1.1.22 Ferrous & Non-Ferrous Metals
D&T 2026 — 1.1(c) Product Design Pathway
Comparing the suitability of metals
Choosing a metal means matching its properties to what the product has to do. No metal is best at everything, so a designer weighs up a few questions:
- Function — does it need to be strong, light, conductive, hard-wearing or easy to shape?
- Environment — will it be used outdoors, in water or in contact with food or skin? If so, corrosion resistance matters.
- Aesthetics — what colour, shine and texture does the product need, and should it stay that way?
- Manufacture — can it be cut, bent, welded, cast or machined using the processes available?
- Cost and availability — is it affordable at the scale of production, and available in a suitable stock form?
Ferrous metal — a metal that contains iron. Most ferrous metals are magnetic and will rust unless they are protected.
Non-ferrous metal — a metal that contains no iron. Non-ferrous metals are not magnetic and do not rust, although many tarnish or oxidise.
When explaining suitability, link each property to the product: “Aluminium is suitable for a bicycle frame because its low density keeps the bike light and it resists corrosion when used outdoors.”
Ferrous metals: mild steel, stainless steel and high carbon steel
| Metal | Composition | Aesthetic properties | Functional properties | Typical uses |
|---|---|---|---|---|
| Mild steel | Iron + about 0.15–0.35% carbon | Dull grey; rusts to orange-brown if unprotected | Tough, ductile and malleable; easy to cut, bend, weld and braze; cheap; corrodes easily so needs a finish | Car bodies, bicycle frames, nuts and bolts, furniture frames, girders |
| Stainless steel | Iron + chromium + nickel | Bright, shiny silver; stays clean-looking | Hard and tough; resists rust and staining; hygienic and easy to clean; harder to cut and more expensive than mild steel | Cutlery, kitchen sinks, saucepans, surgical instruments, architectural fittings |
| High carbon steel | Iron + about 0.7–1.4% carbon | Grey | Very hard and keeps a sharp edge, but brittle; can be hardened and tempered | Hand tools such as chisels, screwdrivers, saw blades, springs, drill bits |
Why stainless steel does not rust: the chromium forms a thin, invisible oxide layer on the surface. If the surface is scratched, the layer re-forms, so the steel underneath stays protected.
The effect of carbon: the more carbon steel contains, the harder and stronger it becomes, but the more brittle and less ductile it gets. That is why mild steel bends and high carbon steel snaps.
Non-ferrous metals: titanium, aluminium, copper and brass
| Metal | Aesthetic properties | Functional properties | Typical uses |
|---|---|---|---|
| Titanium | Silver-grey; can be anodised to give blue, gold and purple colours | Very high strength-to-weight ratio; excellent corrosion resistance; biocompatible (safe inside the body); expensive and hard to work | Aircraft parts, medical implants, high-end bicycle frames, watch cases, spectacle frames |
| Aluminium | Light silver; can be polished to a high shine or anodised in colour | Low density (light); good strength-to-weight ratio; corrosion resistant; good conductor of heat and electricity; malleable and easy to recycle | Drinks cans, bicycle and car parts, laptop and phone casings, saucepans, window frames |
| Copper | Warm reddish-orange; tarnishes brown, then turns green (verdigris) outdoors | Excellent conductor of heat and electricity; very ductile and malleable; corrosion resistant | Electrical wiring, water pipes, printed circuit boards, saucepan bases |
| Brass (copper + zinc) | Bright gold colour; polishes well but darkens with age | Harder than copper; casts and machines well; corrosion resistant; low friction | Door handles, hinges, taps, plumbing fittings, musical instruments, electrical pins |
Alloy — a mixture of a metal with one or more other elements, made to improve its properties. Brass and stainless steel are alloys; so are all steels.
Physical properties: melting point, thermal and electrical conductivity
Physical properties describe how a material behaves without being deformed — how it reacts to heat, electricity or its own weight.
Melting point — the temperature at which a solid turns to a liquid.
| Metal | Approximate melting point |
|---|---|
| Titanium | about 1670°C |
| Mild steel | about 1450°C |
| Stainless steel | about 1400–1450°C |
| Copper | about 1085°C |
| Brass | about 900–940°C |
| Aluminium | about 660°C |
Values are approximate and vary with the exact composition. A low melting point makes a metal easier and cheaper to cast, which is why aluminium is widely die-cast. A high melting point suits parts that work in heat, such as engine and jet turbine components.
Thermal conductivity — how well a material lets heat pass through it.
Copper and aluminium are excellent thermal conductors, so they are used for saucepan bases and heat sinks. Stainless steel is a much poorer conductor, so a stainless steel pan often has a copper or aluminium base to spread the heat evenly.
Electrical conductivity — how well a material lets an electric current flow through it.
All metals conduct electricity. Copper is the most widely used conductor because it conducts very well, is ductile enough to draw into wire and is cheaper than silver. Aluminium is used for overhead power cables because it conducts well for its weight.
Mechanical properties: tensile strength, toughness, density, plasticity, malleability, hardness
Mechanical properties describe how a material responds to forces — being pulled, hit, bent or scratched.
| Property | Definition | Example |
|---|---|---|
| Tensile strength | The ability to resist being pulled apart (tension) without breaking | Steel cables in a suspension bridge |
| Toughness | The ability to absorb energy and withstand impact without breaking or cracking | Mild steel car body panels absorb a crash; a hammer head must be tough |
| Density | The mass per unit volume of a material (how heavy it is for its size) | Aluminium (about 2.7 g/cm³) is roughly a third as dense as steel (about 7.8 g/cm³) |
| Plasticity | The ability to be permanently changed in shape without cracking, keeping the new shape once the force is removed | Mild steel being pressed into a car door panel |
| Malleability | The ability to be hammered, pressed or rolled into shape without cracking | Aluminium rolled into foil; copper beaten into bowls |
| Hardness | The ability to resist scratching, wear, cutting and indentation | High carbon steel used for chisel blades |
Strictly, density is a physical property, but the specification groups it with the mechanical properties because it is so important when choosing a metal for a product that must be strong and light.
Strength-to-weight ratio — how strong a material is compared with how heavy it is. Titanium and aluminium have high strength-to-weight ratios, which is why they are used in aircraft and racing bicycles.
Do not confuse hardness and toughness. High carbon steel is very hard (it resists scratching) but it is not tough (it can shatter if dropped). Mild steel is tough but not especially hard.