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Attachment 2: Welding Recommendations

General Comments: Hot-dipped galvanized sheets have been joined by welding processes for many years by modifying practices used for bare steel sheets.  Because of the light zinc coating weight applied to UPI.GalXC, the welding characteristics are closer to those of electro-galvanized and bare cold rolled sheets.

Process Recommendation: Where a welding process must be used in fabrication, projection welding is the preferred welding process for joining parts.  The direct spot welding process may also by used, series spot welding is not recommended because the shunting circuit results in excessive electrode heating.

Electrode Recommendation: For best surface appearance, use the RWMA Class 1 electrode.  For best electrode life, use the RWMA Class 2 electrode.  For the spot welding process, a truncated cone with an included angle of 120 degrees to 140 degrees should be selected.  The welding electrodes will require more frequent cleaning than that experienced when welding cold rolled sheet steel.  Maintaining an electrode cooling water flow rate of about two-gallons per minute is recommended to minimized cleaning frequency.

Welding Conditions: Using cold rolled sheets as a reference; weld time (cycles) must be increased by 10% or more, electrode force will require about a 5% to 10% increase, and post weld hold time should be increased slightly to insure best surface appearance.

Specific welder setups and more detailed information on welding zinc coated steel can be found in the American Welding Society Welding Handbook, or Volume 6 of the ASM Metals Handbook.
 

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Attachment 3:

Corrosion Testing of Low Coating Weight Zinc-Based Coatings

(UPI.GalXC vs. EGL)

Abstract

Sets of UPI.GalXC and electrogalvanized (EGL) panels were tested under salt spray conditions.  Panels of UPI.GalXC showed better resistance to the corrosive environment than the panels of electrogalvanized.

Introduction

Samples of UPI.GalXC and electrogalvanized were forwarded to U.S. Steel Technical Center for an evaluation of their corrosion behavior under salt spray testing.  The materials were evaluated for metallic coating weight and type, and surface chromium levels.  The materials were tested per ASTM B117 Salt Spray Specification.

Discussion

The characteristics and properties of the coatings is given in Table 1 (below).  The UPI.GalXC sample has a higher zinc coating and lower chromium coating than the electrogalvanized sample. (reported to be Usiminas EG with chromate from Brazil.)

Photographs of the samples after termination of test at 120 hours (5 days) in the salt fog environment are given in Figure 1.  The purpose of this testing was to run all of the panels to a uniform endpoint so that they could be compared directly to one another.  Panels are tested in triplicate to reduce possible anomalous behavior due to non-uniformity in either the samples themselves or in the test environment.  This very aggressive salt spray test readily shows differences between the materials.  The UPI.GalXC panels show some white rusting (zinc corrosion product) along with localized red rusting (iron-based corrosion products.)  The electrogalvanized panels shows almost complete red rust coverage.  Even with the slightly higher elevated chromium level of 2.1 mg/ft², the electrogalvanized panel set suffered the most extensive corrosive attack.

Conclusion

Of the materials tested, UPI.GalXC outperformed the electrogalvanized panels in the salt spray corrosion test of 120 hours (5 days).
 
 

Figure 1: Corrosion Samples after 120 hours in salt spray