Aluminium is the easiest common metal to cut and one of the hardest to hold to size. Stock stress, cycle heat and the anodise layer each move a finished dimension. Mecvona machines six stocked alloys and anodises in house, so that movement is planned into the toolpath instead of discovered at your incoming inspection.
Aluminum CNC machining is the subtractive manufacture of parts from wrought or cast aluminium alloy, cutting away material with rotating tools until the finished geometry remains. Aluminium is the most machined metal in the world because it cuts three to five times faster than steel, weighs about a third as much, conducts heat and electricity well, and takes an anodised finish that is both protective and decorative.
Cutting speed keeps unit cost low, especially on high-speed spindles where aluminium tolerates aggressive material removal. A density of 2.70 g/cm³ against steel’s 7.85 makes it the default wherever weight matters. The natural oxide layer resists corrosion with no coating at all, and anodising thickens that layer into a hard, dyeable surface.
The difficulty is not the cutting. Because aluminium is soft and thermally active, the hard part is keeping the component the size you cut it to. Residual stress in the stock, heat generated during the cycle, and the thickness added by anodising each move a finished dimension after the cutter has left. That is where almost every aluminium quality problem originates, and it is what the rest of this page is about.
Most alloy tables list mechanical properties and leave the decision to you. Pick what your part is actually judged on and Mecvona will name the alloy we would quote, why, and the trade-off that comes with it.
Choose the dominant requirement
Mecvona would quote
The default for good reason. It machines cleanly with a well-broken chip, welds, resists corrosion without coating, heat treats, and anodises to a consistent finish that takes dye evenly. For the large majority of housings, brackets, plates and fixtures there is no reason to pay for anything else.
Trade-off: about half the yield strength of 7075-T6. If the part is highly loaded rather than simply structural, move up.
Yield strength of 503 MPa against 276 MPa for 6061-T6, with excellent fatigue resistance. This is the alloy for highly loaded structural parts, aerospace fittings, tooling plates and motorsport hardware where every gram is being justified.
Trade-off: lower corrosion resistance, poor weldability, 20–40% higher machining cost, and it anodises darker with a yellow cast. Not the choice for a visible cosmetic surface.
Alloy chemistry decides how anodising looks. The 6000 series anodises to a clean, even layer that accepts dye consistently — which is why almost every anodised consumer product you have handled is a 6000-series alloy.
Avoid: 2024 and ADC12 for visible surfaces. Copper and silicon content disrupt the oxide layer and produce patchy, uneven colour that process control cannot fully correct.
Outstanding resistance to saltwater and chemical attack, retains toughness at cryogenic temperatures, and welds well. The standard choice for marine hardware, offshore equipment, pressure vessels and cryogenic components.
Trade-off: gummier in the cut than 6061, so cycle times are longer and the surface finish needs more attention. It anodises bright and even.
Rolled plate carries residual stress that releases when material is removed asymmetrically, bowing the part after it leaves the fixture. Cast tooling plate arrives stress-relieved, which is why it is the standard for machine tables, optical mounts and large flat parts held to tight flatness.
Alternative: where 6061 is specified, the T651 temper is stretch-relieved and we rough, allow the part to relax, then finish. Both approaches are stated in the quote.
At volume the material price difference between common alloys is small compared with machine time, and 6061 cuts faster and cleaner than the higher-strength grades. Choosing it over 7075 usually saves more in cycle time and tool life than in stock cost.
Bigger lever: on an aluminium part, geometry drives cost far more than alloy. Opening non-functional tolerances and widening deep pockets will save more than any material substitution.
Mechanical properties matter, but so does how an alloy behaves in the shop and how it looks after anodising
| Alloy | Yield | Hardness | Machinability | Anodised appearance | Best for |
|---|---|---|---|---|---|
| 6061-T6 | 276 MPa | 95 HB | Excellent, clean chip | Clear and consistent, slight grey | The default. Housings, brackets, manifolds, fixtures |
| 6082-T651 | 260 MPa | 95 HB | Excellent | Good, close to 6061 | European equivalent of 6061, structural work |
| 7075-T6 | 503 MPa | 150 HB | Good, short chip | Acceptable, darker with a yellow cast | Highly loaded structure, aerospace fittings, tooling |
| 2024-T351 | 325 MPa | 120 HB | Good | Poor cosmetically — copper causes patchiness | Fatigue-critical aerospace parts, usually clear-coated not anodised |
| 5083-H111 | 228 MPa | 75 HB | Fair, gummy chip | Bright and even | Marine, cryogenic, pressure vessels, welded assemblies |
| ADC12 (A380) | 160 MPa | 80 HB | Fair, abrasive silicon | Uneven dark grey — not for decorative use | Machining of die-cast housings and covers |
These two account for most aluminium enquiries we receive. 7075 is stronger; that is the only category where it wins outright.
| 6061-T6 | 7075-T6 | |
|---|---|---|
| Yield strength | 276 MPa | 503 MPa |
| Relative machining cost | 1.0× | 1.2 – 1.4× |
| Corrosion resistance | Good, usable uncoated | Lower, needs coating outdoors |
| Weldable | Yes | No, not practically |
| Anodised appearance | Clean and even, takes dye well | Darker with a yellow cast |
| Choose it when | The part is structural, visible, welded or cost-driven | Load or weight is the binding constraint |
If your part is not weight-critical, 6061-T6 is almost always the better commercial answer. Where a drawing specifies 7075 out of habit rather than calculation, Mecvona will say so and quote both.
When an aluminium part fails inspection, it is rarely because the machine could not cut the feature. It is because the part changed shape afterwards — on the fixture, on the bench, or in the anodising tank.
Rolled plate and extruded bar are locked in tension and compression from the moment they leave the mill. As long as the material is symmetric, those forces balance. Machine a deep pocket on one side and the balance breaks — the part bows, sometimes visibly, usually after it comes off the fixture and the clamps stop holding it flat.
The fix is process, not machine. Rough with generous stock left on, allow the part to relax, then finish. For flatness-critical plates we can specify stress-relieved cast tooling plate instead of rolled plate, which arrives with the stress already removed. Tell us if flatness across a large face is functional and we plan the sequence around it rather than quoting a single-pass cycle that will not hold.
Aluminium expands roughly 23 µm per metre per °C — about twice as much as steel. On a 200 mm part, a 10 °C rise between roughing and final measurement is 46 µm of growth, which is several times a tight tolerance band. High-speed machining puts real heat into a part, and the part gives it back slowly.
Mecvona schedules finishing passes after the part has stabilised and measures at controlled temperature rather than straight off the spindle. Where a bore is held tighter than ±0.02 mm, flag it — knowing which dimension is thermally critical changes how the cycle is written.
Anodising is not a coating applied on top of the metal. It converts the surface into aluminium oxide, and that oxide occupies more volume than the metal it replaced. Roughly half the coating thickness grows outward from the original surface; the other half grows inward.
An external diameter therefore grows, an internal bore shrinks, and a hardcoated thread can stop accepting a standard fastener. This is the single most common reason an aluminium part passes inspection at the machine shop and fails at the customer.
A shaft gets bigger. A bore gets smaller. A thread may stop fitting. None of this is a defect — it is how the process works, and it has to be in the drawing or in the quote.
As a working rule, about half the anodic coating thickness grows outward from the original machined surface. Because an external diameter grows on both sides, the diameter increases by roughly the full coating thickness. An internal bore shrinks by the same amount.
| Anodising type | Typical coating | Growth per surface | Effect on a diameter | Typical use |
|---|---|---|---|---|
| Type II — sulfuric | 5 – 25 µm | 2.5 – 12.5 µm | ±0.005 – 0.025 mm | Standard protection, dyed colours, most enclosures |
| Type III — hardcoat | 25 – 75 µm | 12.5 – 37.5 µm | ±0.025 – 0.075 mm | Wear surfaces, hydraulic bores, aerospace hardware |
| Chromate conversion | < 1 µm | Negligible | No allowance needed | Corrosion protection where conductivity must be retained |
An external diameter grows by roughly the full coating thickness and an internal bore shrinks by the same amount, because about half the coating grows outward from the original machined surface. Mecvona machines critical features with that allowance subtracted and states in every quote whether your tolerance applies before or after finishing.
Because anodising runs in our own plant rather than at a subcontractor, the allowance is a machining decision rather than a negotiation after the fact. Three things happen as standard:
All of these are available on Mecvona aluminium parts. Read the dimensional column before you specify a tight tolerance on a finished surface.
| Finish | What it does | Dimensional effect | Colour options |
|---|---|---|---|
| As machined | Visible tool marks, lowest cost, tightest achievable tolerance | None | Natural aluminium |
| Bead blasting | Uniform matte texture, hides tool marks, common before anodising | Under 0.010 mm | Natural, matte grey |
| Anodising Type II | Corrosion and wear resistance, dyeable, electrically insulating | 0.005 – 0.025 mm | Clear, black, red, blue, gold and custom |
| Anodising Type III | Thick hardcoat for wear surfaces, much harder than Type II | 0.025 – 0.075 mm | Clear to dark grey, black; colour range limited |
| Chromate conversion | Corrosion protection that stays electrically conductive | Negligible | Clear or gold |
| Brushing | Directional satin grain, cosmetic, often followed by anodising | Under 0.010 mm | Natural |
| Polishing | Reflective surface for cosmetic or optical use | Varies with stock removal | Bright natural |
| Powder coating | Thick, durable, UV-stable colour layer | 0.050 – 0.150 mm | Full RAL and Pantone range |
Anodising, bead blasting, brushing and polishing run inside Mecvona’s own plant, which is why the dimensional allowance is set at programming rather than negotiated after the fact. Powder coating and specialist plating run on qualified partner lines, inspected on return.
Every figure is given in metric and imperial because drawings arrive in both.
±0.010 mm is what a single controlled feature can be held to. ±0.025 mm is what arrives at your incoming inspection lot after lot at Cpk ≥ 1.33. ISO 2768-m is what applies to any dimension your drawing does not call out specifically. On aluminium there is a fourth question that matters as much as any of them — whether the tolerance is measured before or after anodising. The quote names all four rather than publishing a single headline figure.
Aluminium rewards high surface speed with a better finish and lower cutting force. Dedicated high-speed machines run it at feed rates that would destroy a tool in steel, which is where most of the cost advantage comes from.
Polished-flute, high-helix cutters and through-tool coolant stop the long stringy chips aluminium produces from re-cutting and scarring a finished surface — the most common cause of cosmetic rejects.
Gantry and horizontal machines take aluminium plates and frames up to 1200 × 600 × 500 mm in one setup, which matters more on aluminium than most metals because large plates are exactly what warps.
Six notes we send back to engineers most often on aluminium prints. Handling them at the drawing stage is free; handling them at first article is not.
This is the single most valuable line you can add to an aluminium drawing. A Ø20 H7 bore is a different part depending on whether it is measured as machined or after hardcoat. If the print is silent we will ask, but stating it removes a round trip and any risk of the wrong assumption being priced.
We machine down to 0.5 mm, but below roughly 0.8 mm a wall starts to vibrate away from the cutter, which costs finish quality and cycle time. Adding a rib or a small radius at the base of a tall thin wall usually buys back more than the material it costs.
Every internal vertical corner takes the radius of the cutter. A generous radius lets us use a larger, stiffer tool at higher feed. A sharp internal corner is not a milling feature at all — it needs EDM, quoted as a separate operation.
Past that, the tool chatters, the finish degrades and cycle time climbs sharply. Widening a pocket by a couple of millimetres so a larger cutter fits often removes an entire cost tier, and on aluminium the material saving is negligible either way.
Residual stress in rolled plate will bow a part once material is removed asymmetrically. If a face must stay flat, we rough, allow the part to relax and then finish — or specify stress-relieved cast tooling plate instead. Both change the quote, and both are cheaper than a rejected lot.
Anodising is an electrical insulator. Earth points, connector seating faces, press-fit bores and bearing seats all need masking, plugging or a chromate finish instead. Marking those features on the drawing is the difference between a part that assembles and a part that arrives non-conductive where it needed to conduct.
Aluminium cuts easily, so quotes look cheap and expectations run high. Raw material is rarely the largest line — stock is inexpensive relative to the machine time spent removing it, which is why the cost conversation is almost always about geometry, setups and finishing rather than about the metal.
Indicative multipliers against a baseline part in 6061-T6, as-machined, ISO 2768-m. Real numbers depend on your geometry, but the relative weight of each decision holds.
| Decision | Effect on part price | Worth it when |
|---|---|---|
| 6061-T6 → 7075-T6 | +20 – 40% | Load or weight is the binding constraint |
| ISO 2768-m → ±0.01 mm on all features | +40 – 80% | Almost never. Mark only the features that carry function |
| Adding Type II anodising | +10 – 20% | Corrosion protection or colour is required |
| Type II → Type III hardcoat with masking | +25 – 45% | The surface wears, or a specification calls it out |
| Pocket depth 5× → 10× tool diameter | +30 – 60% | Rarely. Widening the pocket is usually cheaper |
| Adding a stress-relief sequence | +15 – 25% | Flatness across a large face is functional |
Indicative multipliers against a baseline part in 6061-T6, as machined, to ISO 2768-m. Real numbers depend on your geometry, but the relative weight of each decision holds.
Each re-fixturing adds machine time, handling and an inspection gate. A part with features on four faces costs far less on a machine with a rotary axis than on a three-axis machine run four times.
Tight tolerances mean slower finishing passes, more in-process measurement and lower yield. A blanket tight tolerance multiplies all three.
These force small tools, shallow cuts and long cycles. This is usually the largest avoidable cost on an aluminium part.
Hardcoat anodising with masked threads and bores is a real operation with real handling. It belongs in the quote as its own line, not folded invisibly into the part price.
Setup and programming amortise across the lot. Four releases of 250 is a different job from one order of 1,000.
Read the table together and the pattern is clear: a simple aluminium part is one of the cheapest precision components you can buy, while the same part with blanket tolerances, deep narrow pockets and a masked hardcoat finish can cost three times as much. Almost all of that difference is designed in rather than quoted in, which is why the DFM notes returned with every Mecvona quote name the specific features driving your number.
On aluminium, when a part is measured matters as much as how. A dimension checked warm off the spindle, or checked before anodising when the print applies afterwards, is not a dimension you can rely on.
Three things are done differently on aluminium, and each of them exists because of a specific way aluminium parts go wrong.
Aluminium expands about twice as much as steel per degree. Parts reach controlled temperature before dimensional inspection rather than being checked straight off the spindle, where a 200 mm part can read tens of microns oversize.
Where your print applies after anodising, the first article is inspected after anodising — not before, with an allowance assumed. Coating thickness is verified on the same parts so the growth can be reconciled against the dimension.
On flatness-critical plates, the part is measured off the fixture rather than clamped. A stressed plate reads flat while it is held down and bows the moment the clamps come off.
Dimensional inspection runs on a Mitutoyo 4078M-1211 CMM against the datum scheme on your drawing, with coating thickness gauges, surface roughness, hardness, salt spray and XRF for RoHS available alongside. Adhesion and corrosion testing on anodised surfaces are available where the specification calls for them.
What ships with the parts: mill certificates traceable to the aluminium supplier, dimensional reports, FAI in AS9102 format, PPAP to your required level, anodising certificates stating measured coating thickness, and RoHS and REACH declarations. Records are retained three years and traceable to lot, machine and anodising batch — the last of which matters when a colour has to be matched across a repeat order.
Mecvona holds IATF 16949:2016, AS9100D, ISO 14001:2015 and ISO 10012 measurement management. Customer audits are welcome, on site or remote.
A print alone gets you a price. These six get you a price, an alloy recommendation, and the notes that change the number.
The model lets us check tool access and wall thickness; the print carries the tolerances and the datum scheme.
If you are not fixed on a grade, tell us the loading, the environment and whether it is visible. We will name the alloy and say why.
Type II or Type III, colour, and which features must stay masked. This is the most common gap on aluminium enquiries.
It decides whether we plan a stress-relief sequence or specify cast tooling plate instead of rolled plate.
A visible surface is inspected by eye as well as by gauge. Naming those faces changes tooling, finishing sequence and how the parts are packed.
Four releases of 250 prices differently from one order of 1,000. Name the FAI format, PPAP level and whether you need coating thickness reports.
A Mecvona engineer sends a DFM response within one business day: the alloy we would use, whether the tolerance is achievable as machined or needs an anodising allowance, the features driving the price, and questions where the print is ambiguous rather than assumptions built quietly into the number.
6061-T6 is the default and the right answer for most parts — it machines cleanly, welds, resists corrosion and anodises to a consistent finish. Choose 7075-T6 when strength-to-weight governs, 5083 for marine and cryogenic service, 2024-T351 for fatigue-critical aerospace parts, and 6082-T651 where a European structural equivalent to 6061 is specified. Mecvona stocks all of these plus ADC12 for machining die-cast housings.
Yes. Anodising converts the surface into aluminium oxide, which occupies more volume than the metal it replaced. Roughly half the coating thickness grows outward, so an external diameter increases by about the full coating thickness and an internal bore shrinks by the same amount. Type II anodising typically changes a diameter by 0.005–0.025 mm; Type III hardcoat by 0.025–0.075 mm. On a Ø20 H7 bore, hardcoat can consume more than twice the entire tolerance band, which is why Mecvona machines critical features with the growth subtracted and states in the quote whether your tolerance applies before or after finishing.
Mecvona holds ±0.010 mm (±0.0004″) on a single controlled feature and ±0.025 mm (±0.001″) across a production lot at Cpk ≥ 1.33. Dimensions with no specific callout default to ISO 2768-m. Surface finish is Ra 0.4–1.6 µm as machined. On aluminium a fourth question matters as much — whether the tolerance is measured before or after anodising — and the quote names it explicitly.
Rolled plate and extruded bar carry residual stress from the mill. While the material is symmetric those forces balance; removing material from one side breaks the balance and the part bows, usually once it comes off the fixture. Heat is the second cause — aluminium expands about 23 µm per metre per °C, roughly twice as much as steel, so a warm part measures larger than a cool one. Mecvona roughs with stock left on, allows the part to relax before finishing, and can specify stress-relieved cast tooling plate where flatness across a large face is functional.
6061, 6082, 6063 and 5083 anodise to a clean, even finish and take dye consistently. 7075 anodises acceptably but darker, with a yellow cast from the zinc content. 2024 is poor cosmetically because its high copper content disrupts the oxide layer and produces patchy results. Cast ADC12 anodises unevenly to a dark grey because of its silicon content and is normally painted or powder coated instead. If a part is both structural and visible, that trade-off is worth raising at enquiry.
1200 × 600 × 500 mm on our gantry and horizontal machining centres, and Ø150 mm on the turning and turn-mill side. Minimum wall thickness is 0.5 mm subject to geometry, minimum end mill diameter 0.5 mm, and pocket depth up to about ten tool diameters before finish and cycle time degrade sharply.
Usually, yes — aluminium cuts three to five times faster than steel and the stock costs less per part for most geometries, so machine time drops sharply. The exception is a part with blanket tight tolerances, deep narrow pockets or a hardcoat finish with extensive masking, where finishing and process control can cost more than the machining. On an aluminium part, the cost is designed in far more than it is quoted in.
As machined, bead blasting, brushing, polishing, chromate conversion, and anodising in Type II and Type III with a full colour range. Anodising, bead blasting, brushing and polishing run inside Mecvona’s own plant; powder coating and specialist plating run on qualified partner lines under our control plan with incoming inspection applied when parts return.
First articles in 4–7 working days from drawing approval, production in 10–16 working days after FAI sign-off. Anodising adds handling time that is stated in the quote rather than absorbed quietly, and non-stocked alloys add procurement time that we tell you at quote rather than at week three.
Anodising converts the surface of the metal itself into aluminium oxide, so it cannot chip or peel and it adds only 5–75 µm depending on type. Powder coating is a separate polymer layer sprayed on and baked, typically 50–150 µm thick, which gives a wider colour range and covers surface defects but can chip on an edge and hides the metal underneath. Anodising is the choice where dimensions are tight, wear resistance matters, or the machined finish should still read as metal; powder coating is the choice for bold colour, outdoor durability, or on cast alloys such as ADC12 that anodise unevenly.
Yes. Send the certificates with the stock and we inspect it on receipt like any other incoming material. Two things change: we cannot warrant material properties we did not buy, and scrap replacement is handled differently because we do not hold the stock to remake from. For that reason we usually ask for a small quantity allowance on customer-supplied material, and we confirm the arrangement in the quote rather than discovering it after a part is scrapped.
Mecvona signs your NDA — attach it to the RFQ and it comes back executed. Drawings and STEP models stay with the engineering and production team quoting your part, are never used in marketing without written permission, and are not shown to other customers. Where a finish runs on a partner line, that line receives the process requirement and the part, never your model or drawing.
Upload a STEP file and a 2D print. You get back a price, a lead time, the alloy Mecvona would use and why, and whether your tolerance is achievable as machined or needs an anodising allowance built in.
