Titanium and its alloys demand the highest level of care during welding due to their extreme reactivity with atmospheric gases at elevated temperatures. Titanium begins absorbing oxygen, nitrogen, and hydrogen above 400°C — these contaminants severely degrade weld quality. This guide provides comprehensive titanium welding procedures for fabrication.
Why Titanium Welding Is Different
- Above 400°C: Titanium begins absorbing oxygen and nitrogen
- Above 535°C: Absorption rates increase dramatically
- Above 700°C: Titanium reacts violently with oxygen
- Molten titanium: Dissolves virtually any refractory oxide
Atmospheric contamination produces brittle, embrittled welds that may crack or show excessive hardness. Proper shielding is the single most important factor.
Welding Processes for Titanium
GTAW (TIG): Primary process. DCEN, 99.995% argon minimum, 2% ceriated tungsten. Gas lens strongly recommended for wider, more uniform gas coverage.
GMAW (MIG): For thicker sections (>6mm). Higher deposition rates but more challenging due to larger molten pool.
EBW (Electron Beam): Performed in vacuum, eliminating contamination entirely. Used for aerospace critical applications.
Laser Beam: Increasingly used for precision applications. Minimal HAZ and distortion. Requires excellent shielding gas coverage.
Shielding Gas System (Three Zones)
Zone 1: Primary Shield (Torch)
Gas lens recommended over collet body. Flow rate: 15-25 CFH through gas lens.
Zone 2: Trailing Shield
Extends gas coverage behind the torch to protect solidifying weld metal and HAZ as they cool below 400°C. Essential for titanium — weld remains contamination-sensitive until below ~315°C. Typically 150-300mm long, 10-20 CFH.
Zone 3: Backing Gas (Purge)
Root side must be protected with inert gas until below 400°C. Initial purge: 20-30 CFH. Maintenance: 3-5 CFH. Verify atmosphere below 50 ppm oxygen before striking the arc (20 ppm for critical applications).
Filler Metal Selection
| Base Alloy | Filler Metal | AWS Classification |
|---|---|---|
| Grade 1 (CP Ti) | Grade 1 | ERTi-1 |
| Grade 2 (CP Ti) | Grade 2 | ERTi-2 |
| Grade 5 (Ti-6Al-4V) | Grade 5 | ERTi-5 |
| Grade 7 (Ti-0.15Pd) | Grade 7 or 11 | ERTi-7 / ERTi-11 |
| Grade 9 (Ti-3Al-2.5V) | Grade 5 or 12 | ERTi-5 / ERTi-12 |
| Grade 12 | Grade 12 | ERTi-12 |
Store filler metal in sealed container with desiccant. Clean with acetone before use. Handle with clean gloves.
Cleaning Procedures
- Degreasing: Clean with solvent (acetone, IPA) using lint-free wipes. Remove all oils, grease, cutting fluids.
- Mechanical cleaning: Stainless steel wire brush (dedicated for titanium only) or grinding with dedicated wheels.
- Final cleaning: Acetone-dampened lint-free cloth immediately before welding. Must weld within 4 hours or repeat process.
Weld Quality Indicators (Color Chart)
| Color | Interpretation | Action |
|---|---|---|
| Bright silver/straw | Excellent shielding | Accept |
| Light gold/bronze | Good shielding | Acceptable |
| Dark blue/purple | Moderate contamination | Marginal — review shielding |
| Dark blue with chalky white | Significant contamination | Reject |
| Yellow/grey/white powder | Severe contamination | Reject — stop welding |
Common Weld Defects
Porosity: Caused by contamination (hydrogen, moisture, oil). Improve cleaning, verify gas purity, check for leaks.
Cracking: Usually from excessive oxygen/nitrogen contamination. Improve shielding, verify base metal certification.
Tungsten inclusion: From electrode-pool contact. Maintain proper arc length.
Standards and Codes
- AWS D1.9/D1.9M: Structural Welding Code — Titanium
- AMS 2680: Welding titanium and titanium alloys
- ASME Section IX: Welding procedure and performance qualification — includes titanium
Summary
Titanium welding demands meticulous attention to shielding gas coverage, surface cleanliness, and process control. With proper procedures — three-zone gas shielding, dedicated cleaning protocols, and appropriate filler metal selection — high-quality titanium welds can be achieved consistently.
CoreMetal Steel supplies titanium sheet, plate, pipe, and bar in commercially pure (Grade 1-4) and alloy (Grade 5/Ti-6Al-4V) conditions, certified to ASTM and AMS standards.