What Is Grade 5 Titanium Alloy (Ti-6Al-4V)?

What Is Grade 5 Titanium (Ti-6Al-4V)?

Grade 5 titanium, universally known as Ti-6Al-4V, is an alpha-beta titanium alloy containing nominally 6% aluminium and 4% vanadium. It is the most widely used titanium alloy in the world, accounting for the majority of all titanium alloy production, and it is the reference material for aerospace, medical, marine and high-performance industrial applications. Its popularity comes from a combination that few materials match: minimum tensile strength of 895 MPa in the annealed condition, density of only 4.43 g/cm³ (about 60% of steel), excellent corrosion resistance, and service capability up to roughly 400°C. This article explains its composition, properties and applications so that buyers can specify it with confidence.

Chemical Composition

Grade 5 is a medium-strength alpha-beta alloy whose properties are set by tight chemistry control. Per ASTM B348 (bar and billet) the composition is: aluminium 5.50-6.75%, vanadium 3.50-4.50%, iron ≤ 0.40%, oxygen ≤ 0.20%, carbon ≤ 0.08%, nitrogen ≤ 0.05%, hydrogen ≤ 0.015%, with the balance titanium. Aluminium stabilises the alpha phase and strengthens the alloy at room and elevated temperature; vanadium stabilises the beta phase and improves hot workability; oxygen and iron are controlled because they raise strength at the cost of ductility. The same chemistry is covered internationally by ISO 5832-3 for the implant version and by GB/T 3620.1 designations in China.

Mechanical Properties

In the annealed condition, the minimum mechanical properties required by ASTM B348 are 895 MPa ultimate tensile strength, 828 MPa yield strength (0.2% offset) and 10% elongation. Typical annealed product achieves 950-1050 MPa UTS with 12-16% elongation. After solution treatment and ageing (STA), strength rises to roughly 1100 MPa UTS with some loss of ductility. Fatigue strength is excellent, which is why Ti-6Al-4V carries cyclic loads in airframes, rotating machinery and implants. The alloy retains useful strength to about 400°C for continuous service, and its creep resistance is far superior to aluminium alloys, making it the default choice for engine and airframe components that run hot.

Why Grade 5 Is So Widely Used

The value of Ti-6Al-4V lies in the balance, not in any single extreme. It offers the highest practical strength-to-weight ratio among common structural metals; it resists corrosion in seawater, chlorides, oxidising acids and most industrial chemicals through its stable oxide film; it is heat-treatable over a wide strength range; and it can be forged, rolled, machined and welded with established procedures. For an engineer, this means one material covers airframe fittings, pressure vessels, fasteners, shafts, surgical instruments and sports equipment - simplifying certification, supply and maintenance. That versatility is why Grade 5 is called the workhorse of titanium alloys.

Applications by Industry

Aerospace - engine fan and compressor blades and discs, airframe structural members, landing-gear components, fasteners and hydraulic tubing. Every gram saved by the 60% density advantage lowers fuel burn.

Medical - surgical instruments, and in its ELI variant (Grade 23, ASTM F136) load-bearing implants such as hip stems, bone screws and spinal rods.

Automotive and motorsport - connecting rods, valves, exhaust systems, suspension springs and chassis hardware where unsprung weight matters.

Marine - propeller shafts, seawater pump components, deep-sea housings and fasteners exposed to saltwater.

Chemical processing - heat exchangers, pressure vessels, valves and piping for oxidising and chloride media.

High-performance consumer goods - bicycle frames, golf club heads, diving equipment and premium watch cases.

Heat Treatment and Weldability

Grade 5 can be supplied annealed (the standard condition, good formability and toughness), or solution-treated and aged for maximum strength. STA consists of solutionising at 900-955°C, rapid cooling, and ageing at 480-595°C; it is specified when the design is strength-limited. Welding is carried out with GTAW (TIG) or electron-beam welding under strict inert-gas shielding, because molten titanium absorbs oxygen and nitrogen from air, which embrittles the weld. A qualified welding procedure (for example to AWS D17.1 or ISO 15614-5) and careful surface preparation are mandatory. Machining requires low cutting speeds, high feed, rigid setups and abundant coolant, since the alloy work-hardens and conducts heat poorly - a factor buyers should weigh when sourcing machined parts.

Grade 5 vs Commercially Pure Titanium

Commercially pure grades (Grade 1-4) are unalloyed, softer and more formable, with outstanding corrosion resistance but tensile strength of only 240-550 MPa. Grade 5 trades some formability for more than double the strength of Grade 2 at nearly the same density and corrosion resistance. The selection rule is simple: if the design is limited by load, fatigue or temperature, use Grade 5; if it is limited by forming, welding or cost in a benign environment, a CP grade may serve better and cheaper.

FAQ

Why is Grade 5 titanium alloy so widely used?

Because it offers the best practical balance of high strength, low density, corrosion resistance, weldability and established supply chain data, making it the default choice across aerospace, medical, marine and industrial applications.

What is the chemical composition of Ti-6Al-4V?

Titanium balance, aluminium 5.5-6.75%, vanadium 3.5-4.5%, iron ≤ 0.40%, oxygen ≤ 0.20%, carbon ≤ 0.08%, nitrogen ≤ 0.05% and hydrogen ≤ 0.015% per ASTM B348.

What are the key mechanical properties of annealed Grade 5?

Minimum 895 MPa tensile strength, 828 MPa yield strength and 10% elongation per ASTM B348. Solution treatment and ageing raise strength to about 1100 MPa at some cost in ductility.

Can Grade 5 titanium be heat treated?

Yes. Alpha-beta alloys respond to solution treatment and ageing (STA), which precipitates fine secondary phases and increases strength compared with the annealed condition. CP titanium grades cannot be strengthened this way.

Is Grade 5 titanium corrosion resistant?

Yes. Its stable oxide film gives excellent resistance in seawater, chloride solutions and oxidising chemicals. It is not recommended for reducing acids such as concentrated hydrochloric acid, where palladium-bearing grades are used.

Can Grade 5 be welded?

Yes, with GTAW (TIG) or electron-beam welding under strict inert-gas shielding and a qualified procedure per AWS D17.1 or ISO 15614-5. Without shielding, atmospheric pickup embrittles the weld.

What is the difference between Grade 5 and Grade 23 titanium?

Grade 23 (Ti-6Al-4V ELI) is the extra-low-interstitial version with oxygen capped at 0.13%, giving higher fracture toughness and ductility for implant applications per ASTM F136 and ISO 5832-3. Grade 5 is the general engineering grade per ASTM B348.