Can titanium be welded?
Yes. Ti-6Al-4V TIG welds well, but every surface above about 425 °C must be under argon: torch, trailing shield and back-purge. Judge the weld by its colour and work to AWS D17.1.
Titanium has no hardenability problem and no hot-cracking problem; Ti-6Al-4V welds are strong, ductile and, in the annealed condition, close to base-metal properties. The whole difficulty is contamination. Above roughly 425 °C (800 °F) titanium absorbs oxygen, nitrogen and hydrogen from the air, and those dissolve into the metal and embrittle it. A weld made with only torch shielding is brittle even if it looks sound. So the weld pool, the hot bead behind it and the root side all need argon: a large gas lens on the TIG torch, a trailing shield that follows the torch and covers the bead until it cools below the critical temperature, and a back-purge or an enclosed purge chamber for the root. Small or complex parts are welded inside a glove box filled with argon.
The colour of the finished bead is the inspection method. Bright silver means the shielding was complete; light straw and light blue are usually acceptable on non-critical work; dark blue, grey and white powdery oxide mean the weld is contaminated and must be removed. AWS D17.1 (aerospace fusion welding) is the governing spec and includes a colour acceptance table; ASME IX qualifies procedures for pressure work. Filler is matching ERTi-5 (AWS A5.16) for Ti-6Al-4V, or ERTi-5 ELI for the extra-low-interstitial grade. Commercially pure ERTi-2 filler is sometimes used for more ductile welds on non-structural parts.
Cleanliness before welding is as strict as shielding during it. Degrease with a solvent that leaves no residue, remove the alpha case from any surface that was hot-worked or heat treated in air, wipe the joint with a clean lint-free cloth, and wear clean gloves; fingerprints and cutting fluid cause porosity. Ti-6Al-4V is usually welded in the annealed condition and stress relieved afterwards at 480-650 °C (900-1200 °F) for 1-4 hours in vacuum or argon, which reduces distortion and restores some ductility. Solution-treated-and-aged (STA) material is not normally welded because the heat-affected zone loses its strength. Laser and electron-beam welding (the latter in vacuum) are common for thin and precise titanium parts and avoid the shielding problem entirely.
Welding for Ti-6Al-4V parts: where to send them
What to specify
- Base metal: Ti-6Al-4V annealed per AMS 4911 (sheet and plate) or AMS 4928 (bar), with ELI (AMS 4907 / 4930) for medical or fracture-critical parts
- Filler: ERTi-5 (or ERTi-5 ELI) per AWS A5.16
- Welding to AWS D17.1 with the weld class (A, B or C), and the colour acceptance limit (silver only for Class A)
- Shielding requirements: trailing shield, back-purge or purge chamber, and argon purity (99.995% minimum)
- Pre-weld cleaning: solvent degrease, alpha-case removal on any heat-treated surface, lint-free handling
- Post-weld stress relief in vacuum or argon at 480-650 °C (900-1200 °F), and the acceptable surface after it (no alpha case)
- Inspection: visual colour, dye penetrant, and radiography on Class A welds
Pitfalls
- Torch shielding only, with no trailing shield or back-purge; the bead turns blue or grey and is brittle
- Grinding titanium with wheels or belts used on steel; embedded iron causes porosity and corrosion
- Welding STA (solution treated and aged) material and losing the heat-affected zone strength
- Cutting fluid, fingerprints or tape residue on the joint causing porosity
- Stress relieving in an air furnace, which grows an alpha case that must then be machined or pickled off
- Judging a weld by its shape instead of its colour; a good-looking dark weld is a failed weld
Frequently asked questions
- What colour should a titanium weld be?
- Bright silver. That means the metal was shielded from air until it cooled. Light straw or light blue may be accepted on non-critical work per AWS D17.1; dark blue, grey or white oxide is contamination and the weld must be cut out.
- What filler is used for Ti-6Al-4V?
- ERTi-5 to AWS A5.16, the matching alloy, or ERTi-5 ELI for the extra-low-interstitial grade. ERTi-2 commercially pure filler gives a softer, more ductile weld for non-structural joints.
- Does welded titanium need heat treatment?
- A stress relief at 480-650 °C (900-1200 °F) in vacuum or argon is normal on Ti-6Al-4V weldments to reduce distortion and residual stress. It is not required for strength; the annealed alloy welds to near base-metal properties.
