TA7 is the Chinese designation for a near-alpha titanium alloy, corresponding to Ti-5Al-2.5Sn under international standards such as ASTM Grade 6. It contains aluminum (5.0–6.0 percent) as an alpha stabilizer and tin (2.0–3.0 percent) as a neutral strengthener. The alloy does not contain beta-stabilizing elements, resulting in a predominantly alpha-phase microstructure. This gives TA7 excellent weldability, good high-temperature strength, and outstanding resistance to oxidation and creep, but limited room-temperature ductility and poor cold formability.

The nominal chemical composition of TA7 is: aluminum 5.0 to 6.0 percent, tin 2.0 to 3.0 percent, iron up to 0.30 percent, oxygen up to 0.15 percent, carbon up to 0.08 percent, nitrogen up to 0.05 percent, hydrogen up to 0.015 percent, and the balance titanium.

Key mechanical properties (typical for annealed condition):

● Tensile strength: 735 to 860 MPa (minimum 735 MPa)

● Yield strength (0.2% offset): 685 to 790 MPa

● Elongation: 12 to 15 percent

● Reduction of area: 25 to 30 percent

● Density: 4.42 g/cm³

● Melting point: approximately 1,580°C

● Modulus of elasticity: 110 GPa

TA7 offers good creep resistance up to approximately 500°C (930°F) and retains useful strength up to 550°C for short durations. It exhibits excellent thermal stability and oxidation resistance in air at elevated temperatures. The alloy is readily weldable by gas tungsten arc welding (GTAW), electron beam welding, and resistance welding, with minimal loss of ductility in the weld zone. Unlike alpha-beta alloys (e.g., TC4), TA7 is not heat treatable to high strength levels; it is used exclusively in the annealed condition. Cold working is difficult due to limited ductility, but hot working (above 800°C) is performed easily.

Typical applications of TA7 include:

● Aerospace: welded components in jet engines and airframes, such as engine casings, ducting, firewalls, and structural supports operating at moderate temperatures (300–500°C).

● Cryogenic applications: TA7 retains good ductility at very low temperatures (down to -196°C), making it suitable for liquid hydrogen and liquid oxygen storage tanks.

● Chemical processing: equipment requiring high-temperature corrosion resistance and weldability, such as heat exchangers and reactor linings.

● Military: welded missile and rocket components.

Comparison with TC4 (Ti-6Al-4V): TA7 has lower room-temperature strength but superior weldability, better creep resistance at moderate temperatures, and better low-temperature ductility. TC4 is stronger and more versatile for general structural use, while TA7 is preferred for welded assemblies and cryogenic applications.

Selection guidance: Choose TA7 when excellent weldability, moderate-temperature strength (up to 500°C), and cryogenic toughness are required, and when heat treatment is not needed. For higher strength at room temperature or broader availability, TC4 is the more common choice. For simple corrosion-resistant applications, commercially pure titanium (TA1–TA4) may suffice.