Which Is Stronger:Grade 2 or Grade 5 Titanium

1. Core Differences in Alloy Type & Composition

The root cause of the strength disparity lies in whether the material is "pure titanium" or an "alloyed titanium":

Property	Titanium Grade 2	Titanium Grade 5 (Ti-6Al-4V)
Alloy Category	Commercially Pure Titanium (CP Ti)	α+β Titanium Alloy
Chemical Composition	Titanium (Ti, balance) + trace impurities (max 0.25% O, 0.30% Fe, 0.08% C, etc.)	Titanium (Ti, balance) + 5.5–6.75% Al + 3.5–4.5% V + controlled impurities
Key Design Goal	Ductility, corrosion resistance, and ease of fabrication	High strength-to-weight ratio, fatigue resistance, and creep resistance

Grade 2 relies on pure titanium's inherent properties (with minor impurity strengthening), while Grade 5 is intentionally alloyed with aluminum (Al) and vanadium (V)-elements that drastically boost strength.

2. Direct Strength Comparison (Mechanical Properties)

Industry standards (e.g., ASTM B265 for titanium sheet/plate) define clear differences in tensile strength, yield strength, and hardness-three critical metrics of "strength":

Strength Metric	Titanium Grade 2 (Annealed State)	Titanium Grade 5 (Annealed State)	Titanium Grade 5 (Solution-Treated & Aged, STA)
Tensile Strength	370–480 MPa	860–1100 MPa	1170–1400 MPa
Yield Strength (0.2% Offset)	275–345 MPa	790–1000 MPa	1030–1380 MPa
Brinell Hardness (HBW)	110–150 HBW	280–340 HBW	350–400 HBW

Even in its "softer" annealed state, Grade 5 has more than twice the tensile and yield strength of Grade 2. When heat-treated to the high-strength STA state, Grade 5's strength triples or more compared to Grade 2.

3. Why Grade 5 Is Far Stronger

Grade 5's superior strength comes from two key alloying effects and its microstructural design:

(1) Solid-Solution Strengthening by Al and V

Aluminum (Al): Acts as an α-stabilizer (promotes the strong α-phase) and dissolves into titanium's crystal lattice. Since Al atoms are smaller than Ti atoms, they create localized lattice distortions that block the movement of dislocations (the main mechanism of metal deformation). This directly hardens the material and raises its yield strength.

Vanadium (V): Serves as a β-stabilizer (retains the ductile β-phase at room temperature) and also acts as a solid-solution strengthener. V atoms are larger than Ti atoms, creating additional lattice distortions in the β-phase that further resist dislocation movement.

(2) Age Hardening (for STA State)

Unlike pure Grade 2 (which cannot be strengthened by heat treatment), Grade 5 responds to solution treatment and aging (STA)-a process that unlocks its maximum strength:

Solution treatment: Heat Grade 5 to ~925–950°C (in the α+β phase region) and quench rapidly. This traps excess Al and V atoms in a supersaturated β-phase.

Aging: Reheat to ~500–600°C. Fine, uniformly distributed α-phase particles precipitate from the β-phase. These tiny particles act as "barriers" to dislocations, drastically increasing tensile and yield strength (as seen in the STA state metrics above).

(3) α+β Dual-Phase Microstructure

Grade 5's room-temperature microstructure is a mix of α and β phases. The boundaries between these two phases act as additional obstacles to dislocation movement, enhancing strength beyond what pure titanium (Grade 2, which has a single α-phase microstructure) can achieve.

4. Trade-Offs: Strength vs. Other Properties

While Grade 5 is far stronger, Grade 2 retains advantages in other areas-explaining why both grades are widely used:

Grade 2: Better ductility (elongation: 20–25%, vs. 10–15% for annealed Grade 5), lower cost, easier to weld/form, and slightly better corrosion resistance in some mild environments (e.g., pure water, mild acids). It is ideal for non-load-bearing applications like chemical tanks, heat exchanger tubes, or architectural panels.

Grade 5: Superior strength-to-weight ratio and fatigue resistance, but higher cost and lower ductility. It is reserved for high-load, high-performance applications like aerospace components (aircraft engine parts, landing gear), high-pressure industrial valves, or racing car suspension parts.

Titanium Grade 5 (Ti-6Al-4V) is unambiguously stronger than Titanium Grade 2-with twice the tensile strength in its annealed state and up to three times the strength when heat-treated to the STA state. This strength advantage comes from its alloying with Al and V, its ability to undergo age hardening, and its dual-phase α+β microstructure. Grade 2, by contrast, prioritizes ductility and ease of use over raw strength.