TC6 (Ti-4Al-3Mo-1V) is a heat-treatable alpha-beta titanium alloy in the Chinese GB/T system. If your part needs titanium’s density and corrosion behaviour plus a strength level between annealed Ti-6Al-4V and the higher-alloyed TC11, and you can work within the heat-treatment and machining constraints below, TC6 is a reasonable candidate. If you need the widest mill-product availability and the most published machining data, TC4 (Ti-6Al-4V) is usually the safer starting point. Near-equivalent grades are not automatically interchangeable: TC6 is not TC4, not TC11, and not commercially pure TA1/TA2, and a drawing that says “Ti-4Al-3Mo-1V” without a condition is not a complete specification.
What TC6 actually is
TC6 is an alpha-beta titanium alloy. Aluminium is an alpha-phase stabiliser; molybdenum and vanadium are beta-phase stabilisers. That combination is what makes the alloy heat treatable by solution treatment plus ageing, unlike single-phase commercially pure titanium, which is not strengthened by that route.
The grade lives in the Chinese GB/T system. GB/T 3620.1 covers titanium and titanium alloy designations and chemical composition; GB/T 2965 covers titanium alloy bars; GB/T 3620.2 covers permissible composition tolerances for product analysis. When you write the grade on a drawing or RFQ, write it as the designation plus the standard plus the condition, for example “TC6, bar per GB/T 2965, annealed” or “TC6, solution treated and aged”. Writing only “Ti-4Al-3Mo-1V” leaves the supplier guessing about product form, condition and tolerances.
Titanium alloys as a family sit around 4.4–4.5 g/cm³. That is a family figure for titanium alloys, not a TC6-specific measured value, and it is roughly 55–60% of steel density — useful for mass-sensitive parts, but it also means the same volume of metal removes faster in terms of mass and generates heat into a smaller thermal mass.
Supply and heat-treatment conditions
Two conditions matter most to a buyer:
Annealed. The mill supplies bar in a stress-relieved or annealed condition. This is the most stable, most machinable and most predictable state. It is the right choice when you need moderate strength, good ductility and dimensional stability, or when the part will be formed or welded before final machining.
Solution treated and aged (STA). The part is solution treated at elevated temperature, cooled, then aged to precipitate strengthening phases. This raises strength and hardness at some cost in ductility and toughness. It also introduces distortion risk: the heat treatment happens after or between machining operations, so you must plan stock allowance and finishing passes around it. Not every product form and section size responds identically, so the achievable property level depends on product form, section and the specific heat-treat cycle — not on the grade name alone.
Do not assume a supplier’s “TC6” bar is in the condition you need. Specify it.
Mechanical properties: keep them tied to condition
Tensile properties for TC6 depend on product form (bar, forging, wire), section size and heat-treatment condition. The table below keeps each value tied to its condition and test method. Where a value is not reliably attributable to a specific condition, it is omitted rather than guessed.
| Property | Condition | Test method / source | Note |
|---|---|---|---|
| Tensile strength, yield strength, elongation | Annealed bar | Tensile testing per GB/T 228.1 or ASTM E8/E8M | Values vary with product form and section; take them from the mill certificate for the actual bar |
| Tensile strength, yield strength, elongation | Solution treated and aged | Tensile testing per GB/T 228.1 or ASTM E8/E8M | Higher strength, lower ductility than annealed; exact level depends on heat-treat cycle and section |
| Hardness | As supplied / after ageing | ASTM E384 (microindentation) or equivalent | Hardness is a poor proxy for tensile properties in titanium; use it for consistency checks, not design allowables |
For design allowables, use the values on the mill certificate for the specific product form and condition you are buying, or the values in the applicable GB/T or ASTM product specification. Do not merge numbers from one specification into another and treat the result as authoritative.
Corrosion and temperature behaviour
Titanium’s corrosion resistance comes from a thin passive TiO₂ oxide film that forms spontaneously and re-forms when damaged. This is not a stainless-steel chromium oxide film, and the comparison should not be carried across. Titanium generally performs well in chloride-bearing and oxidising media; it is not universally resistant, and reducing acids or fluoride-bearing environments can attack it. If your service environment is aggressive, test the actual alloy in the actual medium rather than assuming from the family.
At elevated temperature, two titanium-specific risks matter:
Alpha-case. Oxygen diffuses into the surface at high temperature and forms a hard, oxygen-enriched layer. Alpha-case is brittle and can crack under load; it must be removed by machining, not left on a finished surface. This is titanium behaviour, not a steel heat-treatment effect.
Hydrogen pickup. Titanium can absorb hydrogen at elevated temperature, leading to embrittlement. Avoid hydrogen-bearing atmospheres and pay attention to pickling and cleaning processes.
Why titanium machines differently
Titanium has low thermal conductivity, so heat generated at the cutting edge does not leave the cut quickly. It concentrates in the tool and the workpiece surface. Titanium is also chemically reactive at cutting temperature, which promotes chip welding and built-up edge. The alloy work hardens, so a rubbing cut is worse than a clean one. It has a relatively low modulus, so slender parts deflect and spring back more than steel under the same cutting force.
Finally, titanium fines are a fire and oxygen hazard. Fine chips and dust can ignite, and a titanium fire is difficult to extinguish. Keep chips clear, avoid dry machining where possible, use appropriate coolants, and follow your shop’s titanium housekeeping rules.
Tooling and process approach
Treat every cutting value as a conditional starting point. Machine rigidity, tool grade and geometry, coating, coolant type and pressure, workpiece rigidity, and the material condition all change the result. A value that works on an annealed bar on a rigid machine may fail on a thin STA section.
Practical starting points: use sharp, positive-geometry carbide tools; keep the tool engaged to avoid rubbing; maintain a steady feed rather than dwelling; use generous coolant flow to move heat away; and expect to adjust after the first article. Do not accept a promised fixed Ra or tolerance from a supplier who has not seen the drawing and the material condition. Surface finish and tolerance are outcomes of the whole setup, not properties of the grade.
For a broader view of what to prepare before quoting, see the CNC machining quote checklist. If you are planning a first article, the first article inspection checklist covers what to verify. And if volume and tooling cost are open questions, the notes on low-volume CNC machining cost, MOQ and lead time are worth reading before you commit.
Where TC6 fits
Alpha-beta titanium like TC6 suits parts that need titanium’s density and corrosion behaviour plus a strength level above annealed commercially pure titanium, in sections that can be machined and, where required, heat treated. Typical fits include structural brackets and fittings, shafts and fasteners, and components in chloride-bearing or mildly oxidising service. Whether a specific part is acceptable for a regulated application depends on the applicable standard, qualification and certification requirements — not on the alloy’s properties alone. Do not derive aerospace, medical-implant or food-compliance suitability from a material property.
Comparison with the nearest alternatives
Compare grades in the same condition and on comparable metrics:
| Grade | Family | Nominal composition | Key difference |
|---|---|---|---|
| TC6 | Alpha-beta, heat treatable | Ti-4Al-3Mo-1V | Lower Al, Mo+V beta stabilisers; heat treatable |
| TC4 / Ti-6Al-4V | Alpha-beta, heat treatable | Ti-6Al-4V | Higher Al, V beta stabiliser; the most widely available and best-documented titanium alloy |
| TC11 | Alpha-beta, heat treatable | Ti-Al-Mo-Zr-Si system | Adds Zr and Si; different property balance, not a drop-in for TC6 |
TC4 and TC6 are both alpha-beta titanium, but they are different alloys with different compositions and different property balances. TC11 adds zirconium and silicon, which changes its behaviour again. A “near-equivalent” grade is not automatically interchangeable: substituting one for another changes strength, ductility, heat-treatment response, machinability and corrosion behaviour. If a substitution is proposed, it needs engineering review and, where applicable, customer approval.
Drawing and RFQ checklist
Before you request a quote, prepare:
- Designation and standard: TC6 per GB/T 3620.1, with bar per GB/T 2965 and composition tolerances per GB/T 3620.2 where relevant.
- Material condition: annealed or solution treated and aged, stated explicitly.
- Product form and size: bar diameter or forging envelope, and whether you will supply material.
- Quantity: prototype, pilot and production volumes separately.
- Tolerances: critical dimensions, datums and any GD&T callouts.
- Surface finish: required Ra on functional surfaces, and which surfaces are cosmetic only.
- Heat treatment: whether it is in scope, and whether it happens before or after machining.
- Inspection: what you need measured, and whether a first article report is required.
- Service environment: temperature, medium and any chloride or oxidising exposure.
Send your drawing, material specification and grade, material condition, quantity, tolerances and surface-finish requirements to request a quote.
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