Ferrous and Non-Ferrous Metals
Ferrous vs Non-Ferrous
Metals are divided into two fundamental categories. Ferrous metals contain iron. They are generally strong and magnetic, but rust when exposed to moisture and oxygen unless protected. Non-ferrous metals contain no iron. They resist corrosion naturally and are non-magnetic—making them valuable in electrical applications (where magnetic interference must be avoided) and in marine environments. The third category, alloys, are mixtures of two or more metals (or a metal and another element) engineered to achieve properties neither constituent has alone.
Ferrous metals contain iron and tend to rust; non-ferrous metals do not contain iron and resist corrosion naturally. Mild steel (ferrous) and aluminium (non-ferrous) are the most commonly used metals in manufacturing industry.
Ferrous Metals — Named Examples
Cast iron contains 2–4% carbon, making it very hard and brittle. It cannot be bent or forged—it fractures rather than deforming. Used for machine tool beds, drain covers and engine blocks, where rigidity under compression is needed and brittleness is acceptable. It has excellent compressive strength but low tensile strength.
Mild steel (also called low-carbon steel) contains 0.1–0.3% carbon. It is the most widely used engineering material in the world. Tensile strength is approximately 400–500 MPa. It is ductile, malleable and weldable—but rusts readily and must be painted, galvanised or powder-coated for outdoor use. Used in structural beams, car bodies, pipework and general fabrication.
Medium and high carbon steels have progressively more carbon (0.3–1.4%), giving greater hardness and wear resistance but reduced ductility and weldability. High carbon steel is used for cutting tools, springs and high-stress components. It can be heat-treated (hardened and tempered) to control the balance of hardness and toughness.
Non-Ferrous Metals — Named Examples
Aluminium has a density of approximately 2.7 g/cm3—about one third the density of steel. It naturally forms an oxide layer that prevents further corrosion. Good conductor of heat and electricity. Used in aircraft frames, food cans, window frames and heat exchangers. Can be anodised to enhance its oxide layer and add colour. Recycling aluminium uses only around 5% of the energy needed to smelt virgin aluminium from bauxite.
Copper is an excellent electrical conductor (second only to silver) and has high thermal conductivity. It is ductile enough to be drawn into fine wire and malleable enough to be beaten into shape. Used in electrical wiring, plumbing pipes and heat exchangers. Copper weathers to a green patina (copper carbonate) that actually protects the underlying metal.
Common Alloys
Alloys are engineered mixtures. The specification names brass and bronze specifically:
- Brass—copper (roughly 65%) and zinc (roughly 35%). Harder than copper alone, non-sparking, and corrosion-resistant. Used in musical instruments, plumbing fittings, electrical connectors and decorative hardware. Machines cleanly with a good surface finish.
- Bronze—copper and tin (historically around 88% copper, 12% tin). Harder and more corrosion-resistant than copper alone. Used in bearings, marine propellers, bells and sculpture. The tin content makes it harder to machine than brass but gives superior strength for load-bearing applications.
Brass = copper + zinc. Bronze = copper + tin. Both are corrosion-resistant alloys derived from copper. Brass is commonly used for plumbing fittings and musical instruments; bronze for marine propellers and bearings.
Working Properties
Designers and engineers select metals based on specific working properties. These are the key terms the exam tests:
| Property | Definition | High-value example |
|---|---|---|
| Tensile strength | Resist pulling forces | Mild steel (~400–500 MPa) |
| Hardness | Resist surface indentation or scratching | High carbon steel |
| Ductility | Drawn into wire | Copper, aluminium |
| Malleability | Beaten or pressed into shape without cracking | Aluminium, copper |
| Toughness | Absorb impact energy without fracturing | Mild steel |
| Elasticity | Return to original shape after load removed | Spring steel |
Metals are supplied in standard stock forms to minimise waste when cutting components to size. Common forms include:
- Sheet—flat rolled metal, typically 0.5–3 mm thick for mild steel and aluminium. Used for pressed body panels, enclosures and cans.
- Bar (flat/square)—solid rectangular or square cross-section. Used for structural brackets, levers and frames.
- Rod (round bar)—solid circular cross-section, turned in a lathe to produce shafts and pins.
- Tube—hollow circular section. High strength-to-weight ratio because material is placed at maximum distance from the neutral axis. Used for cycle frames, scaffold poles and handrails.
- Angle—L-shaped cross-section. Provides stiffness to a structure when welded or bolted at corners. Used in frames, brackets and shelving.
Ferrous metals must be protected from moisture and oxygen to prevent rust. Common methods include:
- Galvanising—dipping steel in molten zinc. The zinc acts as a sacrificial coating: it corrodes preferentially, protecting the steel beneath. Used for outdoor structures, car body panels undercoating and corrugated roofing.
- Powder coating—electrostatically applying a dry polymer powder to a metal surface, then curing it in an oven. Produces a hard, even coating in a wide range of colours. More durable than conventional liquid paint and produces less VOC waste.
- Painting—the simplest surface treatment. Requires proper surface preparation (degreasing, priming) to adhere well. Relatively low cost but needs re-application as the paint chips or weathers.
- Anodising (aluminium)—an electrochemical process that thickens the natural oxide layer on aluminium. The thickened layer is then dyed. Produces a decorative and very wear-resistant surface. Used on window frames, bicycle components and consumer electronics.