Why Ti-6Al-4V shows up on drawings
Ti-6Al-4V, often called Grade 5 titanium, is the workhorse titanium alloy for machined parts. It offers a high strength-to-weight ratio, good corrosion resistance in many environments and useful performance at elevated temperature compared with aluminum. It is also slower and more demanding to machine than common aluminum or steel alloys, and raw stock costs more. This guide explains when those trade-offs pay off and how to design parts so they machine reliably.
What the alloy is
Ti-6Al-4V is an alpha-beta titanium alloy with about 6% aluminum and 4% vanadium. The most common condition for machined parts is annealed. Solution-treated and aged conditions raise strength further for demanding applications. Commercially pure (CP) titanium grades are softer, more formable and often chosen for corrosion-focused or formed parts rather than high-strength machined structures.
Typical handbook figures for annealed Ti-6Al-4V (confirm against your certificate) sit in this range:
| Property | Typical annealed Ti-6Al-4V |
|---|---|
| Density | About 4.43 g/cm³ |
| Typical yield strength | Roughly 800–900 MPa class |
| Typical tensile strength | Roughly 900–1000 MPa class |
| Elastic modulus | About 110–115 GPa |
| Melting range | High compared with aluminum |
Density is roughly 60% of steel and about 1.6× aluminum. Strength is far above common aluminum alloys and competitive with many steels at much lower weight. Stiffness (modulus) is about half that of steel, so titanium parts can deflect more than a steel part of the same geometry under the same load even when they are stronger.
Where titanium earns its place
Strength-to-weight
When mass is limited and loads are high—flight hardware, racing components, portable equipment, robotics arms—titanium often beats aluminum that would need thicker sections and steel that would be too heavy.
Corrosion resistance
Titanium forms a stable oxide film and resists many corrosive media that attack steels. Marine, chemical and medical environments frequently specify titanium for this reason. Surface finish and cleanliness still matter; titanium is not immune to every chemical attack, and galvanic couples with other metals need design attention.
Temperature
Ti-6Al-4V retains useful strength at temperatures where many aluminum alloys soften. For short-term or moderate elevated-temperature service it is a common choice. For very high continuous temperatures, specialist alloys or other material families may be required.
Biocompatibility context
Certain titanium alloys are widely used in medical devices where biocompatibility and corrosion resistance matter. Regulatory and clean-processing requirements sit outside general machining advice; treat medical work as its own specification stack.
Machining challenges you should plan for
Titanium is machinable, but it is not "like aluminum, only stronger."
- Low thermal conductivity: heat stays in the cutting zone and in the tool rather than leaving with the chip
- Chemical affinity for tool materials at high temperature: tools can wear rapidly if speeds are too aggressive
- Relatively low modulus: thin walls flex under cutting forces, which can cause chatter and dimensional error
- Work hardening tendency: rubbing or dull tools make the next pass harder
Practical responses from the shop side include sharp tooling, controlled speeds and feeds, rigid setups, generous coolant where appropriate and avoiding dwelling in the cut. From the design side, the responses are thicker walls where possible, reachable features, realistic tolerances and avoiding unnecessary deep narrow pockets.
Design rules that keep titanium parts manufacturable
Wall thickness and bosses
Treat thin walls more carefully than you would in aluminum. Flexure and chatter are more likely. If a wall must be thin for weight, allow the shop to use finishing strategies and avoid stacking tight tolerances on both faces of a skinny wall.
Internal corners and pockets
Internal vertical corners need a radius at least as large as the cutter radius—the same rule as any CNC pocket—but deep titanium pockets amplify tool-pressure and heat issues. Prefer fewer, more open pockets over labyrinthine cavities when function allows.
Holes and threads
Standard drills and taps work, but deep small holes and fine threads in titanium deserve extra review. Thread milling is often preferred for critical or expensive parts. Helical inserts in titanium are used when repeated assembly would wear native threads.
Fixturing access
Leave clean clamping surfaces. Oddball shapes that cannot be held rigidly force soft jaws, glue-ups or custom fixtures that add cost—more painful on expensive stock.
Stock and grain
Bar, plate and billet availability vary by size. Very large thin plates or odd diameters may have long lead times. Design around stock forms that are commonly stocked when schedule matters.
Comparing titanium to aluminum and stainless (decision view)
| Need | Often better in | Notes |
|---|---|---|
| Lowest mass at high strength | Ti-6Al-4V | Aluminum needs more section; steel is heavier |
| Lowest material and machine cost | Aluminum (e.g. 6061) | Default for many brackets and housings |
| General corrosion, lower cost | Stainless 304/316 | Heavier; different machining behaviour |
| Welded frames | Often 6061 or stainless | Ti welding is specialised |
| Cosmetic anodize color matching | Aluminum | Titanium finishes differently |
| Seawater / aggressive media | Ti or suitable stainless | Confirm chemistry and temperature |
If aluminum meets strength with acceptable mass, it is usually the economical default. Move to titanium when weight, corrosion or temperature calculations show aluminum or steel will not work.
Finishing and joining notes
Titanium can be bead blasted, polished or left as-machined. Anodizing of titanium exists for colour and some surface effects but is not the same process family as aluminum Type II/III anodizing. Passivation concepts familiar from stainless do not transfer one-for-one; follow the finish specification written for titanium.
Welding titanium requires inert gas shielding and clean practice; contamination embrittles welds. Many machined Ti-6Al-4V parts are designed to avoid welding and use fasteners or integral features instead. Brazing and adhesive bonding appear in specialised assemblies—treat them as process-specific decisions.
Tolerances and inspection
Do not tighten every dimension "because titanium is expensive." Expensive stock makes scrap painful, which is an argument for manufacturable tolerances, not for blanket precision. Put tight tolerances only on functional fits and datums. Leave generous tolerances on non-critical stock faces and cosmetic edges.
First-article inspection and material certificates are common on titanium jobs because alloy identity and condition matter. Call out the specification (for example ASTM or AMS designations used on your drawing) and the required condition clearly.
Cost drivers (qualitative)
Without quoting prices, expect:
- Higher raw material cost per kilogram than aluminum or many steels
- Longer cycle times and more cautious tooling strategies
- Greater sensitivity to scrap, rework and fixture mistakes
- Possible longer stock lead time for uncommon sizes
Design moves that save money usually reduce machine time and scrap risk: open features, realistic walls, clear datums and avoiding ornamental complexity.
Common mistakes
- Specifying Ti-6Al-4V for a part that only needed aluminum weight savings of a few percent
- Copying an aluminum pocket design with knife-edge walls into titanium
- Calling out welded titanium structures without a welding process plan
- Omitting the alloy condition (annealed vs heat-treated)
- Demanding mirror cosmetics on deep pockets that will chatter
- Treating titanium like stainless for finishing callouts
Writing a clear material callout
Name the alloy and condition, for example "Ti-6Al-4V annealed" or the exact specification and condition your industry uses. State any prohibited substitutions. If CP titanium is acceptable for a less loaded part, say so—Grade 2 machines more gently and may fit corrosion-only needs.
Next steps
If weight, corrosion or temperature is pushing you toward titanium, upload the model and describe the loads and environment. The reviewing engineer can confirm whether Ti-6Al-4V is justified, suggest geometry tweaks that protect thin walls and recommend whether a blank-plus-machine or solid-from-billet approach fits the part.