1、 WORLDWIDE ENGINEERING STANDARDS Material Specification GMW8 Hot Dip Zinc Coatings for Sheet Steel Copyright 2013 General Motors Company All Rights Reserved November 2013 Page 1 of 9 1 Scope This standard covers the requirements for hot dip coatings, both galvanized and galvannealed, applied to a sh
2、eet steel substrate utilizing a continuous hot dip process. The substrate may be cold or hot rolled sheet steel. Additional requirements or agreements shall be specified by regional GM Automotive Operations business units (e.g., General Motors North America (GMNA), General Motors Europe (GME), Gener
3、al Motors South America (GMSA), Pan Asian Automotive Technical Center (PATAC) and General Motors Korea (GMK). Coated substrates per GMW14400 are not within the scope of this specification. 1.1 Material Description. The type of coating and its mass and finish are specified by suffixes added to the ba
4、sic specification number. The first two (2) letters HD, will designate a continuous hot dip coating. The coating mass for each side is designated by a minimum value in gram per square meter (g/m2). Only coating masses shown in Table 1 shall be used unless Materials Engineering is consulted. Other co
5、ating masses shall follow the same designation method. The letter G designates a pure zinc coating (galvanized) and the letter A designates a zinc/iron alloy (galvannealed) coating. The first set of digits along with the letter designation specifies the coating parameters of the unexposed side. The
6、remaining designation specifies E (exposed), Z (semi-exposed), U (unexposed), or T (temper-rolled). 1.2 Symbols. Not applicable. 1.3 Typical Applications. Sheet metal parts consisting of steel grades as described in GMW2, GMW3032 or GMW3399. 1.4 Remarks. Not applicable. 1.5 Finish Suffixes. 1.5.1 Ex
7、posed (E). A finish produced by eliminating all visual spangle pattern and surface defects per 3.1.3.3, to be used for critical appearance applications. 1.5.2 Semi-Exposed (Z). A spangle free finish produced by minimizing surface defects per 3.1.3.3 is used for secondary visible surfaces that do not
8、 require an exposed quality finish. 1.5.3 Unexposed (U). A minimum spangle finish used for non-critical appearance applications. See 3.1.3.3. 1.5.4 Temper Rolled (T). This surface shall have sufficient temper rolling such that luders lines or stretcher strain will not show when formed and painted. A
9、ll other requirements are the same as U surface described in 1.5.3. 2 References Note: Only the latest approved standards are applicable unless otherwise specified. 2.1 External Standards/Specifications. ISO 1460 ISO 7438 ISO/TS 16949 2.2 GM Standards/Specifications. GMW2 GMW3399 GMW15200 GMW16549 G
10、MW3011 GMW4795 GMW15425 GMW16823 GMW3032 GMW14057 GMW16170 GMW3059 GMW14058 GMW16546 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 GMW8 Co
11、pyright 2013 General Motors Company All Rights Reserved November 2013 Page 2 of 9 2.3 Additional References. GWS-5A Auto/Steel Partnership Weld Quality Test Method Manual (AZ-017-02295 1.0C RI) TMC003 Material Safety Data Sheet guidance documents (available at ). The following paragraph defines spe
12、cific requirements for material on delivery, processing, performance, and other stages during life cycle performance. Deviations required for individual GM business units are listed in the Deviations Section and shall be agreed upon between GM Purchasing and the supplier. 3 Requirements 3.1 Requirem
13、ents on Delivery. 3.1.1 Chemical Requirements. 3.1.1.1 Free Zinc Coatings. The coating produced shall consist of pure zinc and only minimum alloy layer. Pure zinc coatings may contain 75 ppm maximum cadmium and 100 ppm maximum lead, and must meet the requirements of GMW3059. The coatings shall not c
14、ontain trace elements that are detrimental to adhesive bondability, phosphateability or paintability. 3.1.1.2 Zinc-Iron Alloy Coatings. The coating is produced on a continuous hot dipped galvanizing line followed by a thermal treatment. The zinc-iron alloy shall be a completely alloyed coating. This
15、 product is not spangled and has the tendency to powder when severely formed. For this reason, the bulk iron content of the coating shall be 8% to 12% by mass, when tested per GMW4795 or other regionally accepted specification, in order to eliminate flaking problems. Zinc-iron coatings may contain 7
16、5 ppm maximum cadmium and 100 ppm maximum lead, and must meet the requirements of GMW3059. 3.1.1.3 Base Metal. The sheet steel base metal chemical composition shall conform to the requirements specified in GMW2, GMW3032, or GMW3399. 3.1.1.4 Surface Treatment. Products coated with a designated lubric
17、ant (e.g., mill oil or prelube) shall comply with GMW16546 and/or be approved by the local business unit. See the Deviations Section. 3.1.2 Mechanical Requirements. 3.1.2.1 Coating Bend Test. All bend tests shall be conducted in accordance with ISO 7438. For all steels supplied according to GMW2 and
18、 GMW3032 with 0.2% offset yield strength 500 MPa and all GMW3399 grades, the steel must be capable of a 90 degree test in any direction with a maximum test radius (r) related to the steel thickness (t) without flaking on the outside of the bend. Refer to Appendix A, Table A1 for maximum bend test ra
19、dii for each grade and a diagram of the test setup (Appendix A, Figure A1). For testing of all steels, flaking of the coating within 6 mm of the edge of the bend test shall not be cause for rejection. The specimens shall not be cut 25 mm from the coil edges of the test sheet. 3.1.2.2 Coated Base Met
20、al. The mechanical properties of the coated material in the as delivered condition shall conform to the requirements specified in the applicable GMW or industry substrate standards. 3.1.3 Physical Requirements. Coating mass and finish quality shall conform to the requirements prescribed in Table 1.
21、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 GMW8 Copyright 2013 General Motors Company All Rights Reserved November 2013 Page 3 of 9 Tab
22、le 1: Preferred Coatings and Coating Mass Requirements Note 1, Note 2 40G40G 50G50G 60G60G 70G70G 90G90G 45A45A 52A52A Exposed Coating Designation E E E E N/A E E Semi-exposed Coating Designation Note 3 Z Z Z Z Z N/A N/A Unexposed Coating Designation U U U U U U U Temper Roll T T T T T T T Minimum A
23、verage Coating Mass Each Side by Triple Spot Test (g/m2) 40 50 60 70 90 45 52 Maximum Average Coating Mass Each Side by Triple Spot Test (g/m2) 60 70 90 100 120 60 74 Minimum Coating Mass for any Individual Spot (g/m2) 34 43 50 60 75 40 45 Coating Thickness Each Side Note 1 Minimum/maximum (microns)
24、 by triple spot test: 5.6/8.5 7.0/9.9 8.5/12.7 9.9/14.1 12.7/16.9 6.3/8.5 7.3/10.4 Note 1: Coating thicknesses are shown for reference only, not for conformance to specification requirements. Note 2: Other coating masses may be used by exception. Refer to Deviations Section. Note 3: Semi-exposed des
25、ignation is not applicable for GME. N/A = Not applicable 3.1.3.1 Coating Mass. ISO 1460 shall be used for determination of coating mass of hot dip zinc coatings. Test sample size shall be 2000 mm2 minimum with a preferred sample size of 3330 mm2 (57.7 mm 0.1 mm square or 65.1 mm 0.1 mm in diameter).
26、 Coating mass shall be measured by triple spot test and must conform to the values in Table 1. The mass shall be the average of three (3) measurements taken across the width of the strip at least 25 mm from each edge. In no case shall the lowest value of any of the three (3) test samples fall below
27、the minimum individual spot requirement in Table 1. Each side should be measured separately to ensure that the requirements of Table 1 are met. 3.1.3.2 Coating Thickness. Coating thickness measurements may be used for routine quality control evaluations. Coating thickness shall be measured using a s
28、uitable layer thickness gauge, on-line x-ray gauge or from a specimen cut perpendicular to the panel surface. Suitable instruments for evaluation of coating thickness (e.g., Eddy current, ferromagnetic, or metallurgical microscope) shall have a capability of 1.0 m accuracy. When using a metallurgica
29、l microscope, standard mounting practices shall be used and thickness shall be measured at 1000x magnification. The referee method for determining coating thickness shall be coating mass, as specified in 3.1.3.1. For conversion between coating thickness and coating mass, the density factor of 7.1 g/
30、cm3 shall be used for pure zinc and zinc-iron alloy (galvannealed) coatings. 3.1.3.3 Coating Surface Quality. The steel shall be free from surface defects as negotiated between purchaser and supplier. For unexposed (U) surfaces defects such as, slight indentations, small marks, minor scratches, and
31、slight coloring, which do not affect corrosion resistance, formability or the application of surface coatings are allowed. Exposed (E) surface shall be free of defects which might affect the uniform appearance of quality paint or an electrolytic coating, electrodeposited primer (ELPO), cathodic e-co
32、at. Semi-exposed (Z) surfaces are spangle free and skin passed (temper rolled) to impart a higher degree of smoothness than is normal for as coated products. Certain applications require that both surfaces of the steel be of exposed (E) or semi-exposed (Z) surface quality. Temper rolling may be requ
33、ired and shall be specified with a (T) designation. The other surfaces shall conform at least to surface quality (U). Regulations in detail will be issued by the local business unit. 3.1.3.4 Surface Texture. Specific requirements for the texture for each region are detailed in GMW16823. Copyright Ge
34、neral 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 GMW8 Copyright 2013 General Motors Company All Rights Reserved November 2013 Page 4 of 9 3.1.4 Additiona
35、l Requirements. 3.1.4.1 Marking. Unless otherwise agreed at the time of ordering, marking shall be carried out on the unexposed surface of full finish coils for the outer panels and on the outer side of the coils for inner panels. The marking shall be agreed upon between the supplier and purchaser.
36、The ink used for marking shall be released by the purchaser. 3.1.4.2 Other Requirements. Requirements such as tolerances on product shape and dimensions, inspections units, number of tests, sampling, test conditions, retests, inspection documents, packing, and handling of disputes shall be agreed up
37、on between supplier and the local business unit. 3.2 Processing Requirements. 3.2.1 Additional Requirements. 3.2.1.1 Pre-Treatment Compatibility/Paint Adhesion. When tested with approved phosphate systems, zinc-based coated steels shall be capable of achieving a high quality zinc phosphate conversio
38、n coating according to GMW3011 (crystal size and coating weight). When tested with approved thin film pre-treatments, the requirements of GMW16170 (coating weight and thickness) must be fulfilled. Outdoor exposure and proving ground tests do not have to be performed for the qualification testing of
39、steels. 3.2.1.2 Welding. 3.2.1.2.1. Weldability. Sheet steel supplied to this standard shall be weldable with standard GM Weld Practices and meet spot weld, arc weld and laser weld acceptance criteria per GMW14057, GMW14058 and GMW15425, respectively. When required for qualification, testing for spo
40、t weldability shall be performed per GWS-5A and approved by the GM Manufacturing Engineering Weld Department. Contact the GM Weld Council for specific information regarding weldability at . 3.2.1.2.2 Pressure Welding Applications. Pre-coated flat products furnished to this specification shall be sui
41、table for resistance spot welding per the Auto/Steel Partnership Weld Quality Test Method Manual (AZ-017-02295 1.0C RI) and/or to GMW14057. If necessary, special measures shall be taken. 3.2.1.2.3 Fusion Welding Applications. Pre-coated flat products furnished to this specification shall be suitable
42、 for fusion welding as agreed upon by the supplier and purchaser and/or GMW14058. If necessary, special measures shall be taken. 3.2.1.3 Adhesive Compatibility. Coated steels supplied to this specification shall be capable of being bonded with GM approved adhesives when tested according to GMW16549.
43、 Testing to this specification will evaluate bonding characteristics to the metal surface. 3.2.1.4 Zinc-Iron Alloy Coating Powdering. Zinc-Iron Alloy (galvannealed) coated sheet steel shall be tested for excessive powdering as agreed upon between the purchaser and the supplier. 3.3 Requirements on O
44、ther Stages during Life Cycle. 3.3.1 Chemical Requirements. Provisions shall be made to prevent the addition of such elements (see 3.1.1) from scrap or other materials used in the manufacturing process which would impair the recyclability of the finished components. 4 Manufacturing Process Not appli
45、cable. 5 Rules and Regulations 5.1 Legal Regulations. All materials must satisfy applicable laws, rules, regulations and recommendations valid in the country of usage. 5.2 Language. In the event of conflict between the English and domestic language, the English language shall take precedence. 5.3 In
46、spection and Rejection. Samples of components or materials released to a GM material specification shall be tested for conformity with the requirements of this material specification and approved by the responsible Engineering department prior to commencement of delivery of bulk supplies. Copyright
47、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 GMW8 Copyright 2013 General Motors Company All Rights Reserved November 2013 Page 5 of 9 A new approva
48、l must be received for any changes, e.g., properties, manufacturing process, location of manufacture, etc. If not otherwise agreed, all testing and documentation normally required for initial release must be completed. It is the responsibility of the supplier to inform the customer in a timely manne
49、r, without solicitation, and to include documentation of all modifications of materials and/or processes and to apply for a new release. If not otherwise agreed, all release tests shall be repeated and documented by the supplier prior to commencement of delivery of non-conforming bulk supplies. In individual cases, a shorter test can be agreed to between the responsible Engineering department a
