Ti-6Al-4V Titanium Alloy
Ti-6Al-4V (also known as TC4 in Chinese standards) is the most widely used titanium alloy globally, valued for its exceptional balance of strength, toughness, corrosion resistance, and lightweight properties. As an α+β dual-phase alloy, it combines the advantages of α-phase stability and β-phase ductility, making it versatile across industries from aerospace to medical devices. Below is a comprehensive overview:
1. Basic Classification & Structure
Alloy Type: α+β titanium alloy (dual-phase structure, with α and β phases coexisting; phase ratio adjustable via heat treatment).
Key Traits:
High strength-to-weight ratio (stronger than many steels but ~40% lighter).
Excellent corrosion resistance (resists seawater, acids, and industrial chemicals).
Good fatigue strength and toughness at room temperature.
Processable via forging, machining, welding, and 3D printing.
2. Chemical Composition (mass fraction, %)
Its composition is optimized for balanced performance:
Element Content Range Role in the Alloy
Titanium (Ti) Balance Matrix element, providing base properties
Aluminum (Al) 5.5 – 6.75% Strengthens the α phase, improves strength and heat resistance
Vanadium (V) 3.5 – 4.5% Stabilizes the β phase, enhances ductility, toughness, and heat treatability
Iron (Fe) ≤0.30% Controlled impurity (excess reduces corrosion resistance)
Oxygen (O) ≤0.20% Strengthens α phase but limits ductility if over 0.2%
Carbon (C) ≤0.08% Impurity control (avoids brittle carbide formation)
Nitrogen (N) ≤0.05% Impurity control (excess causes embrittlement)
3. Key Properties
(1) Mechanical Properties (typical values, annealed condition)
Tensile Strength: 900 – 1100 MPa (room temperature).
Yield Strength: 800 – 950 MPa (room temperature).
Elongation: 10 – 15% (good ductility for forming).
Impact Toughness: ≥40 J/cm² (excellent resistance to sudden loads).
Hardness (HRC): 30 – 36.
Density: ~4.43 g/cm³ (about 1/2 the density of steel, 2/3 that of aluminum alloys).
(2) Thermal & Corrosion Resistance
Service Temperature: Short-term use up to 400°C; long-term stable service at ≤300°C (lower than high-temperature alloys like TC11 but sufficient for most structural applications).
Corrosion Resistance: Exceptional in seawater, industrial chemicals (e.g., acids, alkalis), and atmospheric environments (passive oxide layer protects against degradation).
(3) Processability
Machining: Machinable but requires sharp tools and low cutting speeds (titanium’s low thermal conductivity can cause tool overheating).
Welding: Excellent weldability (compatible with TIG, laser, and electron beam welding); welded joints retain ~85 – 95% of base metal strength.
Forming: Good hot formability (e.g., forging, rolling) at 800 – 900°C; cold forming is possible for simple shapes but may require annealing.
Heat Treatment: Adjustable properties via solution treatment (920 – 950°C) + aging (450 – 550°C) to enhance strength (up to 1100 MPa) or annealing (700 – 800°C) for improved ductility.
4. Applications
Ti-6Al-4V’s versatility makes it indispensable in diverse fields:
Aerospace & Aviation:
Airframe components (wings, fuselages, landing gear).
Engine parts (fan blades, casings) operating at moderate temperatures.
Rocket and spacecraft structures (lightweight and corrosion-resistant).
Medical Devices:
Orthopedic implants (joint replacements, bone plates) – biocompatible, non-toxic, and similar in stiffness to human bone.
Dental implants and surgical instruments.
Marine Engineering:
Ship propellers, offshore oil rig components, and seawater pipes (resists saltwater corrosion).
Automotive & Sports:
High-performance vehicle parts (valves, exhaust systems) and sports equipment (golf clubs, bicycle frames) for weight reduction.
5. Comparison with Other Alloys
Property Ti-6Al-4V TC11 (High-Temp) Pure Titanium (CP Ti)
Tensile Strength 900-1100 MPa 950-1100 MPa 240-550 MPa
Density 4.43 g/cm³ 4.5 g/cm³ 4.51 g/cm³
Service Temp ≤300°C 500°C ≤200°C
Corrosion Resistance Excellent Excellent Superior
Cost Moderate High Low (pure Ti)
Summary
Ti-6Al-4V is the “workhorse” of titanium alloys, prized for its unmatched balance of strength, toughness, corrosion resistance, and lightweight properties. Its adaptability to machining, welding, and heat treatment, combined with broad serviceability across temperatures and environments, makes it the material of choice in aerospace, medicine, marine, and many other industries. Its ubiquity stems from the rare ability to meet diverse performance demands while remaining cost-effective relative to specialized titanium alloys.