Titanium Grade 5 (Ti-6Al-4V) is the most widely used titanium alloy, accounting for over 50% of all titanium production. Its exceptional strength-to-weight ratio makes it essential in aerospace, medical implants, and high-performance motorsport — but welding it demands rigorous gas shielding and cleanliness protocols.
Why Titanium Welding Is Different
Above 500°C, titanium reacts aggressively with oxygen, nitrogen, and hydrogen in the atmosphere. These elements dissolve interstitially in the crystal lattice, causing embrittlement and catastrophic loss of ductility. A properly shielded titanium weld is bright silver; blue or straw coloration indicates minor contamination, while white or flaky oxide indicates severe contamination requiring removal and re-welding.
Gas Shielding Requirements
Titanium welding requires three distinct shielding zones operating simultaneously:
- **Primary shield**: Standard torch nozzle with 99.999% pure argon at 12–15 l/min. Use a gas lens for laminar flow.\n- **Trailing shield**: Custom trailing device covering 150–200 mm behind the weld pool until the metal cools below 425°C. Flow rate 15–25 l/min.\n- **Back purge**: Fully sealed back purge with argon until oxygen content drops below 50 ppm, verified by an oxygen analyzer. Flow rate 10–20 l/min.
All gas lines must use high-purity regulators with stainless steel or PTFE tubing. Standard rubber hoses will contaminate the gas supply. Pre-flow time should be minimum 15 seconds; post-flow minimum 30 seconds.
Joint Preparation and Cleanliness
Surface preparation is critical. All surfaces within 25 mm of the weld must be cleaned with acetone or isopropyl alcohol (never chlorinated solvents — they cause stress corrosion cracking). Use only dedicated stainless steel wire brushes and carbide burrs that have never contacted other metals.
Fit-up must be precise with minimal gaps. Root gaps exceeding 10% of material thickness significantly increase the risk of porosity and oxygen pickup. Tack welds must be made with full shielding — contaminated tacks must be ground out completely.
Welding Parameters for GTAW
GTAW (TIG) is the primary process for titanium. Parameters for Grade 5 Ti-6Al-4V:
- **2 mm sheet**: 60–80 A, 10–12 V, DCEN, 1.6 mm filler (ERTi-5)\n- **3 mm plate**: 90–120 A, 11–13 V, DCEN, 2.4 mm filler\n- **6 mm plate**: 140–180 A, 12–14 V, DCEN, 2.4–3.2 mm filler (multi-pass)\n- **10 mm plate**: 160–200 A, 12–15 V, DCEN, 3.2 mm filler (multi-pass)
Travel speed should be moderate — too fast causes insufficient shielding coverage; too slow causes excessive heat input and grain growth. Interpass temperature must not exceed 175°C.
Post-Weld Inspection
Visual inspection is the first indicator: bright silver is acceptable, light straw may be acceptable for non-critical applications, blue indicates contamination, and white/flaky oxide requires rejection and re-work.
For critical applications, perform dye penetrant testing per ASTM E165, radiographic testing per ASTM E1742, and hardness testing (contaminated welds show significantly elevated hardness above 370 HV). Bend testing per AWS D17.1 verifies ductility — contaminated welds will crack during bending.
Common Mistakes to Avoid
- **Inadequate trailing shield**: The most common cause of weld discoloration. Invest in a proper trailing shield device.\n- **Contaminated filler wire**: Store titanium filler in sealed bags with desiccant. Handle only with clean nitrile gloves.\n- **Grinding with aluminum oxide wheels**: Use only silicon carbide or diamond wheels. Aluminum oxide embeds in titanium and creates hard spots.\n- **Insufficient back purge verification**: Always use an oxygen analyzer — visual inspection of back-purge quality is unreliable.