Aluminum vs Stainless Steel vs Titanium: Choosing Material for CNC Machined Parts
Published 28 October 2026 · 8 min read
Material choice is the single largest lever on machined part cost after tolerance, and it is usually decided early — often copied from a previous project without re-examination. The four families below cover the overwhelming majority of CNC work, and each has a characteristic failure mode when chosen for the wrong reason.
The comparison at a glance
| Property | Aluminum | Stainless | Titanium | Plastics |
|---|---|---|---|---|
| Density | ~2.7 g/cm³ | ~7.9 g/cm³ | ~4.4 g/cm³ | ~1.2–1.4 g/cm³ |
| Machinability | Excellent | Fair to poor | Poor | Good, but gummy |
| Corrosion resistance | Good (needs anodising) | Excellent | Excellent | Depends on grade |
| Relative raw cost | Low | Medium to high | Very high | Low, PEEK excepted |
| Tool wear | Low | Medium | High | Very low |
| Typical use | Housings, brackets, heatsinks | Medical, food, marine, fittings | Aerospace, high-load, aggressive environments | Insulators, prototypes, light loads |
Two things in that table are commonly underestimated. First, stainless is not "a bit harder" than aluminum — it work-hardens under the cut, so light spring passes that were meant to improve finish can actually make the surface harder and burnish the edge. Second, titanium's difficulty is not strength but heat: it conducts heat so poorly that cutting temperature stays at the tool edge and destroys it.
Aluminum: the default, and usually the right one
6061-T6 is the workhorse. Good strength, excellent machinability, welds and anodises predictably, and available in a wide range of bar and plate sizes. If a part does not have a documented reason to use something else, it is probably 6061.
7075-T6 is roughly twice the strength and noticeably worse to machine — it is gummier on the cutter and more dimensionally restless when a lot of material is removed from one side. Use it when yield strength genuinely drives the design, such as thin high-load brackets or robotics links, not as a default upgrade.
Stainless: choose the grade deliberately
304 is the general-purpose austenitic grade. Fine for most industrial parts, but it is susceptible to chloride stress cracking and is not ideal for regular washdown with chlorinated cleaners.
316L adds molybdenum, which is what buys the resistance to chlorides and marine environments. The L suffix means low carbon, which reduces carbide precipitation during welding. If a part will be welded and then used in a corrosive environment, 316L is the correct call rather than 304.
17-4PH is a precipitation-hardening grade used where high strength plus corrosion resistance are both needed — shafts, valve components, high-load fasteners. It is supplied in a condition that machines reasonably well and is then aged to final hardness, which means the heat-treat condition must be specified on the drawing, not assumed.
Titanium: pay for it only when it earns its place
Grade 5 (Ti-6Al-4V) dominates machined titanium. Its specific strength — strength per unit weight — is what justifies the cost, plus near-total immunity to corrosion in most environments. Both advantages matter in aerospace and in high-end motorsport or medical hardware.
In conventional industrial parts, titanium is rarely the right answer. It costs several times more in raw stock, machines at a fraction of aluminum's rate, consumes tooling quickly, and cannot be substituted casually once a design has been validated on it. If a previous project used titanium and a new one copied the callout, that is worth a second look.
Engineering plastics: often the omitted option
POM (Delrin) machines beautifully, holds tolerance well, and is dimensionally stable — a strong choice for insulators, wear pads and light-load mechanism parts. PEEK handles temperature and chemicals far beyond POM but costs an order of magnitude more, so it belongs only where those properties are actually required.
A short decision sequence
- Does the part carry load? If not, stop at aluminum or plastic and save the budget.
- Is weight critical? If yes, aluminum beats stainless on density before strength is even considered.
- Is the environment aggressive? Chlorides, washdown, marine, or body contact push toward 316L or titanium.
- Will it be welded? Then low-carbon grades matter, and post-weld corrosion behaviour matters more than raw strength.
- Is heat treatment involved? If yes, the condition must be on the drawing, because machinability changes with it.
How material choice shows up in your quote
Material affects price twice: once as raw stock, and again as machine time, because harder materials cut slower and wear tooling faster. A part that costs one unit of machine time in 6061 may cost two in 304 and three or more in titanium. That is why a "small material change" can move a quote by more than the material itself costs.
We machine all four families in-house — see the materials table on our precision CNC machining page — and if a drawing calls for a grade that will not machine as specified, we say so before quoting rather than after.
Frequently asked
Can I substitute 6061 for 7075 without telling anyone?
No. 7075 is roughly twice the yield strength of 6061. A part designed around 7075 may be under-designed in 6061, and a part designed around 6061 doesn't need 7075. The substitution has to be a design decision, not a purchasing one.
Is anodising required on all aluminum parts?
Not all, but most exposed parts benefit. Bare aluminum oxidises into a soft, uneven film that marks easily. Anodising gives a controlled, harder surface and allows colour. Internal, non-visible parts often run bare.
Why is titanium machining so much more expensive?
Low thermal conductivity keeps heat at the cutting edge, so tools wear fast and feeds must be reduced. It also work-hardens and is chemically reactive at temperature. The result is much lower material removal rate per hour plus higher tooling consumption.
Does material affect achievable tolerance?
Yes. Aluminum moves more with temperature change than steel, so a ±0.01mm callout on a large aluminum part requires temperature-controlled measurement. Titanium is stiffer but springier under cut, so thin walls deflect more during machining.
Not sure which grade fits your part?
Send the drawing and application. We will tell you what the material needs to do and what it will cost, before you commit.
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