Metals, alloys and protective coatings · Lesson 1 of 4

Metals, alloys and protective coatings: principles and terminology

The three ways sheet metal resists weather, the nine AFS materials and their five families, how to read the codes printed on metal, and why heating coated metal is a hazard.

You will be able to: Name the metals and coatings AFS fabricates, say how each one protects itself or is protected, decode designations such as G90, AZ55, 3003-H14, 16 oz and 316, and state the fume boundary for coated metals.

10 min · 12 slides · 7 questions

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Slide 1 of 12

Three ways sheet metal resists weather

Copper, zinc and aluminum protect themselves: each forms a protective layer on its surface as it weathers.

Sheet steel for building is protected by a metallic coating: zinc for galvanized, a 55% aluminum-zinc alloy for Galvalume.

Anodizing is an oxide coating made on aluminum by passing an electric current through it.

Sources

Copper Brass Bronze Design Handbook: Architectural Applications (A4039) - Copper Development Association
VMZINC Attributes: basic principles of zinc patina - VMZINC
Aluminum: Characteristics, Uses and Problems - U.S. General Services Administration, Historic Preservation
ASTM A653/A653M Standard Specification for Steel Sheet, Zinc-Coated (Galvanized) or Zinc-Iron Alloy-Coated (Galvannealed) by the Hot-Dip Process (public scope only) - ASTM International
ASTM A792/A792M Standard Specification for Steel Sheet, 55 % Aluminum-Zinc Alloy-Coated by the Hot-Dip Process (public scope only) - ASTM International

Glossary

Substrate: The base metal that a coating is applied to, such as the steel under a galvanized or painted sheet.
Galvanized steel: Steel sheet coated with zinc by the hot-dip process, covered by ASTM A653; the zinc gives the steel galvanic and barrier protection.
Galvalume: A trademarked name for steel sheet with a hot-dip 55% aluminum-zinc alloy coating, covered by ASTM A792 and also sold as Zincalume.
Triple-spot test (TST): The average of three coating-weight readings taken across a sheet; a designation such as G90 gives the minimum average.
Temper: The condition of a metal after cold working or heat treatment; for aluminum the letter H marks a strain-hardened temper.
Patina: The stable weathering layer that forms on copper or zinc and protects the metal below it.
PVDF: Polyvinylidene fluoride, a fluoropolymer resin used in long-life factory paint; Kynar 500 is Arkema's PVDF resin and the paint itself is made by a coating maker.
Anodizing: An oxide coating made on aluminum by passing an electric current through it, sold in thickness classes.