Titanium Ti-6Al-4V
Designation and classification
Section titled “Designation and classification”The titanium alloy Ti-6Al-4V, commercially known as ASTM Grade 5 or UNS R56400, represents more than 50% of the titanium used in industry due to its optimal balance of strength, weight, and corrosion resistance.
| Designation | Standard | Common names |
|---|---|---|
| Ti-6Al-4V | ASTM B348, B381 | Grade 5, TC4, Ti64 |
| UNS R56400 | AMS 4928, AMS 4965 | Alpha-beta titanium alloy |
Chemical composition
Section titled “Chemical composition”The nominal composition contains 6% aluminum (alpha stabilizer) and 4% vanadium (beta stabilizer), with titanium as balance and controlled impurities to ensure ductility.
| Element | Al | V | Fe (max.) | O (max.) | C (max.) | N (max.) | H (max.) | Ti |
|---|---|---|---|---|---|---|---|---|
| % by weight (min.–max.) | 5.5–6.75 | 3.5–4.5 | 0.30 | 0.20 | 0.08 | 0.05 | 0.015 | Balance |
Mechanical properties by treatment condition
Section titled “Mechanical properties by treatment condition”In the mill annealed condition, tensile strength starts from 900 MPa and rises up to 1200 MPa after solution treatment and aging (STA), with a notable increase in yield strength above 1000 MPa.
| Property | Annealed (typical) | Solution treated and aged (STA) |
|---|---|---|
| Tensile strength (MPa) | 900 – 1 000 | 1 100 – 1 200 |
| Yield strength (0.2%) (MPa) | 828 – 950 | 970 – 1 100 |
| Elongation in 50 mm (%) | 10 – 18 | 5 – 10 |
| Elastic modulus (GPa) | 110 – 114 | 110 – 114 |
| Rockwell C hardness (HRC) | 32 – 36 | 38 – 44 |
Physical properties
Section titled “Physical properties”The density is only 4.43 g/cm³, about 45% lower than stainless steel, providing excellent specific strength.
| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Density | 4.43 – 4.51 g/cm³ | 276 – 282 lb/ft³ |
| Bulk modulus (K) | 96.8 – 153 GPa | 14.0 – 22.2 × 10⁶ psi |
| Poisson’s ratio | 0.31 – 0.37 | 0.31 – 0.37 |
| Fracture toughness (Kᵢc) | 84 – 107 MPa·m¹/² | 76 – 97 ksi·in¹/² |
Thermal properties
Section titled “Thermal properties”Thermal conductivity at room temperature is only 7.1 W/m·K, about ten times lower than aluminum, requiring intensive cooling during machining.
| Property | Value (SI) | Value (Imperial) |
|---|---|---|
| Melting point | 1 878 – 1 933 K (1 605 – 1 660 °C) | 2 921 – 3 020 °F |
| Specific heat (Cp) | 553 – 570 J/kg·K | 0.43 – 0.44 BTU/lb·°F |
| Thermal conductivity (k) | 7.1 – 7.3 W/m·K | 4.1 – 4.2 BTU·ft/h·ft²·°F |
| Coefficient of thermal expansion (α) | 8.7 – 9.1 × 10⁻⁶ /K | 15.7 – 16.4 × 10⁻⁶ /°F |
| Maximum service temperature* | 620 – 690 K (347 – 417 °C) | 656 – 782 °F |
*To maintain mechanical strength in structural applications.
Corrosion resistance
Section titled “Corrosion resistance”In exposure to seawater and marine environments, Ti-6Al-4V obtains a maximum rating of 5/5, equivalent to virtually total immunity to corrosion.
| Medium | Resistance (1=poor, 5=excellent) |
|---|---|
| Fresh water | 5 |
| Seawater | 5 |
| Weak acids / Weak alkalis | 5 |
| Organic solvents | 5 |
| Oxidation at 500 °C | 4 |
| Strong acids | 4 |
| Wear | 3 |
Weldability, machinability, and heat treatments
Section titled “Weldability, machinability, and heat treatments”Low thermal conductivity and high strength limit cutting speeds to 30–60 m/min with carbide tools, although the alloy is weldable by gas tungsten arc welding (TIG/GTAW) if the weld zone is protected from atmospheric contamination.
| Treatment | Temperature | Cooling | Purpose |
|---|---|---|---|
| Mill anneal | 700 – 785 °C (1–2 h) | Air | Equiaxed α-β microstructure |
| Duplex anneal | 900 – 950 °C (1 h) + 540 °C (8 h) | Air | Improved ductility and toughness |
| Solution treatment | 940 – 970 °C (1 h) | Water/oil quench | Maximum aging response |
| Aging (STA) | 480 – 600 °C (4–8 h) | Air | High mechanical strength |
Applications by industry
Section titled “Applications by industry”More than 15% of the structural weight of the Boeing 787 is titanium, mostly Ti-6Al-4V, present in critical components such as landing gear, wing-to-fuselage joints, and compressor blades.
| Industry | Typical applications |
|---|---|
| Aerospace | Aircraft airframe structures, engine blades and discs, fasteners |
| Medical | Joint prostheses (hip, knee), dental implants, bone screws |
| Automotive | Racing engine components, valves, connecting rods |
| Marine | Propeller shafts, valves, seawater heat exchangers |
| Chemical processing | Reactors, tanks, and piping for nitric acid or chlorides |
Comparison with similar materials
Section titled “Comparison with similar materials”Compared to high-strength aluminum 7075-T6, Ti-6Al-4V provides about 20% higher specific strength and much higher corrosion resistance, although its cost is 5 to 10 times higher.
| Material | Density (g/cm³) | Tensile strength (MPa) | Specific strength (kN·m/kg) | Marine corrosion resistance |
|---|---|---|---|---|
| Ti-6Al-4V (annealed) | 4.43 | 950 | 214 | Excellent (5/5) |
| Titanium Grade 2 (CP) | 4.51 | 345 | 76 | Excellent (5/5) |
| Al 7075-T6 alloy | 2.81 | 572 | 204 | Poor (requires protection) |
| Stainless steel 304 | 8.00 | 580 | 73 | Good (3/5) |
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the density of Ti-6Al-4V?
Section titled “What is the density of Ti-6Al-4V?”The typical density is 4.43 g/cm³, representing a weight saving of 45% compared to common stainless steel.
What tensile strength can be achieved?
Section titled “What tensile strength can be achieved?”In the annealed condition, values between 900 and 1000 MPa are obtained, while after solution treatment and aging the strength exceeds 1100 MPa.
At what temperature does this alloy melt?
Section titled “At what temperature does this alloy melt?”The melting range lies between 1605 °C and 1660 °C (1878–1933 K), typical of titanium alloys.
What is the modulus of elasticity?
Section titled “What is the modulus of elasticity?”The Young’s modulus ranges between 110 and 119 GPa, approximately half that of steel, providing greater flexibility.
What is the thermal conductivity?
Section titled “What is the thermal conductivity?”The thermal conductivity at room temperature is 7.1–7.3 W/m·K, being about 1/10 that of pure aluminum.
What corrosion resistance does it exhibit in seawater?
Section titled “What corrosion resistance does it exhibit in seawater?”In marine environments the rating is 5 out of 5, indicating total immunity to pitting and crevice corrosion.
References
Section titled “References”- azom.com: https://www.azom.com/properties.aspx?ArticleID=1547
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/properties-aluminum-pipe-d_1340.html