Ti-5Al-2. 5Sn (Grade 6)
Introduction to Ti-5Al-2.5Sn (Grade 6)
Ti-5Al-2.5Sn, designated as Grade 6 titanium, is a near-alpha titanium alloy offering a combination of moderate strength, excellent weldability, and superior creep resistance. It is particularly engineered for elevated temperature service in aerospace, marine, and power generation environments.
Thanks to its thermal stability and consistent performance in oxidizing atmospheres, Ti-5Al-2.5Sn is a reliable choice for critical CNC-machined titanium parts. High-performance CNC machining services are used to deliver precision components with exceptional dimensional accuracy, even for complex, thin-walled aerospace structures.
Chemical, Physical, and Mechanical Properties of Ti-5Al-2.5Sn (Grade 6)
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Titanium (Ti) | Balance | Provides corrosion resistance and structural stability |
Aluminum (Al) | 4.5–5.5 | Alpha stabilizer, improves strength and oxidation resistance |
Tin (Sn) | 2.0–3.0 | Improves creep and thermal fatigue resistance |
Oxygen (O) | ≤0.15 | Strengthens matrix but affects ductility |
Iron (Fe) | ≤0.30 | Residual element |
Hydrogen (H) | ≤0.015 | Needs control to prevent hydrogen embrittlement |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 4.54 g/cm³ | ASTM B311 |
Melting Range | 1600–1650°C | ASTM E1268 |
Thermal Conductivity | 7.1 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.60 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 8.3 µm/m·°C | ASTM E228 |
Specific Heat Capacity | 565 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 110 GPa | ASTM E111 |
Mechanical Properties (Annealed Condition)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 745–860 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 690–790 MPa | ASTM E8/E8M |
Elongation | ≥10% | ASTM E8/E8M |
Hardness | 280–320 HB | ASTM E10 |
Creep Resistance | Excellent | ASTM E139 |
Fatigue Resistance | High | ASTM E466 |
Key Characteristics of Ti-5Al-2.5Sn (Grade 6)
Excellent High-Temperature Performance: Maintains mechanical strength and creep resistance up to 450°C, ideal for jet engine ducts and afterburner structures.
Superior Weldability: Grade 6 offers excellent weld integrity without significant degradation in mechanical properties—ideal for pressure vessels and aerospace tubing.
Thermal Stability: Exhibits low thermal expansion (8.3 µm/m·°C) and high resistance to thermal fatigue, supporting performance in high-cycle heat load environments.
Oxidation Resistance: Stable TiO₂ surface layer formation protects parts from scaling and corrosion in hot gas and marine atmospheres.
CNC Machining Challenges and Solutions for Grade 6 Titanium
Machining Challenges
Toughness and Low Conductivity: High toughness combined with thermal conductivity of just 7.1 W/m·K leads to excessive heat generation at the cutting zone, causing tool wear.
Work Hardening Behavior: Ti-5Al-2.5Sn hardens during machining if chip load is insufficient, affecting the quality of tool life and surface finish.
Tool Adhesion Risk: Formation of built-up edge (BUE) occurs at high temperatures, impacting accuracy and increasing the chance of galling.
Dimensional Accuracy: Elastic recovery and springback (modulus ~110 GPa) demand compensation for maintaining dimensional control on precision features.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Carbide or CBN inserts | Suitable for high-temperature wear resistance |
Coating | AlTiN or TiAlSiN (3–5 µm PVD) | Minimizes adhesion and heat-related degradation |
Geometry | Sharp rake, honed edges | Reduces force and enhances chip evacuation |
Cutting Speed | 20–60 m/min | Balances thermal load and surface finish |
Feed Rate | 0.10–0.25 mm/rev | Ensures proper chip formation |
Coolant | High-pressure emulsion ≥100 bar | Prevents heat accumulation and reduces friction |
Ti-5Al-2.5Sn (Grade 6) Cutting Parameters (ISO 3685 Compliance)
Operation | Speed (m/min) | Feed (mm/rev) | Depth of Cut (mm) | Coolant Pressure (bar) |
|---|---|---|---|---|
Roughing | 20–30 | 0.15–0.20 | 2.0–3.0 | 80–100 (Through-tool) |
Finishing | 45–65 | 0.05–0.10 | 0.2–0.5 | 100–150 |
Surface Treatment for Grade 6 Titanium Parts
Hot Isostatic Pressing (HIP) increases part density and eliminates internal voids, enhancing fatigue performance in turbine and propulsion parts.
Heat Treatment involves stress relieving and aging at ~600°C, optimizing creep resistance and dimensional stability.
Superalloy Welding enables full-strength welds with minimal porosity and cracking in pressure-rated aerospace systems.
Thermal Barrier Coating (TBC) protects Grade 6 parts from oxidation and thermal fatigue in jet engine exhaust or chemical reactors.
CNC Machining enables ±0.01 mm precision and is critical for manufacturing engine ducts, control housings, and precision aerospace tubing.
Electrical Discharge Machining (EDM) allows the creation of precision holes and cooling channels without introducing thermal stress.
Deep Hole Drilling achieves high L/D ratios with straightness <0.3 mm/m and Ra ≤ 1.6 µm, suitable for pressure tubing and ductwork.
Material Testing includes creep rupture validation, SEM microstructure review, and ultrasonic flaw detection for quality assurance.
Material Testing and Analysis
Grade 6 parts undergo high-temperature tensile testing, creep evaluation, fatigue life testing, and XRD/SEM analysis to ensure integrity in aerospace, nuclear, and marine service conditions.
Industry Applications of Ti-5Al-2.5Sn (Grade 6)
Aerospace: Used for jet engine ducts, hydraulic tubing, and airframe skins operating under high thermal load.
Power Generation: High-temperature piping and flow-control components for steam and gas turbines.
Marine: Desalination plant heat exchangers and tubing exposed to hot brine and seawater environments.
Defense: Structures and housings for propulsion and exhaust systems requiring strength-to-weight balance.
Industrial Equipment: Equipment in corrosive and thermal cycling environments, such as reactors and heat exchangers.
FAQs
What are the optimal cutting speeds and feeds for machining Ti-5Al-2.5Sn?
How does Grade 6 titanium perform under thermal cycling in engine environments?
What post-processing treatments improve fatigue life for CNC Grade 6 parts?
Which aerospace components commonly use Ti-5Al-2.5Sn alloy?
How does Grade 6 titanium compare to Grade 4 or Grade 5 in elevated-temperature service?
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