How are metals classified, and how do ferrous metals, non-ferrous metals and alloys differ in properties and use?
Classify metals as ferrous, non-ferrous and alloys, describe their properties and uses, and explain why alloys are made
A focused answer to the O-Level Design and Technology outcome on metals. Ferrous and non-ferrous metals, alloys such as steel and brass, their properties and uses, and why alloys are made.
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What this dot point is asking
SEAB wants you to classify metals into ferrous, non-ferrous and alloys, describe their properties and uses, and explain why alloys are made. You should know that ferrous metals contain iron (and tend to rust), non-ferrous metals do not, and alloys are deliberate mixtures that improve properties. As always, you should be able to recommend a metal for a job and justify it with real properties.
The answer
Ferrous metals
Ferrous metals contain iron. They are usually magnetic and, unless protected, they rust (corrode) when exposed to moisture and air. Common examples:
- Mild steel. An alloy of iron with a small amount of carbon; strong, tough, cheap and easily worked, but rusts. Used widely in construction, car bodies and frames.
- Cast iron. High carbon content; very hard and good in compression but brittle. Used for machine bases, vices and cookware.
Because most ferrous metals rust, they usually need a protective finish such as paint, oil or galvanising.
Non-ferrous metals
Non-ferrous metals contain no iron. They are usually non-magnetic and resist corrosion far better than plain ferrous metals. Common examples:
- Aluminium. Lightweight, corrosion-resistant (it forms a protective oxide layer), and a good conductor. Used for window frames, drink cans, aircraft and outdoor fittings.
- Copper. Excellent conductor of heat and electricity, ductile and corrosion-resistant. Used for wiring, pipes and electronics.
Their corrosion resistance makes non-ferrous metals attractive for outdoor and electrical uses.
Alloys
An alloy is a metal made by mixing two or more elements, at least one a metal, to improve or combine properties. Alloys are made because pure metals often lack what a job needs. Examples:
- Steel (iron plus carbon): much stronger and harder than pure iron.
- Stainless steel (steel plus chromium): resists corrosion, so it does not rust like mild steel. Used for cutlery, sinks and medical tools.
- Brass (copper plus zinc): harder and stronger than copper, easy to machine, attractive. Used for fittings, instruments and decorative items.
Alloying lets engineers tailor strength, hardness, corrosion resistance and workability. Note that steel and stainless steel are ferrous alloys (iron-based), while brass is a non-ferrous alloy.
Choosing a metal for a job
The choice matches properties to the application. An outdoor rail needs corrosion resistance (aluminium or stainless steel). A strong, cheap frame can use mild steel with a protective finish. Electrical wiring needs copper for conductivity. The reasoning, properties matched to the use, is what earns marks.
Examples in context
Example 1. A bicycle frame. A frame must be strong yet light. Aluminium alloy is widely used because it is lightweight, strong enough when shaped into tubes, and corrosion-resistant so it survives weather. Steel frames are stronger and cheaper but heavier and can rust if the finish is scratched. The choice trades weight against cost, each justified by the metal's properties.
Example 2. Electrical wiring in a building. Copper is chosen for wiring because it is an excellent conductor of electricity and is ductile, so it can be drawn into long thin wires without breaking. Aluminium is sometimes used for large cables because it is lighter and cheaper, despite being a poorer conductor. Conductivity, the defining property, drives the material decision.
Try this
Cue. Classify mild steel, aluminium and brass. Answer: mild steel is ferrous, aluminium is non-ferrous, brass is a non-ferrous alloy (copper and zinc).
Cue. Explain why stainless steel does not rust like mild steel. Answer: stainless steel is an alloy of steel with chromium, which makes it corrosion-resistant, whereas mild steel contains no such protection and rusts.
Cue. Give one reason alloys are made instead of using pure metals. Answer: pure metals often lack needed properties (pure iron is soft and weak), so alloying improves strength, hardness or corrosion resistance for the job.
Exam-style practice questions
Practice questions written in the style of SEAB exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Original6 marksA designer is choosing metal for an outdoor handrail. (a) Explain the difference between a ferrous and a non-ferrous metal. (b) Recommend a suitable metal for the handrail and justify your choice with two properties.Show worked answer →
(a) A ferrous metal contains iron and is usually magnetic and prone to rusting (for example mild steel, cast iron). A non-ferrous metal contains no iron, so it does not rust in the same way and is usually non-magnetic (for example aluminium, copper, brass).
(b) Suitable metal: aluminium (or stainless steel). Justification with two properties: aluminium is corrosion-resistant because it forms a protective oxide layer, so it survives outdoors without rusting; and it is lightweight yet strong enough for a handrail, making it easy to install. (Stainless steel would be justified by corrosion resistance from its chromium content and high strength.)
What markers reward: ferrous as iron-containing, magnetic and rust-prone versus non-ferrous as iron-free and corrosion-resistant, and a sensible metal recommendation justified by two real properties linked to outdoor use (corrosion resistance, strength, weight).
Original4 marksExplain what an alloy is and why alloys such as steel and brass are made rather than using pure metals.Show worked answer →
An alloy is a metal made by mixing two or more elements, at least one of which is a metal, to combine or improve their properties. Steel is an alloy of iron and carbon; brass is an alloy of copper and zinc.
Alloys are made because pure metals often lack the properties needed for a job. Pure iron is soft and weak, but adding carbon makes steel much stronger and harder. Pure copper is soft, but adding zinc makes brass harder, stronger and easier to machine. Alloying lets engineers tailor strength, hardness, corrosion resistance and workability to the application, which a single pure metal often cannot provide.
What markers reward: an alloy defined as a mixture of two or more elements (one a metal) with examples, and the reason that alloying improves properties such as strength and hardness beyond what a pure metal offers.
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