How to Choose an Aluminium Alloy for CNC Machined Parts

1. Define the job before the grade

Begin with the component, rather than the material catalogue. Record the loads it will carry, the surfaces it will contact and the environment in which it will work. A housing, a threaded fitting and a structural bracket may all be aluminium parts, but their priorities can differ.

• Function: which dimensions control assembly, sealing, alignment or movement?
• Environment: will the part be indoors, outdoors, wet, cleaned with chemicals or exposed to another metal?
• Appearance: which faces will be visible, and is a colour or texture match required?
• Purchasing: is this a prototype, a repeat batch or a design that must follow an existing material specification?

Distinguish fixed requirements from preferences. If the drawing already specifies a grade and condition, flag any proposed alternative for approval before a quotation or purchase order treats it as interchangeable.

2. Build a practical alloy shortlist

For a first discussion, 6061, 6082 and 6063 illustrate why material selection is a trade-off. Kaiser describes 6061 tube and pipe as a general-purpose option with useful corrosion resistance and machining characteristics. Hydro positions 6082 extrusions toward structural duty, while 6063 is more appearance-oriented. These are starting points, not component approvals.

References: Kaiser: 6061 tube and pipe technical data; Hydro: 6082 extrusion guidance.

Use the material library and comparison tool to organise candidates. Keep the source and stated condition beside any property value you compare. A value from an extrusion sheet should not silently become a guaranteed value for an unrelated plate or bar specification.

3. Specify temper and starting stock

The same alloy designation can be supplied in different conditions. Kaiser’s 6061 tube and pipe data separates O, T4 and T6 properties; this is a useful reminder to carry the condition into the material description, rather than copying the alloy number alone. That publication is product-specific and should not replace the specification for your ordered stock.

For the purchasing brief, record the alloy, temper, product form, governing standard and any required material records. If one of these is undecided, mark it as open for review. Do not fill a gap with a guessed designation.

Also identify the intended blank: plate, bar, extrusion, forging or casting. Share the blank drawing when one exists. The relationship between the blank and the finished part is part of the manufacturing route, and should be discussed alongside the final geometry.

4. Review geometry and finish together

Machinability depends on more than the grade name. Hydro’s machining guide describes the influence of material condition and chip formation, and recommends assessing machining under conditions that resemble production. For an enquiry, make the difficult features visible instead of assuming that a general machinability description settles the route.

• Mark deep pockets, long bores, thin walls and features accessed from different faces.
• Identify the datums and mating dimensions that need particular attention.
• State whether dimensions apply before or after the specified surface treatment.
• Show masked faces, threads and contact areas where coating is restricted.

Appearance needs its own acceptance reference. Hydro notes that functional anodising of 6082 profiles and a consistent decorative appearance are different requirements. Where visible surfaces matter, discuss the alloy, treatment and an agreed sample together. Review the surface treatment options before fixing the final specification.

The drawing should communicate the required result. The supplier review then establishes the proposed process and any questions that remain before manufacture.

5. Prepare the material review brief

A useful enquiry brings engineering and purchasing information into one place. Send:

• The CAD model and controlled drawing, with part number and revision.
• The required alloy, temper, stock form and material standard, or a clearly marked request for selection support.
• Initial quantity, expected repeat requirement and target delivery date.
• Critical dimensions, surface requirements and the proposed treatment specification.
• Required inspection reports, material documents and receiving acceptance criteria.
• Any approved alternatives, plus the person or process responsible for approving a substitution.

Keep unresolved items explicit. A supplier can ask a focused question about an open requirement; an unstated assumption is harder to identify. Keep agreed decisions with the drawing revision so that repeat orders refer to the same definition.

6. A selection example

Consider a small enclosure with machined holes and a visible anodised face. Start by defining the hole relationships, how the enclosure mounts, which surfaces are visible and what finish reference will be accepted. Then compare candidate stock forms and conditions against those requirements.

If the design instead becomes a bracket carrying a structural load, reopen the material review. The earlier appearance-led choice is not automatically suitable for the new duty. The responsible design team must confirm the mechanical requirement; procurement and manufacturing should work from that approved definition.

This example illustrates the review sequence, rather than prescribing an alloy. The result of a material review is a documented specification and agreed open items, not simply the name of a popular grade.

Sources and scope

This article combines general procurement guidance with the producer references below. The references cover particular products or extrusion contexts. They do not establish CHIHENG stock availability, certified properties or a manufacturing guarantee for your component.

• Kaiser Aluminum — Tube & Pipe Alloy 6061 technical data
• Hydro — 6082 alloy for extruded profiles
• Hydro — A quick guide to the machinability of aluminium alloys