Can aluminum CNC parts be anodized, and does anodizing change dimensions?

Yes, aluminum parts can be anodized, and anodizing adds a measurable oxide layer to every coated surface, including bore walls and thread flanks. Where a bore or thread must remain within tolerance after finishing, the allowance has to be planned into the machining dimension, and some features need masking. The finish should be stated at quotation rather than after machining.

What material standard applies to 6061 and 7075 aluminum?

The applicable standard depends on the alloy, the temper and the product form, so a single standard number cannot be applied to every purchase. Bar, plate, sheet, tube and forgings of the same alloy can be covered by different specifications. State the required standard and the product form on the drawing or RFQ, and the material is sourced and certified to that requirement.

When should aluminum parts use 5-axis CNC machining?

Five-axis machining is selected for geometry and setup control rather than because the material is aluminum: multi-face parts, compound angles, deep cavities that need angled tool access, undercuts and contoured surfaces where fewer setups reduce accumulated error and handling. Where a part can be held accurately in three or four axes, adding a fifth axis adds cost without adding capability.

What information do I need to request an aluminum CNC quote?

A 3D model, a 2D drawing with the revision, the alloy and temper, the product form if it matters, the applicable material standard, the quantity and expected repeat volume, general and critical tolerances, the surface finish, the inspection and documentation requirements, and the delivery destination.

Aluminum CNC Machining China | 6061 & 7075 Parts

Material Hub · Aluminum CNC Machining

Aluminum CNC Machining in China for Precision Parts

Custom machined aluminum parts from prototypes to repeat production. This page is the starting point for the decisions that come before machining: which alloy and temper, which process, which finish, and how the part will be measured and traced — with 6061-T6 and 7075-T6 covered in depth on their own pages.

If you already know the material and simply need parts made, send the model and drawing; if the alloy is still open, start with the alloy chooser.

Compare 6061 vs 7075 →

Aluminum CNC Capability at a Glance

Milling3, 4 and 5-axis, from plate and billet

TurningCNC turning with live tooling for cross-holes and flats

Core alloys6061-T6 / T651 and 7075-T6, covered in depth

Other grades2024, 7050, 5052, 5083, 6063, MIC6 and others on request

EngineeringDFM and alloy/temper review before quoting

FinishingAnodizing Type II / III, blasting, coating, marking

InspectionCMM, gauges, dimensional report, FAI where required

TraceabilityMill certificate linked to the supplied lot

VolumeOne piece through to repeat production

Quick Answer

Three decisions come before a quotation: which alloy and temper, which process route, and which finish and inspection level. This page is built around the second and third, and it routes you to the first — because alloy selection is a subject in its own right and it is already documented on this site, not something worth restating in a second place.

6061-T6 Choose it when

The part is general-purpose: moderate load, good corrosion behaviour wanted, anodizing is part of the specification, and cost matters.

7075-T6 Choose it when

Strength or weight saving is the driving requirement, and you accept higher stock and machining cost plus more careful finishing.

2024 / 7050 Choose it when

Fatigue performance or a customer specification calls for it — not as a general upgrade over 6061 or 7075.

5052 / 5083 Choose it when

The service environment is aggressive or marine, or the part is formed rather than milled from solid.

6063 Choose it when

The part starts as a profile, or the visible surface and its appearance after anodizing are the deciding factor.

MIC6 Choose it when

The part is a fixture, gauge or tooling plate, where flatness and stability matter more than strength.

Where the rest of the alloy decision lives. Property values, temper designations and machinability bands for 6061, 7075, 2024, 5052, 5083, 6063 and 6082 are set out on the aluminum alloy selection guide. Grade-specific capability, finishes and tolerances are on the 6061-T6 and 7075-T6 pages, and the multi-axis process detail is on the 7075 five-axis page. This page does not repeat them; it covers what happens either side of that choice.

6061 vs 7075: When the Choice Actually Matters

Short answer: for most parts the choice is not close — one of the two is obviously right. It becomes a real decision only when the part sits near a boundary: it carries a load close to what 6061 comfortably handles, or its weight matters enough to pay for 7075.

The question being asked	Points to 6061-T6	Points to 7075-T6
How much load does the part actually carry?	Moderate and predictable, or the part is a bracket, cover or housing	High load in a thin, weight-driven section
Does weight drive the design?	Weight matters, but not enough to change the cost structure	The part is in a weight-sensitive assembly and every gram is argued over
What is the service environment?	Outdoor, humid or mildly corrosive exposure, with protection where needed	Controlled environment, or the part is protected and inspected as part of the programme
How is it joined?	Welded or brazed into an assembly	Bolted, pinned or bonded; welding is not part of the design
Is the finish part of the specification?	Cosmetic anodizing on a visible surface	Function-led finishing, where appearance consistency is less critical
How sensitive is the programme to cost?	Cost is a live constraint, or the volume is high	Performance justifies the higher material and machining cost
How thin are the walls at the tightest tolerance?	Thin sections that have to stay straight through machining	Thin sections stiffened by the higher modulus of the stronger alloy

The full property comparison belongs on the alloy page. Tensile and yield values, density, machinability bands, corrosion and weldability ratings for 6061, 7075 and the other common grades are set out on the aluminum alloy selection guide. What matters here is the decision rule: 7075 is not automatically better than 6061 — the right grade is the one that meets the part’s load, environment and budget rather than the one with the higher number. Where a drawing specifies 7075 on a part that never sees high load, the extra strength is being paid for twice: once in the stock and once in the machining time.

Temper and Dimensional Stability: The Part of the Callout Buyers Miss

Short answer: the alloy is only half the material callout. The temper decides how the stock behaves when you remove material from it — and on pocketed, asymmetric or thin parts it decides whether the part is still in tolerance after it is unclamped.

Designation	What it means at the machine	When it matters most
T6	Solution heat treated and artificially aged to the normal high-strength machining condition	The default for most machined parts, and usually easier to source in the size you need
T651	T6 plus a stretching operation that relieves internal stress in the stock	Thin plate, large pockets and asymmetric material removal, where the part would otherwise move after machining
Overaged tempers (T73, T7351 and similar)	Trade a small amount of strength for improved resistance to stress-corrosion cracking	Where the specification calls for them on a corrosion-sensitive application; sourced against that callout rather than substituted
O / annealed	Soft and formable, with much lower strength	A forming condition, not a machining condition for a structural part — it will not behave like T6
H-tempers (for example H32 on 5052)	Strain hardened to a defined level rather than heat treated	Sheet and formed parts, where formability and corrosion resistance lead the decision

Write the alloy and the temper together, every time. “6061” on a drawing does not tell anyone whether the stock will hold its geometry, and a supplier sourcing to an incomplete callout has no way to know what you meant. The engineering detail on T6 versus T651 — what the stretching step does, and which parts benefit — is on the 6061-T6 page, and where a part is both thin-walled and high-load, the temper decision is part of the same conversation as the alloy.

CNC, Extrusion, Sheet Metal or Casting: Choosing the Route

Short answer: the material being aluminum does not decide the manufacturing route. Geometry, volume and tolerance do — and the wrong route is usually more expensive than any negotiation on the right one.

Situation	Route	Why it wins	What changes if you switch
One to a few hundred complex solid parts	CNC from plate or billet	No tooling commitment, the real alloy in the required temper, and the tightest dimensional control of any route here	The default case: cost sits in setup, programming and cycle time
A long, uniform profile needed repeatedly	Extrusion plus CNC finishing	The cross-section is formed once, so most of the material cost and cycle time disappears from the long dimension	A die and a minimum run; profile tolerance is looser than machining tolerance, so critical surfaces still get machined — see extrusion plus CNC
Flat parts, bends, enclosures, panels	Sheet metal plus CNC	Forming replaces material removal, and sheet is available in corrosion-resistant grades	Material thickness and bend allowance become design constraints; machined bosses and counterbores are added after forming
A complex housing in high volume	Die casting plus machining	Once the tool exists, the near-net shape is produced at a cost machining cannot match	A casting alloy family rather than 6061 or 7075, and draft, porosity and parting-line stock enter the drawing
Rotational parts — shafts, bushings, sleeves	Turning from bar or tube	Round stock is the natural form and the process is efficient on it	Concentricity between features becomes the controlling quality characteristic
Very large, simple plate work	Plate, sawn or profiled, then finish machining	Removal is limited to the features that matter, so material and time are not spent cutting away space	Flatness of the incoming plate and its internal stress become the risk

A route change is an engineering change. Moving a part from solid stock to an extrusion changes the alloy that the part is usually made from, the achievable tolerance on the profile, the surface appearance after anodizing and the minimum order quantity. Those effects belong in the DFM review, where they can be evaluated together, rather than in a purchasing conversation after the drawing is frozen. Process comparisons with casting and additive are covered on the CNC versus die casting and CNC versus 3D printing pages.

Extrusion + CNC: When It Beats Cutting from Solid

Short answer: when the part is long or the profile repeats, forming the shape and machining only the features is usually the largest single cost reduction available — and it is a design decision, not a purchasing one.

The profile carries the shape along its whole length; the machining adds only what the function needs — hole patterns, slots, threaded ends, machined flats and finished end faces. On a long part that is where most of the material and cycle time would otherwise go.

Decision point	Machined from solid	Extrusion plus CNC
Material cost on a long part	Scales with the volume of the stock block, most of which becomes chips	Scales with the cross-section of the profile only — the dominant saving
Tooling	Fixtures and programming only	A die for the profile, plus the fixtures for the machined features
Changing the design	Reprogram and re-fixture	A profile change may require a new die, so changes are more expensive and slower
Tolerance	The machined tolerance applies everywhere	Profile tolerance is looser, so anything critical is machined afterwards rather than assumed from the extrusion
Alloy choice	Free choice of grade and temper	Normally limited to the extrusion alloys, which is a real constraint if the part needs 7075
Appearance after finishing	Even appearance across machined faces	The extrusion surface finish and the machined surfaces can read differently after anodizing
Where it makes sense	Complex geometry, tight interfaces, low to medium volume	Repeating profiles, long parts, and volumes that justify a die and a minimum run

Ask this question early: “which features actually have to be machined, and could the rest of the shape arrive already formed?” On aluminum it is the clearest example of manufacturing engineering paying for itself — but it only works if it is raised before the drawing is frozen, because it changes the alloy, the tolerance map and the finish expectations at the same time.

5-Axis CNC for Complex Aluminum Parts

Short answer: five-axis machining is selected for geometry and setup control, not because the material is aluminum. Where a part can be held accurately in three axes, the extra axis adds cost without adding capability.

Why the extra axes earn their cost	What it changes on the part
Several faces machined in one fixturing	Features across different faces stay related to one datum instead of accumulating setup-to-setup error
Compound angles and contoured surfaces	Surfaces that would otherwise need multiple orientations or a form tool are cut in a single continuous path
Deep cavities needing angled access	A shorter, stiffer tool reaches the feature, which means less deflection and a better floor and wall finish
Undercuts and features behind a wall	Cut without a special tool or a second operation, where the geometry allows
Fewer handling moves on finished surfaces	Reduces the chance of marking or damaging a face that has already been finished

Where it does not pay. Prismatic parts reachable in three axes, simple rotational parts that belong on a lathe, and parts whose accuracy is set by the fixture rather than the tool orientation. The process depth — simultaneous versus indexed machining, datum strategy, thin-wall behaviour and tool access on 7075 — is covered on the five-axis 7075 aluminum page and, at a general level, on CNC machining services.

Milling, Turning and Mill-Turn: Choosing by Part Type

Short answer: the part’s form decides the process, and the deciding factor is usually how many times the part has to be re-held.

Part type	Route	Why
Housings, brackets, plates, manifolds, frames	CNC milling, 3 to 5 axes as the geometry requires	Prismatic features, pockets and hole patterns are what milling does efficiently
Shafts, bushings, sleeves, spacers, collars, pins	CNC turning from bar or tube	Round stock is the natural form, and diameter and concentricity are held in a single setting
A rotational part that also has cross-holes, flats or slots	Mill-turn, or turning with live tooling	Keeping the cross-features in the same setup protects their angular and positional relationship to the turned diameter
A part that would need four or five re-holdings as a prismatic job	Re-evaluate as a mill-turn or five-axis job	Each re-holding is a chance to lose datum continuity, and the handling cost often exceeds the machine-time saving

One setup is worth more than a fast setup. The cheapest process plan is not the one with the shortest cycle on the cheapest machine; it is the one that holds the part the fewest times while still reaching every feature that matters. On aluminum, where a part can be cut quickly, handling and re-datuming are frequently the largest single contribution to error.

What Actually Makes Aluminum Difficult to Machine

Short answer: aluminum is easy to cut and unforgiving to hold. The difficulty is not the material’s hardness — it is thermal movement, thin sections, and the way a part moves when material is removed from stressed stock.

A machined aluminium housing with a very deep rectangular pocket and thin walls standing on a granite surface plate, beside a printed engineering drawing and a dial indicator on a stand — Deep pockets, thin walls and asymmetric material removal are the three features that decide whether an aluminum part stays in tolerance after it leaves the fixture — and all three are visible on the drawing long before a machine is selected.

Challenge	How it shows up	How it is controlled
Thermal movement	Aluminum expands noticeably with cutting heat, so a critical dimension measured on a warm part is not the dimension that ships	Coolant and temperature control, cutting strategies that limit heat input, measurement once the part has stabilised, and in-process probing where the feature is critical
Thin-wall deflection	The wall springs away from the cutter, then relaxes after the clamps are released, so it measures differently in and out of the fixture	Supporting the wall rather than clamping it hard, light finishing passes, and agreeing on the measurement state on the drawing
Residual stress in the stock	Plate and extruded stock carry internal stress that is unbalanced as material is removed, and the part bows or twists	Stress-relieved stock such as T651 where the geometry is asymmetric, roughing separated from finishing, and symmetrical removal where the design allows
Burrs on soft edges	Aluminum forms burrs readily at hole exits and edges, and a burr inside a sealed or sliding volume is a functional defect	A deburring method and an acceptance standard agreed at the DFM stage, not left to the operator
Chip evacuation and re-cutting	Deep pockets trap chips; a chip caught under the cutter marks the finish and damages the edge	Air blast or through-tool coolant, toolpath strategies that clear the pocket, and step-downs that let chips escape
Built-up edge on the tool	Soft or gummy conditions can weld material to the cutting edge, which smears the finish and changes the effective size of the tool	Correct tool geometry and coating, cutting speeds chosen to avoid the built-up-edge range, and sharp edges maintained through a tool-life policy
Tool wear in the stronger alloys	7075 and the higher-strength grades load the tool more heavily, so size drifts and finish deteriorates through a run	A stated tool-life policy with offset management, and replacement before wear reaches the point where the last part differs from the first

The consequence is a shift in where the effort goes. On aluminum, the DFM review is worth more than on most materials: wall thickness, pocket depth, tolerance placement and the choice of temper decide distortion before anyone selects a machine. The general machining requirements these controls come from are set out on CNC machining services, and the grade-specific behaviour is on the 7075-T6 page.

Specifying Alloy, Temper, Form and Standard on a Drawing

Short answer: “aluminum 6061” is not a specification. Four things have to be on the drawing before anyone can buy the material you intended: the alloy, the temper, the product form, and the standard the material is certified against — and the last of those usually depends on the third.

What to state	What it changes in the material you receive
Alloy	Composition and the property band the part is designed against
Temper	Strength and, just as importantly, how the stock behaves when you remove material — see temper and dimensional stability
Product form	Plate, bar, tube, sheet, extrusion or forging. The same alloy in different forms is produced by different processes, carries different internal stress, and can be covered by different specifications. Properties also vary with section thickness.
Applicable standard	What the mill certifies the material to. A standard written for one product form does not automatically cover another, so the standard and the form have to travel together.
Certification requirement	Whether a certificate is needed, in which document type, and naming what — decided now, not reconstructed later
Condition of supply, where relevant	Pre-machined blanks, stress-relieved stock, clad sheet, or material supplied by you

How callouts go wrong, and what it costs

Incomplete callout	What the supplier has to do	The consequence
“Aluminum 6061” with no temper	Source what is available in the size and schedule required	The part may be made from a condition the design never assumed, and the behaviour of the stock differs
Alloy and temper, but no standard	Buy to general commercial availability	The certificate may not satisfy your customer or your own incoming inspection, and a re-order may not match the first
A standard quoted without the product form	Interpret it, or ask	Material sourced to a specification written for a different form, which is the kind of error that is only found at audit
No certificate requirement stated	None	Certificates that were never requested from the mill are difficult and slow to obtain after the fact
Finish not mentioned at quotation	Machine to the nominal drawing	Coating allowance and masking get handled as rework — see finish changes dimensions

The pattern to aim for: alloy + temper + product form + standard + certification requirement, on the drawing or in the RFQ, in that order. Where a customer specification applies, it replaces the generic standard rather than sitting next to it, and the two should not be allowed to contradict each other. Where the standard genuinely is not known yet, say so at quotation — it is a much cheaper conversation then than after the material has been cut.

Choosing a Finish by Requirement, Not by Name

Short answer: finishes are usually specified by name and chosen by requirement. Start from what the surface has to do, and the name follows — along with a clear idea of what it costs and what it changes.

Four identical CNC machined aluminium brackets with different surface finishes in a row: bright as-machined aluminium, matte bead blasted, satin clear anodized and dark charcoal hard anodized — The same bracket, four finishes: as-machined, bead blasted, satin Type II anodized and dark Type III hard anodized. The finish is a functional decision that also changes appearance, dimensional allowance and cost — which is why it belongs on the drawing rather than in the shipping instructions.

The requirement	Finish that usually serves it	What to watch
Protection in handling and storage only	As-machined, with controlled edge condition	The lowest-cost option; tool marks and surface direction remain visible
Uniform matte appearance that hides tool marks	Bead blasting (with or without a following anodize)	Blasting changes the surface texture, which then affects how anodizing reads on it
Corrosion protection with colour, on a visible part	Type II anodizing, clear or dyed	Colour consistency depends on the alloy, the surface preparation and the anodizer; name the appearance requirement, not just “anodized”
Wear resistance where surfaces rub or slide	Type III hard anodizing	The harder film is thicker and darker by nature, and it is less tolerant of tight pre-finish dimensions
Corrosion protection without a decorative oxide, or as a paint base	Chemical conversion coating	Thinner film than anodizing; confirm conductivity requirements if the part is also an electrical path
Colour and a thicker environmental barrier	Powder coating	Builds more thickness than anodizing, so masking and allowances matter more, not less
A reflective or brushed appearance	Polishing or brushing, often before anodizing	Appearance-driven and operator-sensitive; agree a limit sample for visible parts
Part identification that survives service	Laser marking, before or after finishing	Marking sequence changes contrast and readability — agree the sequence with the finish, not after it

Two interactions decide most finish problems. The first is with the alloy: some grades take colour and appearance more consistently than others, and the same finish on two grades will not look identical. The second is with dimensions, which is the next section. Finish options, their typical applications and the anodizing detail for a specific grade are covered on the 6061-T6 page and in general on CNC machining services.

Finish Changes Dimensions

Short answer: anodizing and coating build a layer on the surface, so the dimension you machine is not the dimension you ship. On bores, threads and sealing faces this is a functional problem, not a cosmetic one.

Feature	What the finish does to it	What to agree before machining
Bores and bore walls	The oxide grows into the surface and out of it, so the finished bore is not the machined bore	State that the requirement is the finished dimension; the machining dimension is then set by allowance
Threads	Coating thickens the flanks and can stop a gauge from entering	Mask the thread, tap with an agreed allowance, or specify post-finish gauging — decide which, in writing
Sealing faces and grooves	Flatness and roughness change, and the sealing geometry is sensitive to both	State whether the finish is required on the sealing face at all, and whether it is masked
Mating and locating faces	An assembled fit closes by roughly twice the coating thickness	Identify which faces carry the fit so the allowance is applied where it matters
Datums	A datum surface that has been coated is no longer the surface the part was machined from	Agree whether the datum is measured before or after finishing, and record it on the inspection plan
Marking	Marking before coating and marking after it give different contrast and depth	State the sequence, and confirm readability after finishing

There are only three ways to handle a coating allowance, and all of them need to be chosen before machining: machine the pre-finish dimension so the finished size lands in tolerance; mask the feature so it receives no coating; or measure and accept the coated dimension where the function allows it. Discovering the finish after machining leaves only the third, which is usually the one the drawing did not intend. The full engineering treatment of this, with the anodizing sequence on a real part, is on the 6061-T6 page.

Dimensional Control on Aluminum Parts

Short answer: a tolerance belongs to a feature and a measurement method, not to a part and certainly not to a material. No grade of aluminum holds a tight tolerance by virtue of being aluminum.

Tolerance class	Where it normally applies	How it is verified	What it depends on
Unnoted / drawing default	Non-functional edges, clearance, appearance-only dimensions	General inspection, usually by gauge or caliper	Nothing beyond a normal process
Commonly specified	Mating holes, slots and general interfaces	Calipers, micrometers, gauges or CMM	Stable fixturing and standard setups
Tight	Bores and bearing seats, sealing features, hole-pattern position	CMM, bore gauges, roughness measurement where the finish matters	Part rigidity, tool condition, thermal stability, and the method used to measure it
Qualified-feature level	Only where function genuinely demands it, and only after review	CMM against a defined measurement plan, with the datum scheme reproduced	Feature size and type, stock condition, part rigidity, how the part is held, thermal state during machining, and the measurement method itself

What each GD&T control asks the process to do

True position — hold a feature to a datum reference frame, which is a statement about fixturing and setup strategy as much as about the hole.
Flatness — keep a face from bowing, which on aluminum is a residual-stress and clamping problem before it is a machining problem.
Parallelism and perpendicularity — keep two features related, which is where re-holdings and datum transfer accumulate error.
Concentricity / run-out — keep a turned feature true to a datum axis, which favours holding the part in one setting.
Profile — hold a contoured surface to a tolerance band, which is where multi-axis access and tool stiffness decide the result.

Two rules worth adopting as house standards. First: a tight tolerance applies to qualified features after review, not automatically across a whole part — the achievable value depends on the feature, the stock condition, the rigidity of the part, how it can be held and how it will be measured. Second, and specific to aluminum: because the material moves with temperature, the measurement state is part of the specification — agree whether a thin or flexible feature is measured free or constrained, and at what temperature. Where a dimensional requirement is critical, the honest answer is a capability check on that feature, not a tolerance band quoted for the whole part.

Material Traceability: From Drawing to Certificate to Part

Short answer: traceability is a chain, and it is only as strong as the link nobody thought to record. The chain runs from the callout on the drawing to the certificate for the stock, and from that stock to the parts that were made from it.

Link in the chain	What it establishes
The callout on the drawing	Alloy, temper, product form and standard — the requirement the rest of the chain is judged against
The purchase record for the stock	What was ordered, from whom, and against which specification
The mill certificate	The alloy, temper, lot or heat reference and the properties the material is certified to
Incoming verification	That the material received matches the paperwork — by dimension, marking or verification of the certificate against the order
The link to the production run	Which lot of stock became which batch of parts, on which machine and date
The inspection record	What was measured on those parts, by which method, and the result
Marking on the part or its packaging	The physical key that connects a part in someone’s hand to all of the above

Aluminium plate and round bar stock with cut faces on a bench beside a printed mill certificate sheet that is out of focus, with a finished satin anodized machined part and a digital caliper in the foreground — The certificate is only useful if the lot it names can be connected to the finished part. That connection is the production record, not the paperwork — and it is the part of traceability that fails first when a programme grows.

Decide the certificate requirement at quotation. Where your customer or your own quality system names a certificate type, state it with the order: certificates that were never requested from the mill are slow and sometimes impossible to obtain afterwards, and a chain reconstructed two years later is exactly the situation a certificate is meant to prevent. What a certificate does and does not prove is set out in the inspection section — a mill certificate evidences the stock, not the process.

Inspection and Reports: Deciding What You Receive

Short answer: the document set should be agreed with the drawing, not requested after delivery. Each document answers a different question, and asking for one when you needed another is a common and expensive misunderstanding.

Document	What it demonstrates	What it does not
Dimensional report	Measured values against the drawing limits for the characteristics listed	Nothing about the characteristics that are not on it
Measurement method statement	The instrument and method used for each characteristic, and the temperature or state in which the part was measured	Nothing on its own — but without it the numbers are hard to audit
First-article inspection	Every characteristic documented for a first article, against a named revision	Nothing about the parts made after the first article, unless the process is then controlled
Material certificate	The alloy, temper and lot of the stock supplied	Nothing about how the part was machined, or whether that lot became this part
Coating or finishing record	The finish specification applied, by whom, and against which requirement	Nothing about the dimensional allowance that was or was not made for it
Certificate of conformity	A declaration that the parts conform	It is an assertion, not a measurement — it carries no dimensional evidence

Sampling or 100%? For a general characteristic, sampling against an agreed plan is usually right. For a qualified-feature tolerance on a critical interface, either every part is measured or the process is controlled tightly enough to justify sampling — and which of those applies should be stated rather than assumed.
Which characteristics are on the report? A report that lists the easy dimensions and omits the critical one is the most common gap, and it is invisible unless you compare the report against your own critical list.
Who measures? The instrument, the fixturing of the measurement and the operator technique all move the reported number — see the method statement above.

Agree the report scope with the quotation. The cheapest moment to define what you will receive is when the price is being built, because inspection effort is a real cost. The most expensive moment is after delivery, when the missing measurement is the one that would have told you whether the batch was acceptable.

Aluminum CNC Supplier Qualification Checklist

Aluminum parts fail in predictable places, and almost all of them are visible in the answers to these questions. Ask for the document or the specific answer behind each line rather than a general assurance.

Material and specification

Does the quotation state the alloy and the temper, exactly as on the drawing?
Is the product form — plate, bar, extrusion, sheet or forging — identified and consistent with the standard quoted?
Is the certification requirement stated and available?
Will the supplier confirm material availability before committing to a schedule?
Is there a written process for substitution, and does it require your approval?

Machining

3, 4 or 5-axis milling, turning or mill-turn as the geometry requires — named in the quotation?
A fixture concept with repeatable location, rather than a new setup each time?
A stated process plan for distortion where walls are thin or pockets are deep?
A tool-life policy and offset management, especially on the stronger grades?
In-process probing or an equivalent method where a critical feature would otherwise drift?

Finishing

Which finishes are applied in-house and which are subcontracted, and who controls the subcontractor?
Is the coating allowance or masking handled at quotation, before machining?
Can they confirm readability of marking after finishing?
For visible parts, is there an agreed appearance standard or limit sample?

Inspection and documentation

CMM and the instrument and method named per critical characteristic?
Measurement state and temperature defined for thin or flexible features?
Report scope agreed, including which characteristics appear and at what frequency?
First-article documentation available where the programme requires it?

Supply

Repeat production with a held route, alloy and temper?
Capacity and schedule commitment for the volume you actually expect?
Packaging that protects finished and anodized surfaces in transit?
A second-source or continuity position if the programme needs one?

Prototype to Repeat Production: How the Route Changes

Short answer: the right route at one piece is often not the right route at ten thousand. The transition is worth planning rather than discovering, and it is an engineering project with its own validation — not a purchasing decision taken after the fact.

1–10 pcsPrototype and development

CNC from plate or bar, with a DFM review first. The design is still moving, so tooling commitment is deferred and the objective is a part that validates the design in the real alloy rather than the cheapest possible part.

10–500 pcsPilot and low volume

The same route with a fixture worth keeping and an agreed inspection scope. This is the stage where the design should freeze, and where the coating allowance, the tolerance map and the finish standard get locked in.

500–5,000 pcsRepeat production

Same route, better economics: programming reused, fixture amortised, tool-life policy fixed, records per lot. The route is stable and the value now comes from consistency rather than from further optimisation.

Higher volumeEvaluate a route change

This is where a different process can genuinely win: extrusion plus CNC for long profiles, die casting for complex housings, multi-cavity forming for simple parts. The change brings its own tooling, sample approval and re-validation, and it changes the alloy, the tolerance map and the finish appearance at the same time.

The same part, two different routes

Part	At prototype	At low volume	At high volume
A long ribbed heat sink or rail	Machined from billet — no tooling, full freedom to change the design	Machined from billet, or extrusion plus machining if the profile is settled	Extrusion with only the interfacing features machined; the profile is formed rather than cut
An aluminum housing	CNC from 6061 plate	CNC with an optimised fixture and cycle, still 6061	Evaluate die casting with a casting alloy; the machining scope then reduces to interfaces and sealing faces

Asking for a price at ten times the volume is not the same as asking for the right route at ten times the volume. The first usually returns a lower unit price on the same process. The second can change the process, the alloy and the tolerance map — which is why it belongs in the engineering conversation, and why a route change should be approved and re-validated rather than adopted quietly to hit a cost target. The mechanics of how price actually moves with volume, setup and cycle time are set out on the CNC machining cost page.

Adding a Second Source for an Existing Aluminum Part

Short answer: it is one of the most common reasons buyers approach a new supplier, and it is a different job from a new part. You already have a part that works; the task is to reproduce it without changing anything that matters.

What the new supplier needs	Why it matters
The current released drawing and its revision	A superseded revision is the most expensive mistake available on this job, because the part will pass inspection and still not fit
The alloy, temper, product form and standard exactly as the part is made now	“Equivalent” is where a second source quietly diverges from the first
The finish specification, and ideally a physical sample	Appearance and colour consistency are the hardest characteristics to describe and the easiest to check against a sample
The critical characteristics and how they are verified today	The measurement method has to produce numbers your incoming inspection can compare
The report format your receiving process expects	A report that cannot be matched against your own records is a report that will be re-done
Packaging that is compatible with your line	Finished and anodized surfaces are damaged in handling, not in machining
Any history of deviations on the part and how they were closed	Past problems are the best predictor of what to watch on the first batches

What usually goes wrong

An alloy or temper that is close but not the specified one, sourced because it was available in the required size.
A finish that is nominally the same process but reads differently, discovered on the assembly line rather than at first article.
A datum scheme that is not reproduced, so the measurements look correct while the fit is wrong.
Packaging that protects the part in transit but not the finished surface.
No baseline: the second source is qualified against the drawing alone, with nothing to compare against the part that currently works.

A second source is a copy of a specification, not a copy of a drawing. The drawing carries the geometry; the specification carries the alloy, the temper, the form, the standard, the finish and the acceptance criteria. Where a sample exists, it is the most useful single document in the pack, because it settles the questions that a drawing cannot answer. Two things we hold to on every second-source job: the sample and the drawing are returned or retained only as agreed, and no customer’s drawing or geometry is ever shown to another customer.

What to Send for an Aluminum Quote

The first list is what makes a quotation meaningful. The second is what makes it accurate.

3D model in STEP or native format
2D drawing with the revision you are working to
Alloy
Temper
Product form, where it matters to the standard or the property
Applicable material standard
Quantity, and the repeat or annual volume you expect
General tolerances and the features that need tighter control
Surface finish, and whether any feature needs masking
Inspection and documentation requirements
Delivery destination

The application, and what the part has to do
Mating parts or the assembly it fits into
Whether the finish is functional, cosmetic, or both
Whether this is a second source, with a sample if available
Any history of problems on the part, including where it currently fails
The target date, and what depends on it

Five questions to ask about the quote you receive

Which route has been quoted, and is it the route you would choose if the volume doubled?
Which alloy, temper, product form and standard is the price based on?
Is the coating allowance or masking already accounted for, or will it be discovered after machining?
Which characteristics will appear on the inspection report, measured by which method?
What is the lead time measured from, and what is excluded from the price?

Route Decision Matrix

A starting point for the most common aluminum requirements. It is deliberately a starting point: the DFM review confirms it against your geometry, tolerances and volume.

Project need	Recommended starting route	Why
Prototype bracket, general purpose	6061-T6, CNC from plate	No tooling, the real alloy, and the freedom to change the design after the first article
High-load, weight-critical bracket	7075-T6, 5-axis if the features span several faces	The strength per unit weight is the reason the grade is specified at all
Large, flat, thin plate	Stress-relieved plate with a face-milling and support strategy	Flatness after machining is decided by the stock condition and the fixturing, not by the alloy
Complex multi-face part	5-axis with one datum	Fewer setups means fewer opportunities to lose the relationship between features
Long profile or rail, repeating	Extrusion plus CNC finishing	Most of the material and cycle time is removed from the long dimension
High-volume complex housing	Evaluate die casting with a casting alloy, then machine the interfaces	Once the tool exists, forming the shape beats cutting it away
Cosmetic enclosure	6061 with Type II anodizing	The most consistent appearance across the common grades, with the simplest finish route
Marine or salt-exposed sheet component	5052 or 5083, formed sheet with machined features	Corrosion resistance and formability lead; these grades are made for it
Precision fixture or gauge plate	MIC6 or stress-relieved 6061 plate	Stability and flatness matter more than strength in a tooling application
Rotational part with cross-features	Turning with live tooling, or mill-turn	The cross-features stay related to the turned diameter when both are cut in one setting

Direct Answers

Short, self-contained answers to the questions that come up most often before an aluminum part is quoted.

What is the difference between 6061 and 7075 aluminum?

6061-T6 is the general-purpose machining alloy, with good machinability, corrosion resistance, anodizing response and cost. 7075-T6 is substantially stronger with a better strength-to-weight ratio, and it costs more, welds poorly, resists corrosion less well without protection, and is harder on tooling and on thin walls. The full property comparison is on our alloy selection guide.

Which aluminum alloy is best for CNC machining?

6061-T6 is the best default for general machined parts because it balances machinability, corrosion resistance, strength, finishing response and cost. 7075-T6 is chosen when strength or weight drives the design, 2024 and 7050 where fatigue performance or a specification calls for them, 5052 and 5083 where corrosion or forming leads, 6063 for extrusions and appearance, and MIC6 for tooling where stability matters most.

When should I choose 6061 instead of 7075?

Whenever the part does not genuinely need 7075’s strength. That means moderate and predictable loads, corrosion exposure that matters, welding or brazing in the assembly, cosmetic anodizing, tight cost targets, and high volume. Choosing 7075 on a lightly loaded part pays twice for strength that is never used — once in the stock and again in the machining time.

Is 7075 harder to machine than 6061?

Yes. It loads the tool more heavily, wears tooling faster and is less forgiving on thin walls and deep pockets, which means slower removal rates on some features and a more deliberate tooling strategy. It also has a greater tendency to move on parts where a large proportion of the material is removed.

Does T651 reduce distortion during machining?

T651 stock is stretched after heat treatment to relieve internal stress, so it usually holds geometry better than T6 when material is removed asymmetrically, and on thin plate or large pocketed parts. On a simple symmetrical part machined from bar, T6 is normally adequate and easier to source. The temper belongs in the callout alongside the alloy.

What temper should I specify for an aluminum part?

For most machined structural parts, T6. Where the part is thin, pocketed asymmetrically or has to stay flat after heavy material removal, T651 is the better choice because the stock is stress relieved. Where a specification calls for an overaged temper for corrosion reasons, it is sourced against that callout rather than substituted. The one thing never to do is leave the temper off the drawing.

Which aluminum alloy is best for aerospace parts?

There is no single answer, and any page that gives one is oversimplifying. 7075 is common for high-strength structural parts, 2024 for fatigue-critical structures, and 7050 where the specification requires it. The applicable grade, temper and standard follow the drawing and the customer specification — which is why aerospace work is quoted against the specification rather than against a general recommendation.

Can aluminum parts be anodized, and does it change dimensions?

Yes to both. Anodizing builds an oxide layer on every coated surface, including bore walls and thread flanks, so the machined dimension is not the shipped dimension. Where a bore or thread must remain in tolerance, the allowance has to be planned before machining, and some features need masking. The finish should be stated at quotation rather than after the parts are made.

How do I specify aluminum on a drawing?

State the alloy, the temper, the product form and the applicable standard, plus the certification requirement. The standard depends on the form — a specification written for sheet does not automatically cover plate, bar or a forging — so the standard and the form have to be quoted together. Where a customer specification applies, it replaces the generic standard rather than sitting beside it.

Is CNC machining or extrusion cheaper for aluminum parts?

It depends on the length and the repetition of the profile. For a long part or a repeating cross-section, extrusion plus CNC finishing usually costs less because most of the material is never cut. For a complex part with tight interfaces at low to medium volume, machining from solid wins because there is no die and no minimum run. The two routes also differ in achievable tolerance, alloy choice and appearance after finishing.

When should an aluminum part use 5-axis machining?

When the features span several faces, involve compound angles or contoured surfaces, need angled access into a deep cavity, or would otherwise force three or four separate setups. The axis count is chosen for geometry and setup control, not because the material is aluminum — on a prismatic part that three axes can reach, the fifth axis adds cost without adding capability.

What documents should I request from a supplier?

A dimensional report with the instrument and method named for each characteristic, a material certificate naming alloy, temper and lot, a coating or finishing record, and first-article documentation where the programme requires it. Ask which characteristics appear on the report: a report that omits the critical dimension is the most common gap, and it is invisible unless you compare it against your own critical list.

How much does aluminum CNC machining cost?

There is no universal price, because cost is driven by how much material is removed, the number of setups and fixtures, the tolerances, the finish, the inspection scope and the quantity. On aluminum specifically, a lower grade with a simpler finish often costs less than a higher grade with a tight tolerance on a thin wall — and the difference is a manufacturing decision rather than a materials one. The costing mechanics are set out on our CNC machining cost page.

Aluminum CNC Machining FAQ

Does aluminum grade affect CNC machining cost?

Yes, and not only through the price of the stock. The grade affects machinability and therefore cycle time, tool wear and tooling consumption, the risk of distortion and scrap on thin sections, the finishing route and its consistency, and in some cases availability in the size the part needs. It is why specifying a higher grade than the function requires costs more than the material premium suggests: the extra strength is paid for in the machining hour as well as in the stock.

Does 7075 always cost more than 6061?

7075 generally carries a higher material cost, and depending on geometry and process a higher machining cost, than 6061. We do not publish a fixed multiplier, because the real difference depends on the section and form required, the availability at the time, the geometry, and the quantity — and because published comparisons of the two vary considerably depending on what they include. What can be said usefully is that on a lightly loaded part, 7075 is usually the more expensive answer to a question nobody asked.

What tolerance can aluminum CNC machining hold?

Achievable tolerance depends on the feature, not on the material. Part size, wall thickness, the type of feature, the stock condition and its internal stress, how the part can be held, thermal stability during machining and the method used to measure it all move the result. On aluminum specifically, thermal movement makes the measurement state and temperature part of the specification: a thin or flexible feature can measure differently in the fixture and free on a plate. A tight band is therefore quoted and verified per feature, after review, rather than published as one number for the material.

Why did my aluminum part warp after machining?

Almost always because stress was released rather than introduced. Plate and extruded stock arrive with internal stress from their own forming process; as material is removed, that balance is disturbed and the part moves. It is controlled by using stress-relieved stock such as T651 where the geometry is asymmetric, separating roughing from finishing so the part can settle, removing material symmetrically where the design allows, and supporting thin sections rather than clamping them hard. It is a process-planning outcome, not a machine accuracy issue.

Can you machine aluminum stock that we supply?

Customer-supplied material is workable, with two conditions. First, the material needs to arrive with its identification and certificate intact, because the traceability chain then runs through your paperwork rather than ours — if the alloy, temper or form cannot be evidenced, the part can still be machined but not certified against a specification. Second, supplied stock has to be checked for condition and size before it is committed to a programme, since plate that has been stored badly or sawn to a size that leaves little allowance creates problems that are cheaper to find early.

Is 5052 or 5083 better for marine parts?

Both are chosen for corrosion resistance in marine and salt exposure, and the difference between them shows up in strength, formability and what is available in the thickness you need rather than in a simple ranking. The practical rule is not to treat “marine” as a single requirement: a formed panel, a welded structure and a machined bracket in the same environment will not necessarily land on the same grade, and the decision should combine corrosion behaviour, structure, joining method and the manufacturing process.

What is the difference between T6 and T651?

Both are solution heat treated and artificially aged to a high-strength condition. T651 adds a stretching operation after aging that relieves internal stress in the stock. The visible difference is not in the properties table but in the workshop: T651 moves less when material is removed, so it holds geometry better on thin plates, large pockets and parts where the cuts are not symmetrical. On simple symmetrical parts from bar, T6 is normally sufficient and easier to source in the size required.

Can 7075 be anodized?

Yes, and it is frequently specified with anodizing where the part needs protection. The practical difference from 6061 is appearance: colour and consistency read differently on the higher-copper alloy, and two grades finished in the same tank to the same nominal specification will not necessarily look identical. Where the surface is visible and appearance matters, the grade and the appearance requirement should be specified together, ideally against a sample, rather than asking for “anodized aluminum”.

Does bead blasting affect how anodizing looks?

Yes, and usually more than buyers expect. Blasting changes the surface texture before the oxide forms, so a blasted surface takes colour differently from a machined or polished one and reads as a uniform matte rather than a reflective finish. That is often exactly what is wanted — it hides tool marks and gives consistency across faces — but it has to be specified as a sequence, because blasting after anodizing is a different operation with a different result.

What is the difference between Type II and Type III anodizing?

Type II is the conventional anodic coating used for corrosion protection, colour and appearance across a wide range of aluminum parts. Type III, often called hard anodizing, produces a thicker and harder film for wear resistance where surfaces rub, slide or see abrasive contact. Type III is naturally darker and less decorative, it builds more thickness — which matters more for bores and threads — and it places tighter constraints on the pre-finish dimensions.

What does a material certificate actually prove?

It proves what the stock is: the alloy, the temper, the lot and the properties the mill certified it to. It does not prove that the part in your hand was machined from that lot, that it was machined to the specified condition, or that it meets the drawing. Closing that gap takes the production record linking the lot to the run, plus the inspection result for the characteristics that matter. Certificates and inspection records answer different questions, and buying one while needing the other is a common misunderstanding.

I only know the application, not the alloy. Can you help?

Yes, and it is usually the better starting point. Send the drawing with what the part has to do: the load it carries, the environment it sits in, whether it is welded or bolted, whether weight is being argued over, and what finish it needs. The alloy and temper recommendation follows from those answers, and the DFM review is where it gets confirmed against the geometry. Choosing a grade first and fitting the requirements to it afterwards is where over-specification usually starts.

Do you support both prototypes and repeat production?

Yes, and the route is expected to change between them. Prototype and development parts are machined from plate or bar with a DFM review so the geometry can still move. Once the design settles, the route becomes a repeatable fixture with a held alloy, temper and process route, agreed inspection and per-lot records. Where volume grows far enough to justify it, the alternative routes — extrusion plus CNC, or casting for a complex housing — are worth evaluating as an engineering change rather than adopted quietly to hit a cost target.

How is a drawing revision handled if it changes mid-order?

Work stops against the superseded revision. The change is quantified — which features move, whether the alloy, finish or inspection scope is affected — and approval is obtained before the run continues. Parts already made to the previous revision are identified and dispositioned with you, not mixed into the next delivery. The rule is simple: the revision on the order confirmation is the revision that gets made, and a change is only real once it is written down.

How are anodized parts protected in transit?

Packaging is specified rather than improvised, because a finished aluminum surface is damaged by contact, movement and contamination rather than by machining. The usual controls are separators or moulded dunnage so parts never touch each other, layer pads between layers, containment so parts cannot shift in transit, and protection against moisture where bare or unsealed surfaces are exposed. Where a programme runs regularly, returnable containers with dedicated dunnage are usually the better answer — but they need a pool large enough to cover the round trip and a rule for getting them back.

Do you work with buyers who need a second source?

Frequently, and it is a well-defined job rather than an open one. Send the current revision, the alloy, temper, form and standard as the part is made now, the finish specification with a sample if one exists, the critical characteristics and how they are verified today, and the report format your receiving process expects. The first article is then measured against the sample and the drawing before anything is accepted, and the parts that already work stay the reference point throughout.

Author & technical reviewer

Ming Zhou

Materials & Process Engineer · Xiamen Goldcattle Plastic & Metal Products Co., Ltd.

Aluminum alloy & temper selection
Distortion & thin-wall strategy
Finishing & dimensional allowance
Material traceability

Ming Zhou reviews aluminum parts from the first drawing through to the finishing operation: which alloy and temper the part actually needs, what the drawing leaves unresolved, where the material will move, and what the finish will do to the dimensions it is measured against.

He works with buyers on the questions that arrive after the quotation — why a part warped, why a coated bore no longer accepts its bearing, why an “equivalent” grade is not equivalent, and what a material certificate does and does not establish. He also handles second-source programmes, where the task is to reproduce a part that already works without changing the alloy, the temper or the standard.

Before a quotation is released he checks the material callout for the four things that are most often missing: temper, product form, applicable standard and the certification requirement.

Technical review is by the Goldcattle machining and finishing engineering team. This page is maintained as alloy availability, finishing capability and customer requirements change; updated September 2026.

Send the Drawing

Include the alloy and temper if they are settled, and the application if they are not. The engineering team returns a DFM report covering the material callout, the recommended process route, the finish and its dimensional allowance, the inspection method for each critical feature, and a quotation that states what it is based on.

Upload CAD & Request a Quote →

DFM before quoting · No substitution without written approval · Mill certificates on request

Compare all aluminum alloys →

Scope, claims and how this page is maintained

Purpose: this page covers the decisions around an aluminum machining job — process route, material callout, finish, dimensional control and verification. It is not a price list and not a substitute for a drawing review.
Alloy property data: no tensile, yield, density or machinability values are published on this page. Those values are maintained in one place, on the aluminum alloy selection guide, so that there is a single version of them rather than several that can drift apart.
Tolerances: no single tolerance figure is published for aluminum. A tolerance belongs to a named feature and a stated measurement method, and a tight band applies to qualified features after review rather than across a whole part. Grade-specific capability, with its conditions, is stated on the 6061-T6 and 7075-T6 pages.
Cost: no price, cost ratio or multiplier between grades is published here. Relative cost depends on the section and form required, availability at the time, geometry, quantity and the finishing and inspection scope, so pricing is quoted per project.
Certificates and quality schemes: the documents available and the certification scope are listed on the quality and certifications page. Where a programme requires a specific certificate type or a specific scheme, confirm it against that scope before ordering.
Customer data: no customer drawings, part numbers, names or programme figures appear on this page.
Review: maintained by the Goldcattle engineering team and updated as alloy availability, finishing capability and customer requirements change. Updated September 2026.

Founded in 1998, Xiamen Goldcattle Plastic & Metal Products Co., Ltd. machines metal components and produces molded plastic parts and tooling for international buyers, including aluminum programs. Technical review is by the Goldcattle engineering team. For any order, the governing documents are the drawing, the material specification and the agreed quotation; confirm alloy, temper, product form, standard, tolerance, finish, inspection and documentation requirements for your project before production.