Guide
What is the modulus of elasticity of steel, aluminum and titanium, and why does it matter for a machined part?
The modulus of elasticity is the constant ratio between stress and strain in the straight, elastic part of a material's stress-strain curve, so it tells you how far a part bends or stretches under a load before anything yields. Short answer: per MIL-HDBK-5J, carbon and low-alloy steels sit at about 29.0 x 10³ ksi (roughly 200 GPa), 6061 aluminum at 9.9 x 10³ ksi (about 68 GPa) and Ti-6Al-4V at 16.0 to 16.9 x 10³ ksi (about 110 to 117 GPa) depending on product form, so at the same geometry an aluminum part deflects close to three times as much as a steel one, whatever its strength.
By Saola Manufacturing engineering team · Published · Updated
Strength, grade choice and heat treatment for titanium are covered in Ti-6Al-4V properties, and why thin aluminum walls move after machining in thin-wall aluminum machining distortion. This page is about stiffness only: the modulus values, what changes them and what does not, and how to carry a stiffness requirement onto a drawing and into an RFQ.
On this page
What modulus of elasticity do steel, aluminum, titanium and brass have?
Steel is the stiffest of the common machined metals, titanium is a little over half as stiff, copper alloys sit close to titanium, and aluminum is about one third as stiff as steel. The table gives the handbook and association values.
The tension modulus E, the compression modulus Ec, the shear modulus G and Poisson's ratio come from the design property tables of MIL-HDBK-5J for the steels, aluminum alloys and titanium, and from the Copper Development Association data sheets for the copper alloys (MIL-HDBK-5J; CDA, C36000). The GPa column is a straight unit conversion from the ksi values, rounded. Values for one alloy family barely move between grades: the handbook gives one E for all of AISI 4130, 4135 and 8630 in its low-alloy steel table.
| Material | E, 10³ ksi | E, GPa (converted) | G, 10³ ksi | Poisson's ratio | Density, lb/in³ |
|---|---|---|---|---|---|
| AISI 1025 carbon steel | 29.0 | 200 | 11.0 | 0.32 | 0.284 |
| AISI 4130 / 4135 / 8630 low-alloy steel | 29.0 | 200 | 11.0 | 0.32 | 0.283 |
| 15-5PH stainless, H900 to H1150 | 28.5 | 197 | 11.2 | 0.27 | 0.283 |
| 6061 aluminum plate | 9.9 | 68 | 3.8 | 0.33 | 0.098 |
| 7075 aluminum sheet and plate | 10.3 | 71 | 3.9 | 0.33 | 0.101 |
| Ti-6Al-4V sheet, strip and plate | 16.0 | 110 | 6.2 | 0.31 | 0.160 |
| Ti-6Al-4V bar, annealed | 16.9 | 117 | 6.2 | 0.31 | 0.160 |
| C36000 free-cutting brass | 14.0 | 97 | 5.3 | not listed | 0.307 |
| C11000 copper | 17.0 | 117 | 6.4 | not listed | see data sheet |
Why does stiffness, not strength, decide how much a thin part deflects?
Below the proportional limit, deflection depends only on the load, the geometry and the modulus. Yield strength only tells you when the part stops springing back, so a stronger alloy with the same modulus bends exactly as far under the same load.
MIL-HDBK-5J defines E as the constant ratio of stress to strain on the initial straight line of the stress-strain curve, valid up to the proportional limit (MIL-HDBK-5J, Section 1.4.4.1). Every bending deflection formula you use for a bracket, a cantilevered tab, a long boring bar or a thin flange divides by E times the second moment of area of the section. Two consequences follow for machined parts.
First, a part that is strong enough can still fail its job by deflecting too much: a sensor arm that sags, a cover that rattles, a fixture plate that lets the workpiece move, or a shaft whose bending throws a bearing out of line. Second, geometry is the bigger lever. The second moment of area of a flat section grows with the cube of its thickness, so a small increase in wall or web thickness, or a rib, adds far more stiffness than any change of grade within the same metal.
Stiffness also matters during machining. A thin wall or a long, slender feature deflects under cutting force, so the tool removes less material where the feature springs away and the measured size drifts. Low-modulus materials show this sooner, which is one reason the thin-wall guide linked above recommends supports and light finishing passes.
Does heat treatment or a stronger grade change the modulus of elasticity?
Not in any way that matters for design. Heat treatment and alloy grade change strength and hardness a great deal, but the modulus of a metal family stays essentially fixed.
The handbook tables show this directly. For 15-5PH stainless, MIL-HDBK-5J lists conditions from H900 to H1150, with very different strengths, and gives the single modulus of 28.5 x 10³ ksi for all of them; the low-alloy steel tables give 29.0 x 10³ ksi both for normalized and tempered 4130 and for quenched and tempered 4130 tubing (MIL-HDBK-5J, Tables 2.3.1.0(c1), 2.3.1.0(c2), 2.6.7.0(b)). The same handbook gives about the same E for 6061 and 7075, which is why the 6061 vs 7075 comparison warns that 7075 does not fix a part that bends too much in 6061.
Two exceptions are worth knowing. Heavy cold work can make the modulus direction-dependent: for cold-rolled AISI 301 stainless sheet the handbook lists a longitudinal E of 29.0 x 10³ ksi annealed but 26.0 x 10³ ksi in the half-hard to full-hard tempers, per MIL-HDBK-5J Table 2.7.1.0(b). And the modulus falls as temperature rises; the handbook gives curves of modulus against temperature for low-alloy steels and other alloys, which should be read for any part that runs hot.
What happens to a part when you switch it from steel to aluminum or titanium?
At the same geometry, deflection scales with the ratio of the two moduli: an aluminum copy of a steel part bends close to three times as far, and a titanium copy almost twice as far. To get the stiffness back you have to change the section, not the grade.
Using the MIL-HDBK-5J values, 29.0 divided by 9.9 gives a ratio of about 2.9 between steel and 6061, and 29.0 divided by 16.0 gives about 1.8 between steel and Ti-6Al-4V sheet. For a plate or flat tab in bending, stiffness goes with E times thickness cubed, so matching the steel part in 6061 needs the thickness multiplied by the cube root of 2.9, about 1.43. The weight still falls, because 6061 is roughly one third the density of steel in the same table, and that is why aluminum often wins on stiffness per pound even though it loses on stiffness per part.
The ratio of modulus to density is close to the same for steel, 6061 and Ti-6Al-4V in the handbook values, so for pure axial stiffness none of the three saves much weight. The gains come in bending, where a thicker light-metal section benefits from the cube law. When you redesign, check four things: deflection at the critical load, clearance to mating parts once the walls grow, thread engagement in the softer metal, and the fastener and bearing-seat stiffness that the old steel part used to provide.
Brass sits between aluminum and titanium, while copper is about as stiff as titanium. With C36000 at 14.0 x 10³ ksi per the CDA data sheet, a brass fitting is roughly half as stiff as a steel one of the same shape, which matters for thin-walled fittings that get clamped or torqued.
How do you put a stiffness requirement on the drawing and in the RFQ?
Call the alloy, temper and material specification as usual, then state stiffness as a functional requirement: a load, a support condition and a maximum deflection. Do not write a modulus value on the drawing as an acceptance requirement.
Modulus is a property of the alloy family, not something a supplier controls or a mill certificate reports, so a minimum-modulus note copied from a data sheet cannot be bought or inspected. What the supplier can control is the material, the geometry and the tolerances that set the section. A useful set of entries looks like this:
- Material callout with specification, for example the steel grade and its bar specification, so the alloy family and therefore the modulus are fixed.
- Tolerances on the dimensions that drive stiffness: wall and web thickness, rib height, and the length of any cantilevered feature. A thickness at the low end of its tolerance reduces bending stiffness more than its share, because of the cube law.
- If stiffness is critical, a deflection test note on the drawing: fixture, load point, applied load and the maximum allowed deflection, plus how many parts per lot are tested.
- In the RFQ, a line saying the part is stiffness-critical and which feature carries the load, so the supplier does not suggest a material substitution with a lower modulus.
How do you check stiffness on machined parts you receive?
Confirm the material from its certificate, measure the dimensions that set the section, and run the deflection test only where the drawing calls for one. Hardness does not tell you the modulus.
Because the modulus of a given alloy family hardly varies, the practical risks are a wrong material and a thin section. The material certificate against the ordered specification covers the first. The second is a dimensional check of wall thickness, web thickness and feature length on the first article and at the lot sampling rate. A hardness check is still useful to confirm a temper or heat treatment, but a part at the wrong hardness has the same stiffness, and a part at the right hardness can still be too flexible if its walls are thin.
Where a deflection test is specified, agree the fixture early. Small differences in how the part is clamped change the measured deflection more than the material does, so the test fixture and the load point should be drawn or described, and the same fixture used at the supplier and at incoming inspection.
Can Saola machine stiffness-critical parts and check the dimensions that drive stiffness?
Yes for turned and milled parts within the capability pages; the grade and its specification are confirmed at drawing review, and the section dimensions are covered by the first-article and lot inspection records.
Turned parts run at our lead CNC plant in Vietnam on conventional CNC lathes, described on the CNC turning page; milled parts and second operations are on the CNC milling page. We make no general material claim here: the alloy, temper and specification on your drawing are confirmed at drawing review, and material certification is available on request. New parts get a first-article inspection report and every lot a dimensional inspection record, so wall and web thickness can be listed as characteristics. If your drawing carries a deflection test, send the fixture details with the drawing so it can be reviewed before quoting. Start through the quote form.
Frequently asked
Is Young's modulus the same as modulus of elasticity?
Yes. Young's modulus, elastic modulus and modulus of elasticity in tension all name E. The shear modulus G is a different constant, linked to E through Poisson's ratio for isotropic materials.
Is stainless steel less stiff than carbon steel?
Slightly, in the handbook values: 15-5PH is listed a little below the low-alloy steels. For most machined parts the difference is small next to the effect of geometry.
Why do two data sheets give different modulus values for the same alloy?
Test method, product form, direction and rounding all differ. For design, use one consistent source such as the MMPDS handbook series that replaced MIL-HDBK-5J, and note which one on the analysis.
Does anodizing or plating make an aluminum part stiffer?
Not in a useful way. A coating is thin compared with the part section, so the stiffness is still set by the base metal and the geometry.
Should I use the tension or compression modulus?
For bending, E is the usual choice. The handbook lists Ec separately because most common structural alloys are slightly stiffer in compression, so it is good practice to use Ec for compression members and buckling checks.
Sources
- MIL-HDBK-5J, Metallic Materials and Elements for Aerospace Vehicle Structures, U.S. Department of Defense, 2003 (Sections 1.4.4.1 and 1.4.6.1; Tables 2.2.1.0(b), 2.3.1.0(c1), 2.3.1.0(c2), 2.6.7.0(b), 2.7.1.0(b), 3.6.2.0(b2), 3.7.6.0(b4), 5.4.1.0(b), 5.4.1.0(c1))
- C36000 Free-Cutting Brass data sheet, Copper Development Association, archived May 2026
- C11000 Electrolytic Tough Pitch Copper data sheet, Copper Development Association, archived May 2026