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Q: I would like to know what steps I need to take to properly weld zirconium, and what gas to use, pure argon or helium gas?

A: Welding of zirconium is commonly done with gas tungsten arc welding (Tig) or plasma arc welding (PAW) and is very similar in welding techniques to alloys such as titanium that are sensitive to oxidation when exposed to air at elevated temperatures.

The two critical issues to successfully weld zirconium are cleaning and gas shielding.

Since the strength and ductility are strongly affected by elements such as oxygen, nitrogen, hydrogen, carbon and iron, careful attention to cleaning both the base material and the filler metal is essential.

Wire brush the surface to be welded and surfaces adjacent to the weld joint with a clean wire brush prior to welding, and follow with an application of a non-chlorinated solvent or acetone with a clean, lint free cloth.

Once cleaned, the material should be welded within a short period of time to avoid recontamination of the surfaces. Additionally, the filler metal should be stored properly in sealed containers to avoid contamination.

Proper and complete gas shielding is essential.

All areas of the weld and surrounding zirconium should be protected with an inert gas shield, most commonly 100 percent argon, while above 600 degrees F to avoid oxidation. A gas lens, larger gas cups and extended trail shielding cups must be used. Proper back purging for pipe and back side protection for plate should be used as well where materials are exposed to temperatures greater than 600 degrees F during welding.

GTAW (Tig) welding with DC(-) polarity, using high frequency start only, along with either 100 percent argon (purity of 99.998 percent and dew point of -60 degrees F), 100 percent helium or a mixture of the two gases is acceptable.

Gas selection is based on the penetration requirements with helium or helium-rich blends with argon to yield greater penetration.

Tungsten selection would be the tungstens that are commonly-used for DC operation such as 2 percent thoriated tungsten, 2 percent ceriated tungsten, 1 percent lanthaniated tungsten, or 0.25 percent zirconated tungsten, ground to a pointed configuration.

As with most Tig welding applications, larger tungsten diameters allow the use of longer tungsten extensions that may allow for better visibility with the larger gas cones.

Minimize the distance from the gas cup to the part to minimize the potential for exposure of the arc to air. Flow of the gas should be set to minimize turbulence, and should be in the 30 cu.ft./hr. range.

When using filler metal, choose a filler that matches the grade of the zirconium that is being welded. There are three primary grades of filler metals: Er Zr2, used for UNS R60702; Er Zr3, used for UNS R60704; and Er Zr4 , used for UNS R60705.

The welding technique is similar to that used with stainless or titanium, and involves keeping the filler metal in the shielding gas to minimize the potential of oxidation of the filler metal, and “dabbing” the wire in the molten puddle.

These recommendations should embody the basic requirements for producing sound welds with zirconium.

These alloys require great attention to detail to be successful, and it can not be stressed enough to keep the materials clean and use appropriate shielding of all surfaces exposed to temperatures greater than 600 degrees F.

This column is sponsored by Penton and the Lincoln Electric Co., Cleveland. Dave Barton is a senior welding engineer in the Application Engineering Group of The Lincoln Electric Co. He oversees welding procedure development for both new technology and existing products, performs failure analyses for customers, and serves as a consultant on welding application problems. Barton has been with Lincoln Electric for 21 years. Send your questions for Mr. Barton in care of WDF by e-mail to: askdav@penton.com.