Electrogalvanized Coatings for Sheet Steel
|Publication Date:||1 October 2014|
This standard covers the requirements for both one and two side pure zinc and zinc nickel alloy electrogalvanized coatings. These coatings are applied to a sheet steel substrate utilizing an electroplating process. The sheet steel substrate may be either cold or hot rolled low carbon, rephosphorized, solid solution strengthened, bakehardenable, high strength low alloy, dual phase, complex phase, or martensitic 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), General 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.
Material Description. The type of coating, and its mass and finish are specified by suffixes added to the basic specification number. The first two letters EG will designate an electrogalvanized coating. The coating mass for each side is designated by a minimum value in g/m2. Only coating masses shown in Table 1 should be used unless materials engineering is consulted. Other coating masses shall follow the same designation method. For one side coated coils or sheets/blanks, a zinc residue of 40 mg/m2 maximum is permissible on the uncoated side. The letter G designates a pure zinc coating. The letter N designates a zinc-nickel alloy coating. The first set of digits along with the letter designation specifies the coating parameters of the unexposed side. The remaining designation specifies exposed (E), unexposed (U), or temper rolled (T) to depict surface finish.
Symbols. Not applicable.
Applicability. Sheet metal parts consisting of steel grades described by GMW2, GMW3032, or GMW3399.
Exposed (E). A finish produced by eliminating all visual spangle pattern and surface defects per 18.104.22.168, to be used for critical appearance applications.
Semi Exposed (Z). A spangle free finish produced by minimizing surface defects per 22.214.171.124 is used for secondary visible surfaces that do not require an exposed quality finish.
Unexposed (U). A minimum spangle finish used for non-critical appearance applications. See 126.96.36.199.
Temper Rolled (T). This surface shall have sufficient temper rolling such that Lüders lines or stretcher strain will not show when formed and painted. All other requirements are the same as U surface described above in 1.4.3.