If your drawing specifies TC4 (Ti-6Al-4V / Ti6Al4V, registered internationally as UNS R56400 / ASTM Grade 5), this is a near-α+β titanium alloy offering the best all-round balance of strength, toughness, weldability and corrosion resistance among general-purpose titanium grades — but it machines well only with disciplined tooling, low surface speeds and rigid setups. For a turned or milled component carrying real load, corrosion exposure or weight constraints, TC4 is usually the right answer; where raw-material cost and machining difficulty outweigh the performance benefit, a commercially pure grade such as TA2 (Grade 2) may serve better. This guide confirms the material’s identity and standard designations, gives representative annealed composition and mechanical values tied to the GB/T, ASTM and ISO specification systems, and covers the machining and inspection points that decide whether your Ti-6Al-4V part quotes and produces successfully.
Identity, standard designation and how to write the grade
TC4 is the Chinese national designation for the alloy corresponding to internationally traded 6Al-4V titanium. The designation is not arbitrary: in the GB/T 3620.1 designation system, “TC” marks a titanium alloy in which the balanced aluminium-equivalent and molybdenum-equivalent place it in the alpha + beta (α+β) field at room temperature, and “4” refers to a nominal 4% vanadium. It is the single most widely used titanium alloy, which strongly affects availability and cost (see our post on why TC4 dominates the titanium market), and its two main elements, aluminium (~6 wt.%) and vanadium (~4 wt.%), are the origin of the informal name “6-4 titanium.”
When you write it on a drawing or RFQ, be explicit about which system you mean, because the same book-keeping letters appear in different standards:
- GB/T 2965 (China) — wrought TC4 bars for structural use; check GB/T 3620.1 for the designation and GB/T 3620.2 for permitted composition deviations on delivered product.
- ASTM B265 (USA) — sheet, strip and plate; defines Grade 5 as Ti-6Al-4V.
- UNS R56400 — the unified alloy code used on North American drawings instead of “Grade 5.”
- ASTM F136 (and ISO 5832-3) — the extra-low interstitial (ELI) variant used for surgical implant applications, with tighter oxygen/iron control and generally lower strength for the same hardenability. Do not assume standard TC4 is automatically implant-compliant; that is a separate material and requirement.
The “TC4” of the GB system and “Grade 5” of the ASTM system are near-equivalent, not formally interchangeable specifications. If either your drawing or your supplier uses a different designation from the other, confirm the governing document (and any customer spec that overrides it) before machining — interstitial element limits, permitted tolerances and test frequency differ.
Supply / heat-treatment states you will actually machine
Most TC4 bar, plate and billet leaving the mill is annealed — recrystallization- or mill-annealed (bars typically ~700–800 °C, air cool) — the state recognised by GB/T 2965 and ASTM B265 for structural supply and the state normally machined. For maximum strength, plate is sometimes supplied solution-treated and aged (STA): solution-treated around 925–955 °C, water quenched, aged around 480–595 °C. STA raises strength but lowers ductility and makes machining harder, especially on interrupted cuts. State annealed vs. STA on your RFQ — they differ in price and machinability, and confusing them is an expensive source of scrap.
Representative chemical composition
Published nominal / allowable ranges for annealed Ti-6Al-4V (all values wt.%, balance titanium unless noted) are:
| Element | Nominal / allowable (wt.%) | Notes |
|---|---|---|
| Aluminium (Al) | 5.5 – 6.75 | Primary alpha stabiliser; raises strength and creep resistance. |
| Vanadium (V) | 3.5 – 4.5 | Beta stabiliser; retains ductility and workability. |
| Iron (Fe) | ≤ 0.40 (max) | Interstitial/impurity control; lower for ELI. |
| Oxygen (O) | ≤ 0.20 (max) | Increases strength but lowers ductility and toughness — the reason ELI restricts it. |
| Carbon (C) | ≤ 0.08 (max) | Controlled impurity. |
| Nitrogen (N) | ≤ 0.05 (max) | Controlled interstitial. |
| Hydrogen (H) | ≤ 0.015 (max) | Kept low to avoid hydrogen embrittlement in welds. |
| Titanium (Ti) | Balance | — |
These ranges are consistent with GB/T 3620.2 and ASTM B265 Grade 5 composition allowances. Always confirm the exact limits against the current standard revision cited on your drawing; small composition differences between the aerospace AMS 4911, implant-grade F136 and general structural B265 variants exist.
Representative ambient mechanical properties (annealed)
The values below are typical for annealed wrought TC4 evaluated at room temperature in the mill-annealed condition, and are intended for early design estimates only — actual minimums are set by the governing specification for your product form:
| Property | Typical annealed value | Material state / test basis |
|---|---|---|
| Ultimate tensile strength (Rm) | ≈ 895 – 1000 MPa | Annealed bar & plate, room temperature; ASTM E8 / GB/T 228.1 tensile test. |
| 0.2% proof / yield strength (Rp0.2) | ≈ 825 – 915 MPa | Same batch, same condition as above. |
| Elongation at break (A) | ≈ 10 – 14% | Annealed, longitudinal testpiece. |
| Reduction of area (Z) | ≈ 20 – 30% | Annealed bar. |
| Modulus of elasticity (E) | ≈ 105 – 120 GPa | About half that of steel — relevant to deflection and to spring-back in machining. |
| Density | ≈ 4.43 g/cm³ | Solid annealed plate. |
| Hardness | ≈ 30 – 38 HRC (typical 32–36) | Annealed; reflectively softer than worn tooling limit but work-hardens during cutting. |
| Thermal conductivity | ≈ 6.7 – 7.5 W/(m·K) at room temp | Roughly 1/6 of steel — the root of most titanium machining problems. |
Use these only as a starting estimate. The controlling minimums (and any STA-condition uplift in strength with the associated ductility loss) must come from the specification cited on your drawing — never assume the annealing-street value is guaranteed if your supplier delivers a harder condition.
Corrosion, temperature and wear behaviour
TC4 forms a dense, self-repairing titanium oxide film giving outstanding resistance to seawater, chlorides and most industrial chemicals at ambient temperature, which is why it is standard for marine fasteners and chemical-process wetted parts. It is not recommended for strongly reducing acids, hot concentrated hydrochloric acid, or hydrofluoric/acetic acid pickling solutions, where the film breaks down and attack is rapid — confirm compatibility against media tests for your exact chemistry.
Mechanically, TC4 retains useful strength to roughly 400–500 °C in short-term service and is a common airframe alloy up to about 300–350 °C; above ~500 °C creep and oxidation become design drivers. Its affinity for oxygen means finely divided titanium swarf can burn near a hot cutting edge — which drives the flood-coolant and chip-waste rules below. Wear resistance of TC4 is modest without treatment; a part bearing against a hard surface should specify nitriding, anodic oxidation or a hard coating rather than rely on the bare alloy.
Why TC4 is genuinely difficult to machine — and the reality of the parameters
The machining difficulty of 6-4 titanium comes from three linked facts: its low thermal conductivity (~6.7–7.5 W/m·K, roughly a sixth of steel) traps cutting heat at the edge; its low elastic modulus (~110 GPa) lets thin parts deflect and spring back, causing chatter and dimensional drift; and it work-hardens quickly, so a tool that rubs rather than cuts blunts fast and can smear the surface. Practically: keep the edge engaged at adequate chip load, use generous flood (preferably through-tool) coolant, and run speeds far lower than for steel of similar hardness. Workpiece rigidity — short overhang, supported thin sections, balanced holding — often decides between holding tolerance and scrapping the part.
The table below gives conservative starting windows for the three common operations on annealed TC4 with coated carbide tooling. They are starting points, not guarantees: your actual values depend on machine rigidity, spindle power, tool holder, coating, coolant type and workpiece geometry, and you should ramp in and tune every one of them on a test piece. Do not treat any of these numbers as a promise of a fixed surface finish or tolerance — the same insert can hold one result on a stiff lathe with a through-coolant boring bar and a different result on a light-duty mill in a thin plate.
| Operation | Cutting speed (m/min) — start | Feed (mm/rev or mm/tooth) | Depth of cut (mm) | Tooling |
|---|---|---|---|---|
| Turning (rough) | 30 – 50 | 0.10 – 0.25 mm/rev | 1.0 – 2.5 | Coated carbide, positive rake insert, sharp edge. |
| Turning (finish) | 40 – 60 | 0.05 – 0.12 mm/rev | 0.2 – 0.5 | Coated or uncoated sharp carbide. |
| Milling | 30 – 60 | 0.05 – 0.12 mm/tooth | 0.5 – 2.0 axial | Solid carbide, high-helix, coated; use trochoidal / high-feed strategies where possible. |
| Drilling | 15 – 25 (peripheral) | 0.05 – 0.12 mm/rev | — | Short, rigid carbide drill with pecking and through-tool coolant; never let it dwell. |
Tooling guidance: indexable or solid carbide with an aluminium/titanium-nitride (AlTiN/TiAlN) or titanium-nitride coating performs well; the coating is not the main event — edge sharpness and free chip flow are. Use high-pressure flood coolant, ideally through-the-tool, and evacuate titanium swarf promptly because fine chips can ignite in the presence of a hot edge. Avoid allowing the tool to dwell or rub in the cut.
Surface finishing and post-processing
As-machined TC4 can deliver a range of surface finishes depending on operation, feed, tool nose radius and rigidity, so if your drawing specifies one, put it on the RFQ with the measurement method. Where an engineered surface is needed, common options include glass-bead/garnet blasting, chemical or electrochemical pickling to remove a damaged alpha case, and — for decorative or anti-galling service — anodising or plasma nitriding/hard coating. Any alpha case from prior hot processing or uncontrolled grinding should be removed before service: it is hard, brittle and cracks easily.
Applications and where a substitute may be justified
Typical CNC-machined components include aerospace structural brackets and fittings, lightweight high-strength fasteners, bicycle and motorsport frames, marine hardware, chemical-process fittings, and welded fabrications, where the alpha-beta structure yields weldable strength. Because the material carries real cost and machining time, compare it honestly against alternatives in the same product form and condition:
- Commercially pure TA1/TA2 (Grade 1/2): much easier to machine and form, excellent corrosion resistance (see our TA10 titanium guide for the related corrosion-service grade),, but roughly half the strength (Rp0.2 ≈ 275–345 MPa for Grade 2 annealed). Choose when corrosion resistance matters more than load capacity.
- Ti-6Al-4V ELI (Grade 23 / TC4 ELI): nearly identical chemistry but lower interstitial (oxygen/iron) content; slightly lower strength, better low-temperature toughness. The implant-grade route — do not substitute standard TC4 if an F136 / ISO 5832-3 callout is the requirement.
- Higher-strength TC11 / Ti-6Al-4Zr-… family: only relevant when you specifically need >1000 MPa plus creep resistance; heavier to source and machine.
For another corrosion-focused metal that is frequently compared for chloride service, see our analysis of S44400 (EN 1.4521) versus 316. No titanium grade is automatically “medical-implant compliant” or “aerospace approved” by being titanium: those are separate material, process and certification requirements. State only what a drawing actually calls out.
What to put on your drawing / RFQ for TC4
To quote and machine TC4 reliably, specify on the drawing/RFQ the exact designation and governing standard (TC4 per GB/T 2965, or Grade 5 per ASTM B265, or UNS R56400 with your customer spec); the required condition (annealed vs. STA); full dimensions and tolerances with their inspection method; surface finish and its measurement standard; whether a material certification is required; and quantity, so a raw-material and test-piece plan can be quoted. A standard annealed structural piece and an implant-grade ELI plate with certification are different products at different prices.
Ready to move forward? Send your drawing, the material specification (standard + grade + condition), quantity, tolerances and surface-finish targets, plus any inspection or certification requirements, and request a quote for TC4 / Ti-6Al-4V components. The clearer the grade, delivery state, quantities and finish on the drawing, the faster a shop can confirm the correct titanium feedstock and machine it to the condition your part actually needs.
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