Why Mill Certifications Are Non-Negotiable in Aerospace and Defense

What Can Go Wrong Without Mill Certs

The risk of using uncertified material in aerospace and defense is not hypothetical. Without a cert, there is no documented basis for confirming alloy, temper, or chemistry - meaning the material going into a structural part could be the wrong alloy entirely, could be in the wrong temper (affecting strength by 30 to 50 percent), or could have chemistry out of specification. All of these failure modes have occurred in real programs and have led to scrapped parts, fleet inspections, and in-service failures. The cert is the only document that connects the metal in the part to a verified, traceable production lot.

AS9100 Traceability Requirements

AS9100 Revision D, the aerospace quality management standard, requires that organizations control externally provided products and maintain records that demonstrate conformance to requirements. For raw material, this means a documented chain of conformance from the mill to the shop, keyed to a heat or lot number that can be traced back to original chemical and mechanical test data. An AS9100-registered shop that cannot produce mill certs for material in a finished part has a non-conformance in its quality system - an audit finding that may suspend certification until resolved.

NADCAP and First Article Inspection

NADCAP (National Aerospace and Defense Contractors Accreditation Program) auditors review material traceability during process audits. First Article Inspection (FAI) packages, required per AS9102, include a list of all materials used in the part with references to material specifications and traceability documentation. If the FAI reviewer cannot find a mill cert for the aluminum stock used in the part, the FAI is incomplete and cannot be approved. This means no delivery until the cert is found or the part is re-made with certified material.

How Certs Move Through the Supply Chain

When a mill produces a heat of aluminum, it generates the mill cert and ships it with the plate. When a distributor receives the plate and re-sells it in full or cut form, the distributor is responsible for passing the original mill cert (or a certified copy) to the buyer. When the buyer machines the part and delivers it to an OEM or prime contractor, the cert should be in the material traceability package that accompanies the part. The cert must be retained for the life of the program - often 20 to 30 years for defense systems.

What a Complete Cert Package Includes

A complete material certification package for an aerospace aluminum purchase should include the original mill certificate with chemistry actuals, mechanical test results, heat number, alloy and temper, AMS conformance statement, and country of origin. For DFARS-applicable contracts, an explicit DFARS compliance statement is also required. Some programs additionally require a Certificate of Conformance (CoC) from the distributor, which is a separate document in which the distributor certifies that the material they shipped matches the cert on file.

• Mill certificate (MTR) with heat number, chemistry actuals, and mechanical test results
• AMS or ASTM conformance statement from the mill
• Alloy and temper designation
• Country of origin (for DFARS contracts)
• Distributor Certificate of Conformance (if required by program)
• Receiving inspection record confirming heat number match to physical material

What Happens When a Cert Is Found Deficient

If a mill cert is found deficient during receiving inspection, internal audit, or customer review, the affected material must be placed on hold immediately and quarantined from production stock. A Material Review Board (MRB) disposition is typically required: options include return to supplier for replacement, request for supplemental certification from the mill (if the deficiency is documentary rather than substantive), or scrap. If deficient material has already been machined into parts, those parts must be traced and placed on hold pending disposition - a process that can be extremely costly depending on the value-add already applied.

Filing and Retention of Mill Certs

Mill certs should be filed in a searchable system keyed by heat number, purchase order number, and program or job number. Paper filing is common but creates retrieval risk - a cert lost in a filing cabinet cannot be presented in an audit. Digital filing with indexed search by heat number and job number is the more reliable approach. Many aerospace shops scan all incoming certs and attach them to the inventory lot record in their ERP system, creating an automatic link between the physical material and the documentation. Retention requirements vary by contract but 10 to 30 years is typical.

Demanding Certs from Your Supplier

Every aluminum purchase for an aerospace or defense application should be accompanied by a complete mill cert. If your supplier cannot provide one, do not accept the material. A legitimate distributor has mill certs on file for all inventory they received from the mill - if they cannot produce it, either their receiving process failed or the material origin is unverifiable. Requesting certs at the time of order (not at delivery) gives the supplier time to confirm availability and gives you time to review before the material arrives.