant surfaces for test evaluation of fasteners shall be all exposed surfaces of the fastener when installed, inclu
26、ding but not limited to fastener heads, socket recess, SEMS washers and external surface of nuts. Fastener threads and point are excluded unless otherwise specified on the drawing. 3.4.5 Significant surfaces on parts other than threaded fasteners shall be all surfaces. Deep recesses, such as blind h
27、oles and the interior of tubes are excluded unless otherwise specified on the drawing. 3.4.6 In the case of finishes involving supplementary treatment, parts shall be aged at the ambient laboratory temperatures for at least 24 h before the test. In some cases, a heat treatment 1 h 5 minutes at 150 5
28、 C may be required prior to NSS testing. When such treatment is necessary, it shall be specified on the part drawing by using an “H” in the plating suffix as shown in Section 8 of this specification. In this case, the finish shall meet the corrosion resistance requirements before and after heat trea
29、tment. 3.4.7 When evaluation of zinc corrosion products is specified, acceptable resistance is defined as no white corrosion products on significant surfaces after exposure to NSS for the number of hours shown. 3.4.8 Except for black, color-dyed, bright, light iridescent blue and clear coatings, the
30、 degree of color change after salt spray test is not a significant Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW3044 Copyright 2012 Ge
31、neral Motors Company All Rights Reserved February 2012 Page 3 of 6 parameter unless otherwise agreed upon by the purchaser and supplier. Table 1: Zinc Plating and Related Finishes Code to Specification Number Note 1 Minimum Plating Thickness (m) Note 2 Supplementary Treatment Note 3 Typical Appearan
32、ce Note 4 Neutral Salt Spray, h Note 5 Base Metal Corrosion Zinc Corrosion Product Note 6 3U24/0 3 None No Requirement 24 6U48/0 6 48 9U72/0 9 72 12U96/0 12 96 15U120/0 15 120 6K96/48 6 Passivation/ Conversion Coating Clear (Bright) 96 48 8K240/120 8 240 120 15K360/120 15 360 120 8B240/120 8 Passiva
33、tion/ Conversion Coating Black 240 120 Note: Other codes are possible in special cases, e.g.,11K360/120, and may be devised as per the guidelines in 1.1. Establish availability before creating special codes. Note 1: Where a mechanical (peen) plating is required in lieu of electroplating, the letter
34、“M” is added to the code in the position immediately following the thickness number, e.g., GMW3044 6MU48/0. Note 2: See 3.2.2 and 3.2.3 for maximum thickness requirements. Any deviation for the plating thickness requirements can be shown on the drawing of the part. Note 3: Further supplementary trea
35、tments such as oil, wax or other coatings, if required, are specified on the drawing as suffix “Y”. Any changes that affect corrosion properties shall be negotiated between the purchaser and supplier. Note 4: Clear (Bright) and Black colors are available. Establish availability before putting any co
36、lor other than Clear (Bright) and Black on a drawing. Unless other color is specified, the supplier will process the parts in Clear (Bright) color. Note 5: When the finish is to be heat-treated prior to salt spray testing, the letter “H” shall be shown as the last character of the plating code, e.g.
37、, GMW3044 8K240/120XH. Samples shall be heat-treated for 1 h 5 minutes at +150 5 C. Note 6: Codes that specify more than 48 h before zinc corrosion products may require special handling. The suffixes “T”, “X”, “Y”, “G”, or “N” when added to the plating code indicate the application of post-treatment
38、 materials as described in 3.6. Example: 8K240/120X. 3.5 Hydrogen Embrittlement. Fasteners heat-treated or highly cold-worked to the specified core hardness greater than HRC 32 (HV320) or surface hardness HV 353, which are processed through the hydrogen-generating processes shall be processed per SA
39、E/USCAR-5 and tested for de-embrittlement per SAE/USCAR-7. The sample size for the SAE/USCAR-7 test shall be per ASTM F1470. High-strength ferrous steel parts formed from steel sheet or strip that are not surface hardened shall be processed through the SAE/USCAR-5 bake cycle specified for materials
40、that have a hardness of HV 353 or higher and shall be baked after plating within the time limits specified by that specification. A converted hardness per ASTM E140 is acceptable based on acceptance of the purchaser and supplier. 3.5.1 When supplementary treatment is specified for a part that requir
41、es baking after plating, the supplementary treatment shall be applied after the baking operation. 3.6 Processing Requirements. For certain fastener applications, a post-treatment of the electrolytically coated components - with or without passivation - may be necessary, using lubricants, waxes, dipp
42、ing solutions or other materials. In this case, the following suffixes apply: T: Dipping solution with or without lubrication. If without integrated lubrication, an additional Copyright General Motors Company Provided by IHS under license with General Motors CompanyNot for ResaleNo reproduction or n
43、etworking permitted without license from IHS-,-,-GM WORLDWIDE ENGINEERING STANDARDS GMW3044 Copyright 2012 General Motors Company All Rights Reserved February 2012 Page 4 of 6 lubricant must be used, coefficient of friction 0.13 0.03 (6 sigma). This suffix is to be used on fasteners of special appli
44、cations to meet 3.7, 3.8 and 3.9 requirements. X: With dipping solution only. G: Dipping solution with or without lubrication. If without integrated lubrication, an additional lubricant must have a coefficient of friction 0.13 0.03 (6 sigma). This suffix is to be used on general fasteners to meet th
45、e basic torque-tension/coefficient of friction requirements per 3.7 and 3.8. Y: Other material, as specified on drawing. “Y” suffix could be used along with other suffix in a code if required (example: GMW3044 8K 240/120NY, then describe “Y” on the drawing). N: Without any dipping solution, lubrican
46、t, or any chemicals applied. Note: If no suffix to the code is used, the provision of suffix “N” shall apply. 3.6.1 All these treatments shall not reduce the corrosion protection of the finish. 3.7 Torque-Tension Test. For bolts and nuts which are post-treated to suffixes “G” and “T”, M10 x 1.5 surr
47、ogate bolts shall be processed with the production parts. A minimum of ten bolts per finish line per shift shall be tested per SAE/USCAR-11, except tightening speed shall be 30 3 RPM and test parts as shown in Table 2. The 6 sigma torque value must be within the listed range (Table 2). The test resu
48、lts shall be maintained in the file to be submitted when required by GM. Table 2: Test Parts Thread Size Surrogate Bolt Part Number Test Nut Part Number Test Washer Part Number Torque (Nm) Tension (kN) Suffixes M10 x 1.5 11516105 11516090 11502644 48 8 28.3 T and G Note: Engineering drawings for sta
49、ndard GM general fasteners can be found on Supply Power under GM Global Fastener Catalog. Standard test materials for laboratory testing of fasteners can be produced through a qualified fastener supplier meeting the test part drawing. 3.8 Coefficient of Friction. For fasteners, which are post-treated to suffixes “G” and “T”, the coefficient of friction of the threaded fasteners tested per ISO 16047 shall be 0.1
