Page 43 - MetalForming December 2019
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 metallics, are abbreviated as GA, HDGA or ZF. Electrogalvanized coatings are shown as EG, EGL or ZE. Other types of coatings used on steel for corrosion protection include an aluminum-sili- con (AS or AlSi) alloy commonly found in press hardening applications, and a zinc-aluminum-magnesium (ZAM or ZM) alloy now gaining in applications where cut-edge corrosion is a concern.
As for coating weights, G refers to pure zinc, as in the EG abbreviation for electrogalvanized or GI for hot-dip galvanized. The letter A refers to gal- vanneal, GA. The number either before or after this letter represents the coating weight. Syntax matters here. For exam- ple, the weight of a G60 coating differs from one designated as 60G.
A notation with the number first fol- lowed by G or A as a suffix describes the single-side coverage in g/m2. For exam- ple, a 60G coating signifies a minimum coverage of 60 grams of galvanized zinc on each square meter on each side of the steel. A notation such as 98G60G
indicates a minimum of 98 g/m2 of gal- vanized zinc on one surface and 60 g/m2 of galvanized zinc on the other surface.
Specifying G40, or any coating where the letter comes first, indicates a min- imum total zinc-coating coverage on both sides combined in oz./ft.2 divided by 100. For example, a G40 coating has a minimum total coating coverage of 0.40 oz./ft.2, or an average of 0.20 oz./ft.2 on each side.
Knowing the density of pure zinc, 446 lb./ft.3, allows for the conversion of the coating coverage to a thickness of 0.00034 in. per side, or 8.6 microns per side. Remember that only the total coverage must be 0.40 oz./ft.2, and it is reasonable to assume that each side will not measure exactly 0.20 oz./ft.2. To ensure sufficient corrosion protec- tion, the ASTM A653/653M specifica- tion also calls out a minimum single- side measurement as well. For G40, each individual side must measure at least 0.12 oz./ft.2, or slightly more than 5 microns. If this thickness isn’t suffi-
cient for the application, greater coat- ing coverage must be specified.
These differences in syntax mean that a 60G coating measures about the same as a G40 coating. The 60 g/m2 on one side equals 120 g/m2 combined top and bottom, which converts to 0.394 oz./ft.2, about equal to a G40 coating. As another example, a G60 coating weight signifies 0.30 oz./ft.2 of zinc on each surface, which approxi- mates a 90G coating weight.
In Europe, one or two letters (such as Z or ZF representing zinc or a zinc- iron-alloyed coating) followed by a num- ber represents the minimum total coat- ing mass combined on both surfaces expressed in g/m2. Using this notation, Z100 represents a hot-dipped galvanized zinc with a total of 100 g/m2 combined on both surfaces. In practice, the coating weight does not divide exactly evenly between the two surfaces.
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