Guide
What are the properties of titanium 6Al-4V, and when is Grade 2 the better choice?
Titanium 6Al-4V is an alpha-beta titanium alloy with nominally 6 percent aluminum and 4 percent vanadium, listed as Grade 5 (UNS R56400) in ASTM B348, and it has roughly three times the yield strength of commercially pure Grade 2 at about the same density. Choose 6Al-4V when strength or fatigue sets the size of the part; choose Grade 2 when formability, weldability or corrosion resistance matters more than strength.
By Saola Manufacturing engineering team · Published · Updated
This guide is for engineers and buyers comparing the two titanium grades that show up most on machined-part drawings. Property values are design allowables from the open military handbook MIL-HDBK-5J (2003), grade definitions are from the scope of ASTM B348/B348M, and stress corrosion ratings are from NASA MSFC-STD-3029A. Thread seizure is a separate problem with its own fixes, covered in the galling guide.
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What strength and stiffness does Ti-6Al-4V have?
Per MIL-HDBK-5J, annealed Ti-6Al-4V bar to AMS 4928 under 0.500 in has a design tensile strength of 135 ksi, a yield of 125 ksi and 10 percent elongation, with a modulus of 16.9 × 10³ ksi.
The stiffness figure is the one that surprises people coming from steel. Titanium is stronger than most aluminum alloys and many steels, but its modulus sits between the two, so a titanium part sized only for strength can deflect more than the steel part it replaced. Check deflection with the handbook modulus, not just stress with the handbook strength.
Section size matters too. Per MIL-HDBK-5J, the full strength potential of Ti-6Al-4V is not available in sections thicker than 1 inch, and the bar allowables step down as the diameter grows, so read the column that matches the stock you will cut from, not the finished part.
| Property | Ti-6Al-4V bar, AMS 4928, annealed, under 0.500 in, S-basis | Commercially pure, AMS 4902 sheet and plate (40 ksi yield class), annealed, S-basis |
|---|---|---|
| Ultimate tensile strength, Ftu (ksi) | 135 | 50 |
| Tensile yield strength, Fty (ksi) | 125 | 40 |
| Elongation (%) | 10 | 20 |
| Tensile modulus, E (10³ ksi) | 16.9 | 15.5 |
| Density (lb/in³) | 0.160 | 0.163 |
| Hardenable by heat treatment | Yes, solution treated and aged (STA) | No |
How does Grade 2 titanium compare with Grade 5?
Grade 2 is unalloyed titanium (UNS R50400 per ASTM B348) and in the 40 ksi yield class it has about one third of the yield strength of annealed 6Al-4V, but twice the elongation and almost the same density.
The 40 ksi class is how aerospace sheet buyers order it: AMS 4902 is titled for commercially pure, annealed sheet, strip and plate with 40.0 ksi yield strength, and that is the class commonly sold as Grade 2. Per MIL-HDBK-5J, commercially pure titanium cannot be hardened by heat treatment, so the strength on the certificate is the strength the part will have.
Per ASTM B348, there is also Grade 2H, a Grade 2 with a 58 ksi minimum tensile strength, listed in the standard’s scope. If a drawing says only “titanium”, a supplier can legitimately quote any of these, so name the grade.
Which grade should a machined part use?
Use Ti-6Al-4V when strength, fatigue or weight drives the design, and Grade 2 when the part is formed, welded or exists mainly for corrosion resistance.
The handbook comments explain the split. Per MIL-HDBK-5J, unalloyed titanium has been used primarily where strength is not the main requirement and is noted for excellent formability and ready weldability, while Ti-6Al-4V is weldable with established titanium techniques and the handbook recommends stress-relief annealing after welding. For a solid part machined from bar with no welding, the strength advantage of Grade 5 usually decides it; for a thin formed or welded shell, Grade 2 often does.
| If the part needs | Lean toward | Why |
|---|---|---|
| Highest strength or fatigue life at low weight | Ti-6Al-4V | About three times the yield of the 40 ksi CP class |
| Heavy forming or bending at room temperature | Grade 2 | Supplied annealed with excellent formability |
| Welded fabrication without post-weld heat treatment | Grade 2 | Readily welded; 6Al-4V welds call for stress relief |
| Salt-water service under sustained stress | Ti-6Al-4V | On the NASA high-resistance list for stress corrosion in all conditions; commercially pure grades are not listed in that table |
| Service up to the hot end of the range | Ti-6Al-4V | Handbook use range runs to 750 °F without loss of ductility |
What temperatures and environments can Ti-6Al-4V handle?
Per MIL-HDBK-5J, Ti-6Al-4V has a useful temperature range of -320 to 750 °F and can take prolonged exposure at 750 °F without loss of ductility.
For colder service, per MIL-HDBK-5J a special low-interstitial grade is usable down to -423 °F; ASTM B348 lists it as Grade 23 (6Al-4V ELI). For commercially pure titanium, per MIL-HDBK-5J there is a risk of embrittlement from oxygen, nitrogen and hydrogen pickup above 1050 °F.
On corrosion, MSFC-STD-3029A puts Ti-6Al-4V in all conditions in its table of alloys with high resistance to stress corrosion cracking in sodium chloride environments. MIL-HDBK-5J adds one caution that belongs on assembly drawings: in contact with cadmium, silver, mercury or some of their compounds, titanium can become embrittled. That rules out cadmium-plated fasteners and silver-plated hardware against titanium parts unless the combination has been cleared.
Does Ti-6Al-4V need heat treatment after machining?
Not usually: most machined parts are bought and used in the annealed condition, and solution treating and aging (STA) is called out only when the design needs the extra strength.
Per MIL-HDBK-5J, annealed or duplex-annealed material gives the best toughness, while STA gives the highest strength. Per MIL-HDBK-5J, the STA cycle for bar is a solution treatment at 1700 °F for 1 hour with a water quench, then aging at 1000 °F for 3 hours. A water quench moves thin features, so an STA part is normally roughed, heat treated and then finish machined, and the drawing should say which condition the finished part is in.
If stress relief is wanted after heavy machining, write it as a separate note with the specification you accept, rather than leaving the supplier to guess whether “annealed” on the material line also applies to the finished part.
How should titanium be written on the drawing and RFQ, and can Saola quote it?
Write the grade, condition and product specification together, such as “Ti-6Al-4V (Grade 5) bar per ASTM B348, annealed”, and send it for review; titanium is not on the bar material list of our CNC turning page, so whether and where a titanium part can be made is confirmed at drawing review.
A complete material block names the grade by number, not just “Ti”; the specification (ASTM B348 for bar, ASTM B265 for plate, or an AMS number for aerospace work); the condition; and whether a material certificate is required. Material certification is available on request, and new parts get a first-article inspection report. Our in-house work at the lead plant is CNC turning and CNC milling, and the review will say plainly if a titanium job is outside what the plant can take.
Add any finishing note in full. Titanium is often left bare; if a coating, anodize color or passivation is wanted, it must be raised at the same review, because finishes run from a fixed managed menu.
Frequently asked
Is Grade 5 the same as Ti-6Al-4V?
Yes. ASTM B348 lists Grade 5 as UNS R56400, titanium alloy with 6 percent aluminum and 4 percent vanadium. Grade 23 is the extra-low-interstitial version of the same alloy.
Is titanium lighter than aluminum?
No. Per MIL-HDBK-5J, Ti-6Al-4V has a density of 0.160 lb/in³ against 0.101 lb/in³ for 7075 aluminum; titanium saves weight only where its higher strength lets the part get thinner.
Can Grade 2 be heat treated to get stronger?
No. Per MIL-HDBK-5J, commercially pure titanium cannot be hardened by heat treatment; it can be annealed and stress relieved only. Pick a stronger grade instead.
Why do titanium threads seize?
Titanium has a strong tendency to gall against itself and other metals. The fixes are coatings, lubricants and mating material choices, covered in our galling guide.
Is Ti-6Al-4V safe in salt water?
For stress corrosion, NASA MSFC-STD-3029A rates it highly resistant in sodium chloride environments in all conditions. MIL-HDBK-5J calls it marginally susceptible in aqueous chloride but good compared with other common alloys.
Sources
- MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures, chapter 5 (titanium), US Department of Defense, 31 January 2003
- ASTM B348/B348M-21, Standard Specification for Titanium and Titanium Alloy Bars and Billets (scope), ASTM International, 2021
- MSFC-STD-3029A, Guidelines for the Selection of Metallic Materials for Stress Corrosion Cracking Resistance in Sodium Chloride Environments, NASA Marshall Space Flight Center, 24 February 2005
- AMS4902M, Titanium Sheet, Strip, and Plate, Commercially Pure, Annealed, 40.0 ksi (276 MPa) Yield Strength (catalog entry), SAE International, March 2023
- ASTM B265-20a, Standard Specification for Titanium and Titanium Alloy Strip, Sheet, and Plate (scope), ASTM International, 2020