A mill test certificate arrives as a single PDF, usually one or two pages, dense with numbers. Most buyers check three things: that the alloy matches, that the tensile figure is above the minimum, and that the certificate exists at all.
That leaves the fields where the actual risk sits untouched. Here is the whole document, in the order it appears, and what to look at in each part.
Start with the header
The top of the page carries four items that decide whether the rest is worth reading.
The standard, with its year. ASTM B209 is not the same document as ASTM B209-14. Standards are revised, tolerances and mechanical minima change, and a certificate that cites no edition cannot be checked against anything. If your purchase order named an edition, the certificate must name the same one.
The alloy and temper, spelled out. 5052-H32, not 5052. Both halves of the designation are what the mechanical values are tied to. A certificate listing only the alloy has no defined strength requirement to test against.
The heat number or cast number. This is the traceability anchor for the whole document. Everything downstream — your incoming inspection, a later failure analysis, a customer's audit — keys off this number. Note it before you do anything else.
The quantity covered. How many pieces, how many kilograms, and which dimensions. A certificate covering 8 tonnes against a delivery of 24 tonnes is not a certificate for your shipment; it is a certificate for a third of it.
Chemical composition: read the limits, not the values
The composition table lists each element with the measured value and, usually, the specification range. The measured value being inside the range is the easy part.
Two rows are where certificates get thin.
"Others, each" and "Others, total." Most alloy specifications cap individual unspecified elements and their sum — commonly 0.05% each and 0.15% total. Certificates that omit these rows are not necessarily fraudulent, but they are incomplete, and incompleteness is exactly what a substitution looks like. If you are buying for a critical application, ask for the full spectro report.
Elements that should be near zero. In 1050 and 1060, copper and manganese are impurities, not additions. A certificate showing 0.04% Cu on 1050 is still in spec but tells you something about the scrap going into that heat. For foil stock and electrical conductor grades, this matters more than the tensile number.
The method matters too. Optical emission spectrometry is the normal production method, and the certificate should say which method was used if the buyer's specification requires it.
Mechanical properties: three places to look
Tensile strength, yield strength and elongation are the three columns most buyers check. The numbers being above the minimum is the least interesting question about them.
Which direction was the test taken? Properties differ between the rolling direction (longitudinal) and across it (transverse). Specifications set minima by direction, and transverse values are usually lower. A certificate reporting only one set of values without stating direction is reporting half the requirement — and it is often the better half.
What gauge length was used for elongation? Elongation is not a material constant; it depends on the test piece. A 50 mm gauge length and a 4D gauge length give different numbers for the same metal, and the acceptance limit is written against one specific basis. Compare your figure to the limit only after confirming both are on the same basis. Getting this wrong in the optimistic direction is how a marginal heat gets accepted.
Is it a measured value or a typical value? This is the single most important distinction on the page. A 3.1 certificate reports actual test results for the heat in question. If the numbers on your certificate are identical to the alloy's published typical values — to the last digit, across every property — you are probably looking at a table copied out of a handbook, not a test.
Dimensions and appearance
Usually a separate small table or a set of check marks. Thickness, width, length, squareness, flatness.
For sheet and plate, the useful check is whether thickness was measured and reported, or only declared as "nominal". Most mill certificates state nominal plus a tolerance band rather than a measured value per piece. That is normal — dimensional verification is your incoming inspection's job, not the certificate's. But if your order specified a tighter-than-standard tolerance, the certificate should show the check.
Three naming systems on one page
The same metal carries different numbers depending on who is writing. A certificate that satisfies a European buyer, an American buyer and a Chinese mill may have to carry all three, and cross-checking them is a real source of error.
For 5052, the four designations in circulation are:
| System | Designation |
|---|---|
| AA / ASTM | 5052 |
| UNS | A95052 |
| EN numeric | EN AW-5052 |
| EN chemical symbol | EN AW-Al Mg2.5 |
The chemical symbol version is the one that trips people up, because it encodes composition rather than a registry number. Al Mg2.5 means roughly 2.5% magnesium — which is 5052. Al Mg3 is 5754. Al Mg4.5Mn0.7 is 5083. They look like a family and they are not interchangeable.
So when a European drawing specifies EN AW-AlMg3 and the certificate comes back with 5754, that is correct and the documents match. When it comes back with 5052, someone has substituted a lower-magnesium alloy that will not meet the corrosion requirement the drawing was written for.
Read the certificate against the designation system used in the order, not against the one you are most familiar with. And if the certificate lists several systems, check that the mapping is right rather than assuming the mill's software got it right — designation cross-references are entered by hand in many mill systems.
The signature block
EN 10204 defines who may issue which certificate type, and the definition is the part buyers skip.
A 3.1 certificate must be issued by the manufacturer's authorized inspection representative, who is required to be independent of the manufacturing department. That is the entire difference between 3.1 and 2.2 — not the presence of numbers, but who signs and what independence they have.
Practically, this means a 3.1 certificate carries the producing mill's name and the signature of a quality function inside that mill. If your document is printed on a trading company's letterhead and describes itself as a 3.1, one of two things is true: it is a copy of the mill's original with the letterhead replaced, or it is mislabelled. Either way it is worth asking for the original scan.
This is not an argument against buying through a trader. It is an argument for knowing which document you are holding. The mill issues the certificate; whoever arranges the shipment passes it along.
Five things that should make you look closer
These are not proof of a problem. They are the patterns that precede one.
- One certificate covering many heats. Legitimate for a small order consolidated from stock, suspicious for a single production lot. Each heat has its own chemistry and its own test.
- Heat number on the certificate does not match the bundle tag. The tag is applied at packing; the certificate is generated at testing. A mismatch breaks the chain, and the chain is the only thing that makes the document useful.
- Test date after the shipment date. Possible with consolidated paperwork, but it should be explained.
- Every value sitting comfortably mid-range. Real heats scatter. Chemistry that lands dead center on eight elements at once is a transcription, not an analysis.
- A scanned photocopy of a photocopy. Ask for the PDF as issued. Modern mill systems produce a clean original with a QR code or verification URL; use it.
How to verify in ten minutes
You do not need a laboratory. You need three comparisons.
Compare the certificate to the order. Alloy, temper, dimensions, quantity, standard edition. Any mismatch is a question, not necessarily an error.
Compare the certificate to the packing. Heat number on the bundle tag against heat number on the page. If the delivery has multiple bundles, confirm the certificate covers all of them.
Compare the values to each other. Yield below tensile, elongation consistent with temper, chemistry summing to roughly 100%. A certificate where the numbers contradict each other internally was assembled, not measured.
For high-value or safety-related orders, add a fourth: ask the mill to confirm the heat number directly. It is a one-line email, and it closes the loop that a PDF cannot close on its own.
What to do when something is missing
Ask, in writing, before the material ships. A missing "others, total" row or an unstated test direction is a two-day fix at the mill and a two-month argument after the container lands.
If the certificate is already the only document you have, our guide to EN 10204 certificate types explains what each class of document is allowed to claim — useful when you are deciding whether what you received is what you paid for.
If you want a certificate checked against the standard before you accept a shipment, send us the PDF and the purchase order line. We will tell you which fields are missing rather than which ones look wrong.