Titanium Grade 5 (Ti-6Al-4V) CNC Machining

Nearly three times the strength, at the same weight

Grade 5 and Grade 2 share titanium’s density and its corrosion behaviour. They part company on strength.

	Grade 2	Grade 5
Alloying	None — commercially pure	~6% aluminium, ~4% vanadium
Tensile, annealed	~345 MPa	~950 MPa
Density	~4.51 g/cm³	~4.43 g/cm³
Thermal conductivity	Very low	Lower still
Machinability	Difficult	More difficult
Chosen for	Corrosion resistance	Strength-to-weight

At roughly 950 MPa annealed and a density of 4.43 g/cm³, Grade 5 delivers a specific strength no steel reaches. A hardened 4140 at 1,000 MPa with a density of 7.85 g/cm³ carries about 127 kN·m/kg; Grade 5 carries around 214. Aluminium alloys such as 7075 reach similar specific strength figures — but they lose it quickly as temperature rises, and titanium does not.

That is the whole case for the alloy, and it explains the applications: structures where every kilogram matters and the part still has to carry load. Aerospace airframes and engine components, high-strength fasteners, medical implants, motorsport suspension and driveline parts, and downhole oil and gas equipment.

Where the reason for using titanium is corrosion rather than strength, Grade 2 is the cheaper and easier answer. Where the reason is weight and the part carries load, Grade 5 is the grade.

Heat treatment

Unlike Grade 2, Grade 5 responds to heat treatment. It is an alpha-beta alloy — it contains both phases — and a solution treat followed by an age raises the strength above the annealed figure.

In practice, most machined Grade 5 parts are used in the mill-annealed condition, because that already delivers roughly 950 MPa and heat treating adds two problems to the route: distortion, and a finishing operation afterwards to bring dimensions back. Where a drawing carries a specific heat-treated condition, that is worth flagging at the enquiry, because it changes the process plan rather than merely the material certificate.

One service limit is worth stating alongside the heat treatment: Grade 5 is usable to roughly 400 °C. Above that, sustained exposure causes oxidation and oxygen uptake at the surface, which embrittles the metal. Where a part runs continuously hot, the service temperature belongs on the enquiry — it affects the grade choice, and in some cases it points away from titanium entirely.

Machining Grade 5: the same problems, less margin

The four difficulties that make titanium awkward all apply, and Grade 5 gives you less room on each.

Heat. Grade 5’s thermal conductivity is lower than commercially pure titanium’s, which is already a fraction of steel’s. Cutting heat has nowhere to go except into the tool edge. This is the dominant constraint on the whole operation.

Galling. Titanium welds to the cutting edge when it is hot, producing built-up edge and a smeared rather than sheared surface. Grade 5’s higher strength makes the cut more demanding and the effect more pronounced.

Deflection. The modulus is roughly half steel’s, so thin walls and slender sections push away from the tool. On a high-strength material, chatter is not only a finish problem — it is a tool-life and dimensional problem at the same time.

Combustible swarf. Fine titanium chips burn. A titanium fire is class D — extremely hot, and water makes it worse rather than better. This is managed as a process hazard, not treated as a curiosity.

What works

• Sharp, high-positive-geometry tooling, replaced early. On titanium, a dull edge does not merely cut worse; it begins the heat-and-gall cycle that ruins both the part and the tool. Tool life is short by the standards of any other material and it is planned for.
• Low cutting speeds. Titanium is cut slowly. Increasing speed converts directly into edge temperature, and edge temperature is what ends the tool.
• Generous feed per tooth and decisive depths of cut. A light rubbing pass generates heat without removing material — the worst possible combination on this material, and Grade 5 work-hardens more readily than Grade 2.
• Copious coolant at high pressure, directed at the edge. This is the primary heat-removal mechanism because the material will not conduct heat away. Never machine titanium dry.
• Maximum rigidity. Short tool overhangs, solid fixturing, and support under thin sections. Where a part is thin-walled or slender, saying so at the enquiry lets the setup be planned rather than improvised on the machine.
• Continuous chip clearance. Fines are cleared as they are made, and the machine is cleaned of titanium swarf before the next job.

Surface finish is a specification, not a detail

Grade 5 is notch sensitive. A machining mark, a scratch, an un-radiused corner or a sharp edge change concentrates stress, and under cyclic loading that concentration becomes the origin of a fatigue crack.

This has a practical consequence that is easy to miss when the drawing is written: on a fatigue-loaded Grade 5 part, the surface finish and the edge condition are functional requirements. A part produced to the correct dimensions with a torn surface and sharp corners may pass dimensional inspection and still fail in service.

So where a part is cyclically loaded, say so at the enquiry. That lets three things be planned:

• The finishing route, which may include controlled polishing or a surface treatment
• The edge treatment, so that sharp transitions are radiused rather than left as machined
• The inspection, so that the surface is checked as a feature rather than assumed

The same principle applies to the anisotropy of the material. Grade 5’s properties differ along and across the working direction, and where a part carries a primary load, the direction of the grain relative to that load matters. On a critical part that is worth stating.

Precision features are held to ±0.01 mm with ISO 2768-m as the general tolerance block — see tolerances we hold. Titanium will hold the tolerance; what it costs to get there is where the difference lies.

Corrosion behaviour

Grade 5’s corrosion performance is broadly similar to Grade 2’s, and the same rules apply.

Excellent in: sea water and brine, chlorides, oxidising acids such as nitric, wet chlorine and hypochlorite.

Attacked by: reducing acids such as hydrochloric and dilute sulphuric, hydrofluoric acid at any concentration, and dry chlorine gas.

One nuance at high strength: at the strength levels Grade 5 reaches, stress-corrosion cracking becomes a consideration in some environments in a way it is not for the lower-strength Grade 2. A part carrying high sustained tensile stress in an aggressive environment deserves the specific chemistry and temperature stated, rather than an assumption that “titanium does not corrode”.

Where Grade 5 is the right choice

• Aerospace structural components and airframe fasteners, where weight and strength both matter
• Medical implants — hip stems, bone plates, spinal hardware, dental components — where strength, inertness and biocompatibility are all required
• Surgical instruments that need stiffness and corrosion resistance in repeated sterilisation
• High-performance and motorsport components — suspension, driveline, fasteners
• Oil and gas downhole equipment, where high strength meets aggressive chemistry
• Marine hardware carrying real load — not fittings, but structural parts
• High-strength fasteners where a steel fastener would be too heavy or would corrode
• Any part where the weight saving is worth the machining cost and the part carries load

Where Grade 5 is the wrong choice

The reason for using titanium is corrosion only. Grade 2 resists the same environments at lower cost and machines more easily. Paying for 950 MPa you do not use is the most common way to overspend on a titanium part.

The duty is within what stainless handles. In flowing sea water at moderate temperature, 316L performs adequately and machines far more easily. Titanium earns its cost where the chloride duty is beyond 316L, or where the weight saving matters.

A reducing acid or hydrofluoric acid is involved. Titanium is attacked quickly. The chemical and the temperature should be stated before a grade is quoted.

Sustained service above roughly 400 °C. Oxygen uptake embrittles the surface. A different material family is the answer.

Very high strength in a benign environment. Where weight is not critical and the environment is mild, a hardened 4140 or 17-4PH reaches comparable strength at a fraction of the material and machining cost.

A part that will be machined to a sharp-edged, rough surface finish under fatigue load. Grade 5 is notch sensitive, and the finish is a functional requirement rather than a cosmetic one.

Finishing Grade 5

• Anodizing — grows the oxide film to a controlled thickness. Titanium oxide produces colour by light interference rather than pigment, so different thicknesses give different colours with no dye. The film is thicker and harder than the natural oxide.
• Passivation — removes iron contamination picked up from steel tooling and fixtures, which would otherwise rust on the surface of an inert part.
• Sand blasting — a uniform matte surface, often as preparation before anodizing or as a finish in its own right.
• Polishing and brushing — used on medical and visible parts, and where a fatigue-loaded surface has to be controlled.
• Peening — a controlled surface treatment used to introduce compressive stress at the surface of fatigue-critical parts.
• Pickling — removes heat tint and alpha case from welded or heat-treated components.

The contamination point is worth repeating, because it is the most common cosmetic complaint on titanium: titanium picks up iron from steel tooling, fixtures and brushes, and that iron then rusts on the surface of a corrosion-resistant part. It looks like the titanium has failed when it has not. Keeping steel away from finished parts, and passivating after any operation where contact occurred, is the standard control.

All finishing runs through our vetted partner network, managed under one quality process. The grades we run across every process are listed on the materials page.

What to put on the drawing

Instead of	Write
Titanium	Titanium Grade 5 (Ti-6Al-4V), where the part carries load
Titanium, corrosion is the only driver	Grade 2 costs less and machines more easily
Grade 5, annealed or heat treated	State the condition — it changes the process route, not just the certificate
Grade 5, fatigue loaded	Say so — surface finish and edge radius are functional requirements
Grade 5, primary load direction	Say so — the material is anisotropic
Grade 5, runs above ~400 °C	Wrong material — oxygen uptake embrittles the surface
Grade 5, reducing acid or HF	Wrong material — titanium is attacked
Grade 5, thin wall or slender	Say so — low modulus means the setup is planned around deflection
Grade 5, needs sharp as-machined edges	Radius them — notch sensitivity makes sharp edges a fatigue risk

The three lines that decide most Grade 5 specifications are whether the part carries load, whether it is fatigue critical, and how hot it runs. The first decides whether Grade 5 is needed or Grade 2 will do. The second decides the finishing route and the edge treatment. The third decides whether titanium belongs in the application at all.

Material is bought against your drawing for your job, and every batch ships with a material certificate (MTR) tracing the grade and condition to its mill heat plus pre-shipment photos of the actual parts. Orders start at 50 pieces per style and material, samples from a single piece in 5–10 days, and production runs in 25–35 days after sample approval. Send the drawing through the request a quote form and the reply comes back within 24 hours with DFM feedback — including a note on the geometry, the coolant strategy and the fatigue-critical surfaces where any of them need settling.