Welding Reactive Metals

Beryllium has been welded with the gas tungsten arc welding process and with the gas metal arc welding process, and it is also joined by brazing. Beryllium should not be welded without expert technical assistance. Beryllium is a toxic metal and extra special precautions should be provided for proper ventilation and handling.
Zirconium and zirconium-tin alloys are ductile metals and can be prepared by conventional processes. Cleaning is extremely important and chemical cleaning is preferred over mechanical cleaning. Both the gas tungsten arc welding and the gas metal arc welding processes are used for joining zirconium. The inert gas chamber should be employed to maintain an efficient gas shield. Argon or argon-helium mixtures are used.

The zircalloys are alloys of zirconium which contain small amounts of tin, iron, and chromium. These alloys can be welded in the open in much the same manner as titanium. The electron beam process and the resistance welding processes have been used for joining zirconium.

The secret to the successful welding of titanium is cleanliness. Small amounts of contamination can render a titanium weld completely brittle. Contamination from grease, oils, paint, fingerprints, or dirt, etc., can have the same effect. If the material is cleaned thoroughly before welding and well protected during welding there is little difficulty in the welding of titanium.

The gas tungsten-arc and gas metal-arc welding processes can be used for welding titanium. Special procedures must be employed when using the gas-shielded welding processes. These special procedures include the use of large gas nozzles and trailing shields to shield the face of the weld from air. Backing bars that provide inert gas to shield the back of the welds from air are also used. Not only the molten weld metal, but the material heated above 1000°F (approx. 540°C) by the weld must be adequately shielded in order to prevent embrittlement.

When using the GTAW process a thoriated tungsten electrode should be used. The electrode size should be the smallest diameter that will carry the welding current. The electrode should be ground to a point. The electrode may extend 1-1/2 times its diameter beyond the end of the nozzle. Welding is done with direct current, electrode negative (straight polarity).

Selection of the filler metal will depend upon the titanium alloys being joined. When welding pure titanium, a pure titanium wire should be used. When welding a titanium alloy, the next lowest strength alloy should be employed as a filler wire. Due to the dilution which will take place during welding, the weld deposit will pick up the required strength. The same considerations are true when GMAW welding of titanium.

Argon is normally used with the gas-shielded process. For thicker metal use helium or a mixture of argon and helium. The purity of welding grade gases is satisfactory. They should have a dew point of minus 65°F (minus 54°C). Welding grade shielding gases are generally free from contamination; however, tests can be made before welding. A simple test is to make a bead on a piece of scrap, clean titanium, and notice its color. The bead should be shiny. Any discoloration of the surface indicates a contamination.

Extra gas shielding provides protection for the heated solid metal next to the weld metal. This shielding is provided by special trailing gas nozzles or by chill bars laid immediately next to the weld. Backup gas shielding should be provided to protect the underside of the weld joint. Protection of the backside of the joint can also be provided by placing chill bars in intimate contact with the backing strips. If the contact is close enough, backup shielding gas is not required. For critical applications use an inert gas welding chamber. These can either be flexible, rigid, or vacuum-purge chambers.

To guarantee that embrittlement of the weld will not occur, proper cleaning steps must be taken. Solvents containing chlorine should not be used. Recommended solvents would be tri-alcohol or acetone. Titanium can be ground with discs of aluminum oxide or silicon carbide. Wet grinding is preferred, however, if wet grinding cannot be used the grinding should be done slowly to avoid overheating the surface of the titanium.