Sparrows Point:Galvalume Technical Bulletins

Galvalume sheet is used in many applications that require resistance and arc welding techniques in their fabrication. Utilizing conventional welding techniques along with the guidelines given below, Galvalume sheet can be as easily welded as other coated sheet products. In general, the Al/Zn coating is soft and conductive compared to uncoated sheet steel and, therefore, requires higher welding currents, welding times and electrode forces for resistance welding. The parameters used for successfully welding Galvalume sheet are very similar to those for galvanized sheet.

The optimum tip geometry which provides the longest electrode tip life when spot welding Galvalume sheet is the truncated cone with either a 90� or 120� included angle. Pointed, domed or radius electrodes should be used only where necessary for reasons of access or alignment.

Bethlehem's testing has shown that a dispersion-strengthened copper alloy electrode will provide superior electrode life and welding characteristics when compared to RWMA Class 2 Cu-Cr or Cu-Zr alloys. One commercially available, dispersion-strengthened alloy is "Nitrode" from The Nippert Company, 801 Pittsburgh Drive, Delaware, OH, 43015, (614) 363-1981.

Material Thickness (in.)	Welding Current (amperes)	Electrode Force (lb)	Welding Time, Cycles (1/60 second)	Electrode Face Diameter(in.)
0.022	11,000	350	10	0.187
0.028	11,300	400	12	0.187
0.036	12,500	500	14	0.250
0.040	12,800	500	14	0.250
0.053	13,000	550	14	0.250
0.065	13,400	650	18	0.250

Electrode maintenance is also important in spot welding coated sheet steels. The parameters given above will cause gradual deformation of the contact surfaces as well as coating alloying with the electrode material. These factors require that the electrodes be redressed more frequently than is the case with uncoated steel. In general, the electrode tips should be redressed periodically, but the time between redressings depends on the sheet thickness and conditions of use. Additional factors influencing electrode life are proper tip alignment and sufficient water cooling (minimum 2 gal./min.) to the electrode.

The peel test, which is commonly used as a measure of nugget size and weld soundness, can be used to test the quality of spot welds on Galvalume sheet. Test specifications vary among manufacturers, but in general, two coupons are welded together and then peeled apart. Under proper welding conditions, failure should occur around the weld, not through the weld. The nugget diameter should approximate the diameter of the electrodes.

The conditions for seam welding Galvalume sheet are similar to those for galvanized steels in that higher currents and closer control of welding schedules are required than for uncoated sheet steel. Intermittent current feed is preferred over continuous current and 0.5-inch radius faced electrodes can be used for all sheet thicknesses if desired. Schedules for seam welding Galvalume sheet are suggested below:

Material Thickness(in.)	Electrode Face Type	Electrode Thickness (in.)	Electrode Force (b)	Welding Current (amperes)	Weld Times,Cycles		Welding Speeds (in./min)
					Heat	Coat
0.017	1/2" Radius	3/8	700	14,500	2	2	60
0.022	1/2" Radius	3/8	850	16,000	3	2	60
0.034	1/4" Flat	1/2	1000	21,500	4	2	60
0.049	1/4" Flat	1/2	1100	22,000	4	2	60
0.049	1/4" Flat	1/2	1100	23,000	4	1	90
0.083	5/16" Flat	3/8	1600	27,000	10	6	30

As with the spot welding schedules, the conditions above may need alteration depending on the job.

Seam welding wheels should be RWMA Class 2 copper alloy. Knurled wheels are preferred because the knurled drive rollers continuously remove pick-up from the sheet coating and maintain a constant face width, thus eliminating the need for redressing. The electrode wheels in the weld area should be flushed with water during welding to provide adequate cooling.

Galvalume sheet has been fabricated into products such as tubing using both high-frequency and low-frequency welding techniques. Standard procedures similar to those employed for galvanized or aluminum-coated steels are used. Since the coating may smear at sheared or slit edges, it may be necessary to scrape the sheet edges prior to welding.

Gas tungsten-arc (TIG) welding of Galvalume sheet is not recommended because, as with galvanized sheet steel, fumes generated during welding tend to contaminate the tungsten electrode and cause instability of the arc.

Shielded metal-arc welding is best accomplished using E60XX electrodes, such as E6010, E6011 or E6012. A whipping technique is often used to burn off the coating ahead of the weld puddle.

For gas metal-arc (MIG) welding, a mild steel wire should be used with Ar/1% O2 or Ar/CO2 shielding gas. Gas containing Ar provides a more stable arc resulting in better bead appearance and significantly less weld spatter. When a backup plate is used, the plate should be grooved under the weld to provide better penetration and venting of fumes from the underside of the weld.

In arc welding, the total weight of evolved fumes per unit weld area for Galvalume sheet is 25 percent of the amount for galvanized. The ratio of the amount of zinc oxide released from Galvalume sheet is only 20 percent of that released from galvanized sheet. The decreased fuming of Galvalume sheet represents a reduced fume hazard to welders, but the extent of fuming is still sufficient to require the use of fume hoods and/or forced exhaust systems.

Fuming during resistance welding is very slight and special exhaust systems should not be needed.

As is the case with other coated sheet steels, spot and seam welding may remove the coating from Galvalume sheet exposing the base steel. These areas may be too large to be galvanically protected by the adjacent coating and should be covered with metal-sprayed zinc or aluminum, zinc-rich paint or organic coatings. Covering the weld area of arc welds is especially important because the damage to the coating is even more severe. See Bethlehem's Technical Bulletin TB-200 for more information on techniques and materials for field painting Galvalume sheet. Metco, Inc., 1101 Prospect Avenue, Westbury, NY, 11590, (516) 334-1300, can provide guidelines and equipment for metal spray applications

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