Hot Dip Zinc Coatings for Sheet Steel
|Publication Date:||1 March 2019|
This standard covers the requirements for hot dip coatings, both galvanized and galvannealed, applied to a sheet steel substrate utilizing a continuous hot dip process. The substrate may be cold or hot rolled sheet steel specified per GMW2, GMW3032, GMW3399, or GMW17627. Additional requirements or agreements shall be specified by regional GM business units. 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 (2) letters will designate a continuous hot dip (HD) 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 coating 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 remaining designation specifies E (exposed), Z (semi-exposed), U (unexposed), or T (temper-rolled).
Symbols. Not applicable.
Applicability. Sheet metal parts consisting of steel grades as described in GMW2, GMW3032, GMW3399, or GMW17627.
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 Luders Lines or stretcher strain will not show when formed and painted. All other requirements are the same as U surface described in 1.4.3.