Aluminum Extrusion Specification Checklist for Buyers

Why a Written Specification Matters

An extrusion specification is the contract between the buyer and the extruder. It tells the producer exactly what to make and how to prove it was made correctly. Without it, suppliers may default to their standard stock, which may not fit your drawing.

A weak specification often leads to three common problems. First, the wrong alloy or temper arrives. Second, dimensions are out of tolerance, forcing extra machining or assembly time. Third, surface treatment differs from what the engineering team expected. Each issue costs time, money, and sometimes project delay.

This checklist gives you a structured way to write a complete purchase order. Use it as a template for every extrusion order, from small custom profiles to high-volume production runs.

What Material Details Must Be Included

Start with the material. This is the foundation of the specification. If the alloy and temper are not clearly stated, the extruder cannot guarantee the mechanical properties your design expects.

1. Alloy designation. State the four-digit alloy number, such as 6061 or 6063, or the equivalent standard designation if you are buying from a different region. Do not use only a commercial name like “standard aluminum” or “structural grade.”
2. Temper designation. Specify the temper condition, such as T5, T6, or T651. The temper defines the heat treatment history and therefore the strength and workability of the final profile.
3. Mechanical property limits. State minimum values for yield strength, ultimate tensile strength, and elongation if applicable. Use the applicable standard as your reference.
4. Chemical composition. For high-strength or corrosion-critical applications, specify the allowable ranges for key elements such as silicon, magnesium, copper, and iron.
5. Raw material traceability. Require the extruder to provide heat treatment records and mill test reports that tie the finished product to the specific ingot or billet batch.

Red flags to watch for:

• The supplier quotes a “standard alloy” without naming the number.
• The temper is listed only as “heat treated” without a condition code.
• Mechanical properties are not stated, leaving acceptance to interpretation.
• No reference to a specific standard for composition or testing.

Dimensional and Geometric Tolerances

The second part of the specification is geometry. Extrusion dimensions are not always as precise as machined parts. If your design depends on tight fits or flat mating surfaces, say so.

1. Cross-sectional dimensions. List the critical widths, heights, wall thicknesses, and hole sizes. Indicate which dimensions are critical and which are general.
2. Tolerance class. State the acceptable deviation for each critical dimension. For example, specify a tolerance of plus or minus 0.5 mm for a bearing seat.
3. Straightness. Define the maximum deflection over a given length. A long structural profile can twist or bow during extrusion and cooling.
4. Profile repeatability. If the profile repeats in a long run, specify the maximum dimensional drift between the first and last piece.
5. Corner radius and fillet size. These affect stress distribution and finish quality. State the minimum and maximum values.

Red flags to watch for:

• Tolerances are not specified, so the extruder uses internal defaults.
• Straightness limits are missing for long profiles.
• The drawing shows dimensions but the purchase order does not reference the drawing number and revision.
• No acceptance criteria for out-of-tolerance pieces.

Surface Treatment and Finishing

Surface treatment affects corrosion resistance, appearance, and sometimes mechanical performance. If the profile will be painted, anodized, or left bare, the specification must say what is acceptable.

1. Surface condition. State whether the profile should be bare, brushed, polished, or textured.
2. Anodizing or coating. If applicable, specify the coating type, minimum thickness, and color. For architectural applications, state the architectural anodizing standard or equivalent.
3. Corrosion resistance. For marine, chemical, or outdoor exposure, specify salt spray test requirements or a minimum coating thickness.
4. Protection during shipping. Require the extruder to protect the profile from scratches, handling damage, or contamination during transport.
5. Finish inspection. State how the finish will be checked. For example, specify a visual inspection under a defined light source or a coating thickness gauge method.

Red flags to watch for:

• The purchase order says “anodized” but does not state the finish type or thickness.
• No protection method is specified for delicate profiles.
• Surface treatment is not mentioned at all, so the supplier defaults to a bare extrusion.
• Color or gloss levels are described in vague terms.

Mechanical Testing and Inspection

A specification is only as strong as the way it is verified. The buyer should define how the extruder will prove the product meets the requirements.

1. Visual inspection. State the acceptance criteria for surface defects, dimensional accuracy, and general appearance.
2. Dimensional check. Specify whether the extruder will measure every piece or sample a defined number of profiles from each heat.
3. Mechanical testing. State which tests are required, such as tensile testing, hardness testing, or bending tests. Specify the number of test samples and the method.
4. Chemical analysis. For critical alloys, require a chemical composition certificate from the mill or the extruder.
5. Third-party inspection. For high-value or high-risk projects, require an independent inspection at the extruder’s facility or at the buyer’s site.

Red flags to watch for:

• The supplier offers inspection but does not state the method or sample size.
• Testing is described as “per standard” but the standard is not named.
• There is no provision for retesting after a failed inspection.
• The buyer accepts a verbal assurance instead of a written certificate.

Documentation and Certification

The final part of the specification is the paper trail. If a failure occurs in the field, the buyer needs documents that prove what was delivered and how it was made.

1. Material test certificate. Require a certificate that states the alloy, temper, heat number, and mechanical properties. This should be issued after production, not before.
2. Traceability record. The certificate should include the heat number, the extrusion date, and the production run number. This allows the buyer to trace a problem back to a specific billet.
3. Inspection report. If the extruder performs in-house testing, include a summary report with the results.
4. Nonconformance report. If any material fails, the extruder should provide a report describing the failure, the corrective action, and the disposition of the affected material.
5. Shipping documentation. Include the packing list, material certificates, and inspection reports in the shipment or provide them electronically before delivery.

Red flags to watch for:

• The supplier provides a certificate before the material is produced.
• The heat number is missing or does not match the shipment.
• The inspection report is generic and does not reference the specific order.
• There is no process for handling nonconforming material.

How to Build a Strong Specification

A strong specification is not a list of wishes. It is a set of verifiable requirements. Write each item so that an inspector can check it against a standard or a drawing. Use clear units, specific tolerances, and named standards.

When you are unsure about a requirement, ask the supplier what their standard practice is. Then decide whether that practice meets your needs. If it does not, write the requirement into the purchase order. Do not rely on the supplier to remember what was discussed in a call or email.

A well-written specification reduces disputes. It gives both sides a clear reference point when something goes wrong. It also helps the extruder produce the right product the first time, which saves cost and time for both parties.

Reference Table

Item	Typical Requirement	Why It Matters
Alloy designation	Four-digit number, such as 6061 or 6063	Defines the chemical composition and base properties
Temper designation	T5, T6, T651, etc.	Defines strength and workability after heat treatment
Mechanical properties	Minimum yield, tensile, elongation	Confirms the profile meets engineering load requirements
Dimensional tolerance	Plus or minus value for critical sizes	Ensures fit and function in assembly
Straightness	Maximum deflection over length	Prevents bowing or twisting in long profiles
Surface treatment	Anodizing, bare, coated, with thickness	Affects corrosion resistance and appearance
Material certificate	Heat number, alloy, temper, test results	Provides traceability and proof of compliance

Red Flags That Signal a Problem

Before placing an order, review the quote and the supplier’s response. Several signs suggest the specification may be too weak or the supplier may not understand the requirements.

• The supplier does not ask about tolerances or surface treatment.
• The quote uses a generic material name instead of the specific alloy and temper.
• The supplier offers a lower price for a “similar” alloy without explaining the trade-off.
• The supplier cannot provide a heat number or mill test report.
• The supplier does not state how inspection will be performed.

If you see these signs, ask direct questions. Get the answers in writing. Do not accept a verbal “yes” when the requirement is critical. A written clarification protects both sides and reduces the risk of a rejected shipment.

Final Checklist for the Purchase Order

Use this numbered list as a final pass before sending the purchase order.

1. Alloy number is stated.
2. Temper condition is stated.
3. Mechanical property limits are stated.
4. Chemical composition is stated if required.
5. Critical dimensions and tolerances are listed.
6. Straightness limits are stated.
7. Surface treatment is specified.
8. Inspection method is defined.
9. Material certificate is required.
10. Traceability requirements are stated.
11. Nonconformance process is defined.
12. Drawing number and revision are referenced.

If any item is missing, add it before the order is released. A complete specification is the fastest way to get the right product on the first delivery.