TA4 is a representative α-type titanium alloy in China’s titanium alloy classification system, primarily composed of titanium and aluminum. As an α-alloy, it features excellent corrosion resistance, good weldability, and stable performance at moderate temperatures, making it suitable for applications requiring reliability in harsh environments. Below is a detailed overview:
1. Core Identity: TA4 in Chinese Standards
Standard Classification: Defined by China’s national standards GB/T 3620.1 (titanium and titanium alloy designations) and GB/T 13810 (wrought titanium alloys for medical use).
Alloy Type: α-type titanium alloy, consisting mainly of the α-phase (a stable hexagonal close-packed structure at room temperature). α-alloys are non-heat-treatable (strength is primarily adjusted via cold working) and retain good ductility and toughness even at elevated temperatures.
2. Chemical Composition (GB/T 3620.1, mass fraction, %)
TA4’s composition is centered on titanium and aluminum, with strict limits on impurities:
Element Content Range Role in the Alloy
Titanium (Ti) Balance Matrix element, forming the base structure
Aluminum (Al) 2.0–3.0% Strengthens the α-phase, improves high-temperature stability and tensile strength; also refines grain structure
Iron (Fe) ≤0.30% Controlled impurity (excess reduces corrosion resistance and ductility)
Oxygen (O) ≤0.15% Enhances α-phase strength but lowers ductility if excessive
Carbon (C) ≤0.08% Prevents brittle carbide formation
Nitrogen (N) ≤0.05% Avoids embrittlement (high levels cause brittleness)
Hydrogen (H) ≤0.015% Critical for preventing hydrogen embrittlement
3. Key Properties
(1) Mechanical Properties (typical values, annealed condition)
Tensile Strength: 540–690 MPa (lower than α+β alloys like TC4 but sufficient for non-high-strength applications).
Yield Strength: 440–590 MPa (good resistance to permanent deformation under moderate loads).
Elongation: 15–25% (excellent ductility, enabling easy forming via rolling, forging, or bending).
Hardness: ~25–30 HRC (softer than TC4, improving machinability for complex shapes).
Fatigue Strength: ~300–350 MPa (suitable for static or low-cycle dynamic loads).
(2) Physical & Chemical Properties
Density: ~4.51 g/cm³ (lighter than steel, similar to other titanium alloys).
Melting Point: ~1660°C (can operate at temperatures up to 350°C without significant property degradation).
Corrosion Resistance: Excellent—resists corrosion in seawater, industrial chemicals (e.g., dilute acids, alkalis), and atmospheric conditions (forms a dense, self-healing TiO₂ oxide layer).
Thermal Conductivity: ~7.0 W/(m·K) (low, requiring controlled cooling during machining/welding to avoid overheating).
4. Processability & Heat Treatment
Heat Treatment: As an α-alloy, TA4 is not strengthened by heat treatment (no phase transformation to manipulate). Annealing (600–700°C, air cooling) is used to relieve stress and improve ductility after cold working.
Machinability: Moderately machinable with carbide tools and adequate cooling (low thermal conductivity can cause tool overheating).
Weldability: Excellent—welded joints retain most of the base metal’s strength and corrosion resistance (common methods: TIG, plasma arc welding).
Formability: Good ductility allows cold forming (bending, rolling) and hot forming (forging at 800–900°C) into complex shapes.
5. Applications
TA4’s strengths in corrosion resistance, ductility, and weldability make it ideal for:
Chemical & Marine Engineering: Pipes, valves, pumps, and heat exchangers in chemical processing plants (resists corrosive fluids) and marine environments (seawater exposure).
Medical Industry: Non-implant medical devices (e.g., surgical tools, instrument housings) due to corrosion resistance and biocompatibility (though less common than TC4 for implants).
Aerospace: Secondary structural components (e.g., fuel lines, ducting) where moderate strength and weldability are prioritized over ultra-high strength.
General Engineering: Architectural components, food processing equipment, and desalination systems (benefiting from corrosion resistance and lightweight properties).
6. Why Choose TA4?
TA4 stands out for its:
Superior Corrosion Resistance: Outperforms many steels and even some β-titanium alloys in aggressive environments.
Excellent Weldability: Critical for fabricating large or complex structures (e.g., pressure vessels).
Cost-Effectiveness: More affordable than high-strength α+β alloys like TC4, suitable for applications where extreme strength is unnecessary.
In summary, TA4 is a reliable α-type titanium alloy valued for its corrosion resistance, weldability, and formability, serving as a cost-effective solution in chemical, marine, and general engineering fields.
