Ti-6Al-4V Titanium (Grade 5)
Also: Ti-6Al-4V, Ti 6-4, Ti64, Grade 5 titanium, Titanium Grade 5, UNS R56400, Grade 23 titanium (ELI), Ti-6Al-4V ELI, UNS R56407, Ti 3.7165, TC4, AMS 4911, AMS 4928
Ti-6Al-4V (Grade 5) is the titanium alloy: 895 MPa (130 ksi) tensile at 56% of steel's density, biocompatible, but slow to machine and costly. Values annealed.
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At a glance
| Density | 4.43 g/cm³ (0.16 lb/in³) |
|---|---|
| Tensile strength | 895 MPa (130 ksi) min; typically 950 MPa (138 ksi) |
| Yield strength | 828 MPa (120 ksi) min; typically 880 MPa (128 ksi) |
| Hardness | 36 HRC (about 334 HB) |
| Elongation | 10% min; typically 14% |
| Modulus of elasticity | 114 GPa (16.5 Msi) |
| Thermal | Melts at about 1604-1660 °C (2920-3020 °F); thermal conductivity ~6.7 W/m·K; beta transus about 995 °C (1825 °F); service to about 400 °C (750 °F) |
| Composition | Ti, 5.5-6.75% Al, 3.5-4.5% V, up to 0.40% Fe, up to 0.20% O (Grade 23 ELI: up to 0.13% O, up to 0.25% Fe) |
Typical values, Annealed (mill annealed bar and plate per AMS 4928 / AMS 4911). Solution treated and aged (STA) reaches about 1100 MPa (160 ksi) tensile and 1000 MPa (145 ksi) yield in sections up to about 25 mm (1"). Grade 23 ELI annealed: 860 MPa (125 ksi) tensile, 795 MPa (115 ksi) yield minimum. Confirm against the mill certificate and the purchase spec.
- MachinabilityPoor
- About 20-25% of the free-machining steel benchmark. Heat stays at the cutting edge because the alloy conducts so little, and the chip welds to the tool. Rigid setups, sharp coated carbide, low surface speed, constant chip load and high-pressure flood coolant; never dwell or rub. Expect 4-8x the cycle time of 6061.
- WeldabilityGood
- Welds well by TIG, plasma, laser and electron beam with ERTi-5 filler and complete inert shielding; stress relieve afterward. Fatigue-critical welds are usually EB in vacuum. Weld colour is inspected: silver passes, blue or grey is rejected.
- FormabilityPoor
- Cold forming is limited to gentle radii with large springback; production forming is hot, at 540-815 °C (1000-1500 °F), or superplastic at about 900 °C (1650 °F). Sheet metal parts in Ti-6Al-4V are hot-formed or made from CP titanium instead.
- Corrosion resistanceExcellent
- Immune to seawater, chlorides and oxidizing media like Grade 2, with slightly less margin in reducing acids and hot brines. Biocompatible; the implant alloy. Isolate from aluminum and steel fasteners in wet service, where titanium is the cathode.
Ti-6Al-4V is the alpha-beta titanium alloy that accounts for more than half of all titanium used. Aluminum stabilizes the alpha phase and vanadium the beta phase, giving a heat-treatable alloy with about 895 MPa (130 ksi) minimum tensile strength annealed and up to 1100 MPa (160 ksi) solution treated and aged, at 4.43 g/cm3. That strength-to-weight ratio, with excellent corrosion resistance, fatigue strength and biocompatibility, is why it carries aircraft structure, landing gear, engine fan blades, fasteners, hip and knee implants, racing components and pressure vessels.
Grade 23, or ELI (extra low interstitial), is the same alloy with oxygen held to 0.13% and iron to 0.25%. It gives up a little strength (860 MPa / 125 ksi minimum) for better fracture toughness and ductility, and it is the version specified for implants (ASTM F136) and for cryogenic and damage-tolerant aerospace parts. When a drawing says Ti-6Al-4V without a grade, it means Grade 5.
The alloy is difficult to work, and quotes reflect it. It machines at a fraction of steel speeds because it holds heat at the cutting edge and reacts with tool materials; it forms only hot, with heavy springback; it welds well but only under full inert shielding; and any heating in air above about 600 °C (1100 °F) leaves an alpha case that must be removed. Shops that run titanium every day have the tooling and the coolant to do it well; shops that do not will struggle. It is also the most common metal for 3D printing, where its high raw material cost and poor machinability turn into an advantage.
Heat treatment
Mill anneal at about 700-790 °C (1300-1450 °F) and air cool, the condition most bar and plate is sold in. Solution treat and age (STA) for the highest strength: solution treat at about 900-955 °C (1650-1750 °F), water quench within seconds, then age at about 480-595 °C (900-1100 °F) for 4-8 hours; hardenability limits the full response to sections under about 25 mm (1"). Stress relieve after machining or welding at about 480-650 °C (900-1200 °F) for 1-4 hours. Beta anneal above the transus improves fracture toughness and crack growth resistance at some cost in strength. Heat treat in vacuum or inert atmosphere, or remove the alpha case afterward.
Tempers and conditions
- Annealed (mill annealed, the standard condition)
- Solution treated and aged (STA)
- Beta annealed
- Duplex annealed
- Grade 23 ELI, annealed
Stock forms
- Round bar and billet
- Plate
- Sheet and strip
- Die and hand forgings
- Seamless tube (limited)
- Wire and fastener stock
- Powder for additive manufacturing
Relative cost
Tier 5 of 5. Roughly 8-15x the price of 304 stainless per pound, and machining runs 4-8x the time of aluminum, so a machined Ti-6Al-4V part often costs 5-10x the same part in 6061. Printing and near-net forging exist largely to cut that buy-to-fly ratio.
Typical applications
- Aircraft structural fittings, frames and landing gear components
- Jet engine fan blades, disks and compressor parts
- Aerospace fasteners and rivets
- Orthopedic implants and dental implants (Grade 23 ELI)
- Surgical instruments and medical device components
- Racing and high-performance automotive parts: valves, connecting rods, springs
- Marine and offshore shafts, fasteners and riser components
- Pressure vessels and high-pressure gas bottles
- Bicycle frames and premium sporting goods
Process compatibility
How Ti-6Al-4V takes each process, and what to specify. Each process links to its own guide and to the shops that do it.
| Process | Rating | Notes |
|---|---|---|
| CNC Machining | FairFair | The way most Ti-6Al-4V parts are made, at a price: 4-8x the cycle time of aluminum, in a shop set up for titanium with rigid machines and high-pressure coolant. Is titanium hard to machine? |
| Swiss Machining | FairFair | Standard for bone screws, dental implants and small fasteners from Grade 23 bar; slow but precise. |
| Wire EDM | GoodGood | Cuts titanium cleanly regardless of hardness; remove the recast layer on fatigue-critical surfaces. |
| TIG Welding | GoodGood | ERTi-5 filler, full argon shielding with trailing shield and purge, then stress relieve. Weld colour inspection is the acceptance test. |
| Forging | ExcellentExcellent | The major aerospace forging alloy: closed-die forgings for fittings, landing gear, blades and implants, machined after forging with alpha case removed. |
| Metal 3D Printing | ExcellentExcellent | The most printed metal after stainless: laser and electron beam powder bed, and directed energy deposition, followed by HIP and finish machining for aerospace and implants. |
| Investment Casting | GoodGood | Cast in vacuum foundries for aerospace and golf club heads; hot isostatic pressing closes porosity. Only a few U.S. foundries do it. |
| Heat Treating | GoodGood | STA raises strength to about 1100 MPa (160 ksi) in sections under 25 mm (1"); stress relief after machining and welding. Vacuum furnace or alpha case removal. |
| Waterjet Cutting | ExcellentExcellent | No heat, no alpha case; the standard way to blank plate for machined parts. |
| Laser Cutting | FairFair | Cuts sheet with inert assist gas, but the edge is oxidized and hardened and needs to be removed on any fatigue-critical or formed part. |
| Anodizing | GoodGood | Titanium anodize (AMS 2488): Type II for anti-galling on fasteners and moving parts, Type III for colour identification on implants and instruments. Can titanium be anodized? |
| Shot Peening | ExcellentExcellent | Routine on fatigue-critical forgings, springs and fasteners (AMS 2430); substantial fatigue life gains on this alloy. |
| Press Brake Forming | PoorPoor | Cold bends need very large radii and spring back heavily; production parts are hot formed. Use Grade 2 for cold-formed sheet parts. |
| Die Casting | Not recommendedNot recommended | Titanium cannot be die cast; molten titanium attacks every die material. Investment casting in vacuum is the only casting route. |
Compare Ti-6Al-4V
Design and sourcing tips
- Specify the grade and condition: "Ti-6Al-4V per AMS 4928, annealed" for bar, "AMS 4911" for sheet and plate, "Grade 23 ELI per ASTM F136" for implants.
- Design to the modulus: 114 GPa is 55% of steel, so a titanium part sized by stiffness needs about 20% more section depth than the steel part it replaces.
- Keep machined features simple where you can: deep narrow pockets, small internal radii and thin walls multiply cycle time in titanium far more than in aluminum.
- Call out full inert shielding and weld colour acceptance on welded parts, and stress relief after welding or heavy machining if the part must stay stable.
- Ask for alpha case removal on anything hot formed, forged or heat treated in air; the brittle surface layer starts fatigue cracks.
- Specify shot peening (AMS 2430) on fatigue-critical parts, and anti-galling anodize or a dissimilar mating material on any sliding titanium contact.
Frequently asked questions
- What is the difference between Grade 5 and Grade 23 titanium?
- Both are Ti-6Al-4V. Grade 23 (ELI, extra low interstitial) holds oxygen to 0.13% and iron to 0.25%, which lowers minimum tensile strength from 895 to 860 MPa (130 to 125 ksi) but raises ductility and fracture toughness. Grade 23 is specified for surgical implants (ASTM F136) and for cryogenic and damage-tolerant aerospace parts; Grade 5 is the general structural grade.
- Is Ti-6Al-4V hard to machine?
- Yes. It conducts heat so poorly that the cutting edge runs hot, and titanium reacts with tool materials, so tools wear fast unless speeds are kept low and coolant pressure high. A shop set up for titanium machines it routinely at about 4-8x the cycle time of 6061 aluminum; a shop that is not will burn tools and miss tolerances.
- Can Ti-6Al-4V be welded?
- Yes, well, by TIG, plasma, laser or electron beam with ERTi-5 filler, provided the hot metal is completely shielded from air by argon or vacuum. Welds are followed by a stress relief at about 480-650 °C (900-1200 °F). Weld colour is the acceptance check: silver is good, straw acceptable, blue or grey means contamination and the weld is cut out.
- How strong is Ti-6Al-4V compared to steel?
- Annealed Ti-6Al-4V has about 895 MPa (130 ksi) minimum tensile, similar to 4140 quenched and tempered to around 30 HRC, at 56% of the weight. Solution treated and aged it reaches about 1100 MPa (160 ksi). Its stiffness is only 55% of steel, so it wins on strength per pound but not on stiffness per pound.
- Is Ti-6Al-4V biocompatible?
- Yes. The stable titanium oxide surface does not react with tissue and bone grows onto it (osseointegration), so Ti-6Al-4V ELI (Grade 23, ASTM F136) is the standard alloy for hip and knee stems, bone plates, screws and dental implants. Grade 5 (ASTM F1472) is also used for implants; ELI is preferred where toughness matters.
Processes that commonly use it
Related materials
Where to verify these values
- AMS 4911, AMS 4928 and AMS 4965 (property minimums by form and condition)
- ASTM B265, B348 and ASTM F136 / F1472
- MMPDS (MIL-HDBK-5) design allowables
- ASM Handbook, Volume 2 (Properties and Selection: Nonferrous Alloys)
