Aluminum vs Stainless vs Titanium

The Short Answer

Weight matters (aerospace, moving robot axes, anything on a gantry) → titanium first, 6061 aluminium when budget rules.
Weight doesn't matter, corrosion or wear does → stainless, and it will usually be the cheapest of the three to machine.
Neither is critical → 6061-T6 aluminium. It is the default for a reason: cheapest stock, fastest to cut, easiest to finish.

The rest of this page is the reasoning, because the decision is rarely that clean.

Property	6061-T6 Aluminium	304 Stainless	316 Stainless	17-4PH Stainless	Ti-6Al-4V Titanium
Density (g/cm³)	2.70	8.00	8.00	7.80	4.43
Yield strength (MPa)	276	215	205	1,100	880
Tensile strength (MPa)	310	505	515	1,310	950
Specific strength (yield ÷ density)	102	27	26	141	199
Elastic modulus (GPa)	68.9	193	193	197	113.8
Thermal conductivity (W/m·K)	167	16.2	16.3	18	6.7
Max service temperature (°C)	~200	~870	~870	~315	~400
Corrosion resistance	Good (anodised)	Very good	Excellent (marine)	Good	Excellent
Relative material cost	1×	3–4×	4–5×	6–8×	10–20×
Relative machining time	1×	3–5×	3–5×	4–6×	5–10×
Machinability	Excellent	Moderate — work hardens	Moderate — work hardens	Difficult	Difficult — heat + reactivity
Biocompatible	No (usually)	Yes	Yes	Sometimes	Yes — excellent
Magnetic	No	No (annealed)	No (annealed)	Yes	No

Values are typical for the tempers shown and vary by supplier and heat treatment. Specific strength is yield strength divided by density — higher means more strength per unit of weight.

Custom stainless steel CNC machined shaft with turned flange base — typical 304/316 OEM shaft component — **Typical stainless 304/316 CNC part** — a precision shaft with turned and milled features. Stainless cuts three to five times slower than aluminium, which is why the finished part costs several times the bar price. See our stainless steel material page for grades and finishes.

Why Specific Strength Is the Number That Matters

Pull one figure out of that table: specific strength — yield strength divided by density.

Titanium scores about 199, 6061 aluminium about 102, and 304 stainless about 27. Read that as: for the same weight of material, titanium carries roughly twice the load of aluminium and over seven times the load of 304 stainless.

This is why the "titanium is strongest" claim is both true and misleading. Titanium's absolute yield (880 MPa) is actually lower than heat-treated 17-4PH stainless (1,100 MPa). Titanium wins on strength per kilogram, not strength per square millimetre.

So the first question isn't "how strong does it need to be" — it's "how strong does it need to be per kilogram?" If the part sits on a bench and never moves, the answer doesn't matter and stainless or aluminium will be far cheaper. If it's on the end of a moving robot arm, every kilogram you remove is payload you gain.

One at a Time

What Each Material Is Like on the Machine

6061-T6 aluminium — the default for a reason

Cuts fast, holds tolerance easily, takes a beautiful anodised finish, and costs the least per kilogram of the three. Thermal conductivity is high (167 W/m·K), so cutting heat leaves with the chip instead of cooking the tool.

Where it stops working: above roughly 200°C it loses a large share of its room-temperature strength. It's relatively soft, so bare aluminium galling and wear are real issues in sliding contact. And it needs anodising or plating for saltwater exposure.

We published a full comparison of the common aluminium grades if you've settled on aluminium and just need to pick the alloy.

304 and 316 stainless — cheap material, expensive machining

The trap here is that stainless stock is only three to five times the price of aluminium per kilogram, so it looks like a modest step up. It isn't, because the machining time is three to five times longer — so the finished part can cost several times more, not the three-fold the material price suggests.

Why it cuts slowly: austenitic stainless work-hardens rapidly. A tool that rubs instead of shearing makes the surface harder for the next pass, and it compounds. Combined with poor thermal conductivity (16 W/m·K, a tenth of aluminium), heat stays in the tool.

316 vs 304: 316 adds molybdenum, which is what makes it the right choice for marine and chloride environments. If your part isn't seeing saltwater or harsh chemicals, 304 is cheaper and machines the same.

17-4PH is a completely different animal — a precipitation-hardening grade that reaches 1,100 MPa yield after heat treatment. That's stronger than Ti-6Al-4V in absolute terms. It's used when you need very high strength without paying titanium prices, and you can tolerate the weight.

Ti-6Al-4V — excellent material, genuinely difficult to cut

Three things compound to make titanium slow and expensive on the machine:

It barely conducts heat — 6.7 W/m·K, about one twenty-fifth of aluminium. Cutting heat has nowhere to go except into the tool edge, which is why titanium destroys cutting tools.
It's chemically reactive at cutting temperature and can weld itself to the tool edge, then tear pieces out of it.
Low elastic modulus means the workpiece deflects away from the cutter under load, then springs back — you get chatter and rubbing instead of a clean shearing cut.

We wrote a full titanium machining guide covering speeds, tooling, tapping and the chip fire risk. What that means in practice: lower cutting speeds, rigid setups, sharp tooling changed early, and constant flood coolant. We run it regularly and it's perfectly manageable — just budget for the cycle time honestly. How machining cost is calculated covers why cycle time dominates the quote.

Where titanium earns its cost: aerospace structures, medical implants (it's the most biocompatible of the three), and anywhere the strength-to-weight ratio is the entire point of the design.

Decision Guide

Seven Questions That Pick the Material

Ask yourself	If yes
Is the part weight-critical or on a moving axis?	Titanium first, aluminium if budget rules
Does it run above 200°C in service?	Rule out 6061 — stainless or titanium
Is it implanted or in contact with body tissue?	Titanium, or 316 stainless
Seawater, chlorides or harsh chemicals?	316 stainless or titanium; anodised aluminium marginal
Sliding wear without surface treatment?	Stainless over bare aluminium
Non-magnetic required?	Rule out 17-4PH (it's magnetic)
None of the above applies?	6061-T6 — cheapest and fastest

Three Mistakes We See Repeatedly

1. Specifying titanium when aluminium would do

Titanium sounds like the premium, safe choice. But if the part isn't weight-critical, you've multiplied the cost of the part by five to ten for a property nobody is using. Ask what the weight saving actually buys you — if the answer is "nothing measurable," it's 6061.

2. Choosing stainless by material price alone

Stock price says stainless is 3–4× aluminium. Finished-part cost says several times more, because the cycle time is 3–5× longer. Budget on the machined part, not the bar.

3. Treating "stainless" as one material

304, 316 and 17-4PH differ enormously — 316 for chlorides, 17-4PH when you need 1,100 MPa yield, 304 for general use. Writing "stainless steel" on a drawing leaves the shop guessing, and they may quote a grade that doesn't suit the application.

FAQ

Material Selection Questions

Which is stronger: aluminium, stainless steel or titanium?

By absolute strength, heat-treated stainless such as 17-4PH and titanium Ti-6Al-4V both far exceed 6061 aluminium. But by strength-to-weight ratio, titanium leads at roughly twice 6061 aluminium and over seven times 304 stainless. If weight matters, compare specific strength, not absolute yield.

Why is titanium so expensive to machine?

Three compounding reasons. Titanium conducts heat poorly — about one twenty-fifth as well as aluminium — so cutting heat stays in the tool instead of leaving with the chip, which destroys tool edges. It is chemically reactive at cutting temperatures and can weld to the tool. And its low elastic modulus means the part deflects away from the cutter, causing chatter and rubbing instead of clean cutting.

Is stainless steel harder to machine than aluminium?

Yes, substantially. Austenitic grades like 304 and 316 work-harden rapidly, so a tool that rubs instead of cuts makes the surface harder for the next pass. They also conduct heat poorly compared with aluminium. Cycle times on stainless are commonly three to five times longer than the same geometry in 6061 aluminium.

When does aluminium stop being a good choice?

Above roughly 200 degrees Celsius, where 6061 loses a large share of its room-temperature strength, and in applications needing high wear resistance or galling resistance without surface treatment. It also needs anodising or plating for corrosion resistance in saltwater or harsh chemical environments.

Can I substitute stainless for titanium to save cost?

Only if weight is not a constraint. Stainless is denser and far lower in specific strength, so a stainless part designed to replace a titanium one will usually be much heavier for the same stiffness. Where the weight saving is the entire point, such as aerospace or a moving robot axis, the substitution does not work.

What about plastics — should I consider POM or PEEK?

Often, yes. Engineering plastics machine faster than any metal and weigh a fraction as much. POM (Delrin) is excellent for low-friction, dimensionally stable parts at room temperature, and PEEK handles high temperatures and chemical exposure with strength approaching some aluminium alloys. If loads are modest, plastic is frequently the cheapest answer. See our materials page for the full range we machine.

Which material is cheapest to machine overall?

By finished-part cost, 6061 aluminium is by far the cheapest — lowest material price, fastest cycle time, and easiest to hold tight tolerance. Stainless is several times more because machining time runs three to five times longer, even though the bar stock is only a few times dearer. Titanium is the most expensive by a wide margin: 10–20× the material cost and 5–10× the cycle time. The ranking is consistently aluminium, then stainless, then titanium.

Which is best for corrosion resistance and marine use?

316 stainless is the standard for marine and chloride environments, with titanium close behind and better for weight-critical parts. Aluminium resists corrosion well once anodised, but bare aluminium in seawater is a poor choice. For outdoor structural parts where weight does not matter, 304 or 316 stainless is the pragmatic pick; for weight-sensitive outdoor or marine parts, titanium earns its cost.

Not Sure?

Tell Us the Application, Not Just the Material

Send the drawing with a line about where the part lives — load, temperature, environment, whether it moves. We'll tell you if the specified material is right, over-specified, or wrong for the application, and quote alternatives side by side.

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Aluminium vs Stainless Steel vs Titanium