Titanium Guide
Grades 2 and 5 (Ti-6Al-4V): properties, machining, anodizing and cost
Titanium combines the strength of steel at ~57% of its weight with outstanding corrosion resistance and biocompatibility. Grade 2 (commercially pure) is the formable, weldable workhorse; Grade 5 (Ti-6Al-4V) offers aerospace-grade strength (UTS ≈950 MPa) and is the most common alloy for machined components. The trade-off is cost and machining difficulty: low thermal conductivity and work-hardening demand careful process control.
1. Grades and properties
Commercially pure grades 1–4 differ in strength and formability; Grade 2 (UTS ≈344 MPa, yield ≈276 MPa) is the standard for sheet, pipe and chemical equipment. Ti-6Al-4V (Grade 5) reaches UTS ≈950 MPa with yield ≈880 MPa and ~14% elongation, density 4.43 g/cm³ and modulus ≈114 GPa.
Titanium is highly corrosion-resistant in seawater, chlorides and most acids, biocompatible for implants, and non-magnetic. Its specific strength (strength/density) beats steel and aluminum, which is why it dominates aerospace and high-performance motorsport.
2. Machining behavior
Titanium conducts heat poorly (~7 W/m·K vs 50+ for steel) and work-hardens: cutting generates high localized temperatures that weld chips to tools. Successful machining uses low speeds, high feed, copious coolant, sharp positive-rake tools and rigid setups — mirroring the practice for stainless but more extreme.
Standard tolerance of ±0.127 mm is readily achievable; precision features to ±0.025 mm are possible but tool wear increases cost. Surface finishes to Ra 0.8 µm are routine; grinding or polishing reaches Ra 0.2–0.4 µm.
3. Finishing and joining
Anodizing colors titanium electrolytically (gold, blue, purple, black) and can add wear resistance. Passivation, bead blasting and shot peening (for fatigue) are common; electropolishing gives a mirror finish. Coatings such as hard anodize or nitride are used for wear.
TIG welding is standard with inert gas shielding; weld zones are softer and lose some strength. Bolted assemblies should avoid galling — threads require anti-seize or lubricated assemblies, and titanium fasteners against titanium are prone to seizure.
4. Cost and selection
Titanium costs roughly 10–15× carbon steel and 5–8× aluminum per part for machined components; specify it only when weight, corrosion or biocompatibility justifies the premium. For extreme strength at minimum weight, Ti-6Al-4V is the reference material across aerospace and medical.
For cost control, minimize material removal (design near-net), avoid thin walls that chatter, and consolidate features to reduce setups. ASTM B265 (sheet), B348 (bar) and F136 (surgical implant) define supply specifications.
Quick reference
| Grade | UTS MPa | Yield MPa | Elong % | Density g/cm³ | Best for |
|---|---|---|---|---|---|
| Grade 2 (CP) | 344 | 276 | 20 | 4.51 | Chemical, sheet, marine |
| Grade 5 (Ti-6Al-4V) | 950 | 880 | 14 | 4.43 | Aerospace, medical, racing |
| Grade 23 (ELI) | 900 | 860 | 15 | 4.43 | Surgical implants |
| Ti-3Al-2.5V | 620 | 520 | 15 | 4.48 | Hydraulic tubing |
Sources & references
- ASTM B265 — Titanium sheet and plate
- ASTM B348 — Titanium bar
- ASTM F136 — Surgical implant Ti-6Al-4V ELI
- ISO 5832-3 — Implants, Ti-6Al-4V
- Xometry Learning Center — Titanium Guide (public engineering reference)