Ti-6Al-2Sn-4Zr-6Mo (Grade 7)
Introduction to Ti-6Al-2Sn-4Zr-6Mo (Grade 7)
Ti-6Al-2Sn-4Zr-6Mo, commonly known as Grade 7 titanium, is a high-strength alpha-beta alloy specifically designed for high-temperature service. With excellent creep resistance, good weldability, and strong corrosion resistance, this alloy is widely used in aerospace turbine components and advanced propulsion systems.
Its structural stability and performance in oxidizing environments make Ti-6Al-2Sn-4Zr-6Mo ideal for precision CNC-machined titanium parts. Manufacturers rely on high-accuracy CNC machining services to meet tight tolerances for mission-critical parts subjected to cyclic stress and extreme heat.
Chemical, Physical, and Mechanical Properties of Ti-6Al-2Sn-4Zr-6Mo (Grade 7)
Chemical Composition (Typical)
Element | Composition Range (wt.%) | Key Role |
|---|---|---|
Titanium (Ti) | Balance | Provides structural integrity and corrosion resistance |
Aluminum (Al) | 5.5–6.5 | Alpha stabilizer, improves high-temperature strength |
Tin (Sn) | 1.8–2.5 | Enhances creep resistance and thermal stability |
Zirconium (Zr) | 3.6–4.5 | Increases oxidation resistance |
Molybdenum (Mo) | 5.5–6.5 | Beta stabilizer that enhances hardenability and fatigue strength |
Silicon (Si) | ≤0.25 | Improves creep properties |
Oxygen (O) | ≤0.15 | Strengthening interstitial |
Iron (Fe) | ≤0.30 | Residual element |
Hydrogen (H) | ≤0.015 | Controlled to prevent hydrogen embrittlement |
Physical Properties
Property | Value (Typical) | Test Standard/Condition |
|---|---|---|
Density | 4.65 g/cm³ | ASTM B311 |
Melting Range | 1600–1670°C | ASTM E1268 |
Thermal Conductivity | 6.4 W/m·K at 100°C | ASTM E1225 |
Electrical Resistivity | 1.68 µΩ·m at 20°C | ASTM B193 |
Thermal Expansion | 8.5 µm/m·°C | ASTM E228 |
Specific Heat Capacity | 570 J/kg·K at 20°C | ASTM E1269 |
Elastic Modulus | 112 GPa | ASTM E111 |
Mechanical Properties (Annealed Condition)
Property | Value (Typical) | Test Standard |
|---|---|---|
Tensile Strength | 895–1000 MPa | ASTM E8/E8M |
Yield Strength (0.2%) | 825–900 MPa | ASTM E8/E8M |
Elongation | ≥10% | ASTM E8/E8M |
Hardness | 320–360 HB | ASTM E10 |
Creep Resistance | Excellent | ASTM E139 |
Fatigue Resistance | High | ASTM E466 |
Key Characteristics of Ti-6Al-2Sn-4Zr-6Mo (Grade 7)
Exceptional Creep Strength: Withstands prolonged exposure at temperatures up to 500°C, making it ideal for turbine engines and thermal shielding structures.
High-Temperature Fatigue Resistance: Engineered to perform under cyclic thermal and mechanical loads, Grade 7 excels in jet engine and afterburner environments.
Corrosion and Oxidation Resistance: The Sn and Zr additions promote the formation of a dense oxide layer, providing strong resistance to scaling in oxidizing atmospheres.
Good Weldability: Ti-6Al-2Sn-4Zr-6Mo can be reliably welded with post-weld heat treatment to retain strength and structure despite its high alloy content.
CNC Machining Challenges and Solutions for Grade 7 Titanium
Machining Challenges
High Strength and Low Conductivity: Strengths approaching 1000 MPa and thermal conductivity of 6.4 W/m·K require careful thermal management during cutting.
Aggressive Work Hardening: This alloy rapidly works hardens if the chip load is inadequate, which can lead to tool damage and dimensional inaccuracies.
Tool Adhesion and Edge Wear: The alloy sticks to cutting tools and causes abrasive wear, especially on uncoated inserts.
Springback and Elastic Recovery: The high modulus (112 GPa) results in elastic deflection, challenging form control in finishing passes.
Optimized Machining Strategies
Tool Selection
Parameter | Recommendation | Rationale |
|---|---|---|
Tool Material | Submicron carbide or CBN inserts | Ideal for tough alloys and high heat resistance |
Coating | AlTiN or TiSiN (3–5 µm PVD) | Improves thermal protection and minimizes galling |
Geometry | Positive rake, honed cutting edge | Reduces cutting force and chip adhesion |
Cutting Speed | 20–50 m/min | Reduces heat and tool wear |
Feed Rate | 0.08–0.20 mm/rev | Maintains chip thickness |
Coolant | High-pressure emulsion ≥100 bar | Enhances cooling and chip evacuation |
Ti-6Al-2Sn-4Zr-6Mo (Grade 7) 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 7 Titanium Parts
Hot Isostatic Pressing (HIP) eliminates internal voids and enhances mechanical strength and fatigue life in structural turbine components.
Heat Treatment improves creep resistance and phase stability by aging at 550–650°C for 2–8 hours.
Superalloy Welding allows secure joints in pressure systems and aerospace assemblies using compatible Ti-6-2-4-6 fillers.
Thermal Barrier Coating (TBC) protects Grade 7 parts from thermal oxidation and flame exposure in engines and reactors.
CNC Machining enables high-tolerance fabrication of turbine rings, ducts, and hot-section components with accuracy down to ±0.01 mm.
Electrical Discharge Machining (EDM) ensures precision in intricate features and thin-walled parts without inducing heat-affected zones.
Deep Hole Drilling achieves high L/D ratios for coolant channels, with bore straightness <0.3 mm/m and Ra ≤ 1.6 µm.
Material Testing includes SEM, creep testing, ultrasonic NDT, and phase stability evaluations to meet aerospace and energy industry specs.
Material Testing and Analysis
Validation includes mechanical testing at elevated temperatures, creep rupture analysis, XRD for phase evaluation, and full ultrasonic or eddy current inspection to aerospace standards.
Industry Applications of Ti-6Al-2Sn-4Zr-6Mo (Grade 7)
Aerospace: Used in turbine rings, afterburner liners, and jet engine casings exposed to thermal extremes.
Power Generation: Ideal for high-temperature piping, blades, and fuel system hardware.
Defense: Components such as exhaust hoods, missile parts, and structural fasteners for heat resistance and strength.
Industrial Equipment: Applied in corrosive, cyclic thermal environments like furnaces, heat exchangers, and pressure vessels.
FAQs
What are the best machining practices for Ti-6Al-2Sn-4Zr-6Mo (Grade 7)?
How does Grade 7 titanium compare to Grade 5 in high-temperature fatigue applications?
What post-processing is recommended for improving Grade 7 fatigue resistance?
Which engine or turbine components are commonly produced using this alloy?
What tolerances and surface finishes are achievable when CNC machining Grade 7?
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