How to Read an Indian Mill Test Certificate

A mill test certificate (MTC), also called a mill cert or test report, is a document issued by the metal producer that certifies the chemical composition and mechanical properties of a specific heat or lot of material. In theory, every plate and bar you buy should come with one. In practice — especially in the Indian market — they often don't.

This guide walks you through the anatomy of a typical Indian MTC, what each section means, and the red flags that should make you ask for a retest.

What an MTC should contain

At minimum, a credible MTC includes: the producer's name and address, heat number, grade designation, chemical composition (as-tested, not just nominal), mechanical test results (tensile, yield, elongation), dimensions and form, date of test, and the name or stamp of the testing authority.

The heat number problem

The heat number ties the MTC to a specific melt. Without it, the certificate is untraceable — it could belong to any batch the mill ever produced. In the Indian market, heat numbers are frequently omitted on MTCs from smaller distributors. If your MTC doesn't have a heat number, it's a document, not a certificate.

Chemical composition: what to check

Compare the as-tested values against the specification limits. For Al 6061, ASTM B209 requires Mg 0.8–1.2% and Si 0.4–0.8%. If the MTC shows values outside these ranges — or suspiciously round numbers like "Mg: 1.0%, Si: 0.6%" — request an independent verification via PMI or OES.

Mechanical properties: yield vs. tensile

For structural applications, yield strength matters more than tensile. A 6061-T6 plate should show a minimum yield of 240 MPa. If the MTC shows tensile but omits yield, the data is incomplete. If it shows both, verify that the elongation percentage aligns with the temper designation.

Red flags

Watch for: photocopied MTCs with no original stamp, certificates that reference a different dimension than what you received, MTCs showing the exact same values across multiple heats (statistically improbable), and any certificate from a "lab" you cannot independently verify exists.