Galvanized steel is a composite material, combining a base metal with a protective coating, which often causes confusion regarding its classification. The core question is whether this common construction material is ferrous or non-ferrous. This article examines the definitions of metal classifications and the specific composition of galvanized steel to provide a clear answer.
Understanding Ferrous and Non-Ferrous Metals
Metals are divided into two major groups based on their chemical composition. The sole determining factor for a metal to be classified as ferrous is the presence of iron (Fe) in its makeup. The term “ferrous” is derived from the Latin word ferrum, the chemical name for iron.
Ferrous metals, such as iron and steel alloys, are prized for their high tensile strength and durability, making them the backbone of construction and heavy industry. A distinguishing characteristic of most ferrous metals is their magnetic nature, which is a direct result of the iron content. However, their iron content also makes them susceptible to rust, which is the oxidation of iron when exposed to oxygen and moisture.
Non-ferrous metals are defined by the absence of iron in their composition. Examples include copper, aluminum, zinc, and brass. These metals are favored in applications requiring corrosion resistance, lighter weight, or specific properties like electrical conductivity. Unlike ferrous metals, they are not magnetic and are more resistant to rust.
The Makeup of Galvanized Steel
Galvanized steel is fundamentally composed of two distinct parts: a steel core and a protective layer of zinc. The base material is steel, which is an alloy of iron and carbon. This combination provides the strength of steel with enhanced corrosion resistance.
The protective layer is applied through a process called galvanization, most commonly hot-dip galvanizing. This method involves immersing the fabricated steel into a bath of molten zinc, typically held at a temperature around 860°F (460°C). This high-temperature immersion causes a metallurgical reaction between the iron in the steel and the molten zinc.
The reaction creates a series of intermetallic zinc-iron alloy layers bonded to the steel substrate, covered by a final layer of pure zinc. This coating functions in two ways: it creates a physical barrier to block oxygen and moisture, and it offers cathodic protection. Cathodic protection allows the zinc to corrode first, protecting the underlying steel even if the coating is scratched or damaged.
Why Galvanized Steel is Classified as Ferrous
Despite the non-ferrous zinc coating, galvanized steel is classified as a ferrous metal. The classification is determined by the composition of the bulk material, or the core, which is steel. Since steel is an iron alloy, its primary component is iron, fitting the definition of a ferrous metal.
The zinc layer is a thin surface treatment intended to enhance the material’s durability, not redefine its fundamental classification. The galvanization process does not alter the underlying steel’s mechanical properties, such as its strength or density. The magnetic properties of the material, a hallmark of ferrous metals, are retained because the massive iron-containing core remains magnetic.
This classification has practical implications, particularly for recycling and separation processes. Because of its magnetic core, scrap galvanized steel can be easily separated from non-ferrous metals using large industrial magnets.