ZnNi EG® Sheet
Introduction/Background:
ZnNi EG sheet consists of a homogeneous zinc-nickel alloy coating electrolytically deposited on a cold-rolled steel substrate using a continuous coil line process. The single phase composition range currently produced is typically 10-14% nickel by weight, the balance being zinc. The low-temperature coating application has no significant effect on the mechanical properties of the base metal, allowing a broad choice of steel grades.
Availability:
A variety of steel grades is available, including commercial quality, drawing quality, deep drawing quality and high-strength. Certain grades can be supplied as bake hardenable for enhanced dent resistance. ZnNi EG sheet sizes are summarized in Table 1.
Table 1. ZnNi EG® Sheet Size Availability1
| |
To 50 ksi (240MPa) minimum yield strength |
50-80 ksi (340-550MPa) minimum yield strength |
Thicknesses
in. (mm) |
0.020 (0.51)
0.065 (1.65) |
0.020 (0.51)
0.060 (1.53) |
Coil Widths
in. (mm) |
24 5/8 (625)
72 (1829) |
24 5/8 (625)
60 (1524) |
Cut Lengths
in. (mm) |
40 (1016)
240 (6096) |
40 (1016)
240 (6096) |
| 1. Maximum cross-sectional area 3.9 in.2 (2500mm2). Other limitations may apply within the ranges given. For sizes outside published limits - Please inquire. |
Coating masses range from 25 to 70 g/m2 (3.5 - 9.8 m m) per side.
For ZnNi coatings, the side-over-side coating mass designation is analogous to that outlined in ASTM Specification A879 for electroplated zinc coatings. For example, a zinc coating mass of 40 g/m2 per side would be specified as 40G40G. The same ZiNi coating mass distribution would be 40N40N.
® "EG" sheet is a registered trademark of Bethlehem Steel Corporation.
Our coating capabilities also include the application of organic coatings over ZnNi EG sheet in a one-pass operation. One such product is ZnNi-UC EG sheet (UC*, or Universal Coat, is an organic silicate topcoat). We are also continuing development on other composite organic coatings.
Corrosion Resistance:
Salt Spray: In the ASTM B117 salt spray test, ZnNi EG has shown advantages in both bare and painted conditions. Flat, unpainted panels with a coating mass of 30 g/m2 show 1% red rust at about 250 hours exposure. Test panels of electrogalvanized steels with equivalent coating mass were removed at 300 hours with 100% red rust. Considerable test-to-test variation from these averages can be expected, typical of salt spray testing. The improved performance of ZnNi EG is due to the increased barrier protection properties imparted by the nickel. Cut edge protection is slightly less than that of electrogalvanized coatings.
Tests of painted and scribed ZnNi EG sheet in salt spray resulted in 50-100% red rust in the scribe at 500 hours, and 1-4mm scribe creepback in both flat and deformed test configurations,from a painted edge was superior to pure zinc EG. These data, along with cold-rolled, are shown in Table 2.
Table 2. Cyclic Corrosion Performance (30 cycles)
| Substrate |
Unpainted Weight loss (g/m2) |
Painted Edge Creep (mm) |
| ZnNi EG
30N/30N |
514 |
0.3 |
| Electrogalvanized
60G/60G |
473 |
1.5 |
| Cold-Rolled |
1971 |
0.7 |
* UC is a trademark of NKK Corporation.
Formability:
ZnNi EG Sheet is a readily formable coated product. LDH min. values are comparable to those attained with electrogalvanized coatings. ZnNi EG sheet coating shows very little powdering and galling during forming operations. The coefficient of friction is typically 0.12-0.13.
Weldability:
The spot weldability of ZnNi EG sheet is excellent. Our testing has shown that even with higher coating thicknesses, ZnNi EG will generally give a minimum tip life of 9,000 welds. Weld current ranges are very similar to those of most zinc and zinc alloy-coated steel, as are the corresponding weld lobes.
Paintability:
The coating provides a highly paintable surface that accepts many standard pretreatments. It is also more forgiving of variations in pretreatments than electrogalvanized coatings. Like most electroplated coatings, the smoothness of the ZnNi EG coating is a function of the steel substrate surface, so it can be substituted for cold-rolled steel in critical, exposed applications without sacrificing appearance.
The low-temperature stone chipping resistance of ZnNi EG is excellent. The chipping resistance of all substrates in highly dependent on the pretreatment, primer and topcoats chosen. When all components of the paint system are optimized, ZnNi EG sheet shows superior performance.
Applications:
ZnNi EG Sheet should be considered wherever cold-rolled steel and electroplated zinc and other zinc alloys are currently utilized. The largest consumer of ZnNi-coated sheet is the automotive industry, where it is used for interior and exterior body panels, and painted trim elements. Because ZnNi EG sheet has excellent manufacturability, it can be used whenever a high-performance corrosion resistant sheet is required.
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