How are metals classified, and how do alloying and treatment change their properties for a product?
Classification of metals into ferrous, non-ferrous and alloys, their common types and stock forms, the properties that distinguish them (strength, ductility, malleability, hardness, conductivity, corrosion resistance), and how alloying, work hardening and heat treatments (annealing, hardening, tempering) are used to change those properties.
A focused answer to the Edexcel 9DT0 content on metals, covering ferrous and non-ferrous metals and alloys, their stock forms and properties, and how alloying, work hardening and heat treatments such as annealing, hardening and tempering modify them for a product.
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this dot point is asking
Edexcel wants you to classify metals as ferrous, non-ferrous or alloys, know common examples, stock forms and properties, and explain how alloying, work hardening and the heat treatments (annealing, hardening, tempering) are used to change a metal's properties to suit a product.
The answer
Ferrous, non-ferrous and alloys
Common metals and uses:
- Mild (low-carbon) steel: cheap, ductile, weldable, magnetic, rusts; car panels, frames, nuts and bolts.
- High-carbon steel: harder, can be heat treated; cutting tools, chisels, springs.
- Stainless steel (steel + chromium + nickel): corrosion resistant; cutlery, sinks, medical tools.
- Aluminium: light, corrosion resistant, good conductor; drink cans, frames, heat sinks.
- Copper: excellent electrical and thermal conductor, ductile; wiring, pipes.
- Brass (copper + zinc): corrosion resistant, machinable, attractive; fittings, instruments.
The properties that distinguish metals
The properties an exam asks you to apply are: strength (resistance to a force), ductility (can be drawn into wire), malleability (can be hammered or pressed into shape), hardness (resistance to scratching and wear), toughness (absorbs impact without fracturing), electrical and thermal conductivity, and corrosion resistance. Density also matters where weight is critical. Stock forms are sheet, plate, bar (round, square, flat), tube, angle, rod and wire in standard sizes.
Changing properties: alloying and work hardening
Changing properties: heat treatment
Heat treatments use controlled heating and cooling to set the structure:
- Annealing: heat then cool slowly. This softens the metal, relieves internal stress from work hardening and restores ductility so it can be worked again.
- Hardening: heat high-carbon steel above its critical temperature then quench (rapid cooling). This makes it very hard but very brittle.
- Tempering: reheat a hardened part to a lower temperature (judged by oxide colour) then cool. This relieves brittleness, trading a little hardness for much more toughness.
Examples in context
Car bodies are pressed from ductile mild steel then coated against rust, while engine blocks are cast in iron for its compressive strength and machinability. Aircraft and bike frames use aluminium alloys for a high strength-to-weight ratio, and aircraft skins and surgical implants use titanium for strength, lightness and corrosion resistance. Hand tools show heat treatment directly: a screwdriver tip or chisel is hardened and tempered so the edge resists wear without shattering, while a length of copper that has work-hardened during bending is annealed to make it ductile enough to bend again.
Try this
Q1. State the difference between a ferrous and a non-ferrous metal. [1 mark]
- Cue. A ferrous metal contains iron as its main element (and usually rusts and is magnetic); a non-ferrous metal contains no iron.
Q2. Explain why work hardening can be a problem when repeatedly bending a metal strip. [2 marks]
- Cue. Cold working makes the metal progressively harder and more brittle, so after enough bends it loses ductility and cracks; annealing restores it.
Q3. Give one property of stainless steel and the alloying element that provides it. [2 marks]
- Cue. Corrosion resistance, provided by adding chromium (which forms a protective oxide layer), making it suitable for cutlery and medical tools.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20184 marksExplain why a low-carbon steel (mild steel) is described as ferrous, and give two properties that make it suitable for a car body panel.Show worked answer →
Award one mark for the meaning of ferrous and up to three for two justified properties.
Ferrous metals are those whose main constituent is iron; mild steel is an alloy of iron with about to carbon, so it is ferrous and (because it contains iron) it is magnetic and will rust unless protected.
Two suitable properties: it is highly malleable and ductile, so it can be pressed and deep-drawn into the curved panel shape without cracking; and it is relatively cheap with good tensile strength and weldability, so panels can be joined and mass produced economically. Markers reward linking each property to the demand of the panel (forming and joining), and many schemes also credit noting it needs a coating because it corrodes.
Edexcel 20226 marksA chisel blade must be hard at the cutting edge but not so brittle that it shatters. Explain how hardening followed by tempering achieves this, referring to the changes in the steel.Show worked answer →
This is an extended-response item marked on levels (correct process knowledge, sequence and a reasoned link to the property required).
Hardening: the high-carbon steel is heated above its upper critical temperature then quenched rapidly in oil or water. The fast cooling traps carbon and produces a very hard but very brittle structure (martensite), so the quenched blade holds an edge but would chip or shatter under impact.
Tempering: the hardened blade is then reheated to a lower temperature (judged by the oxide colour, for example straw to brown for a cutting tool) and cooled. This relieves internal stress and slightly reduces hardness while restoring some toughness, so the edge stays hard enough to cut but the blade resists shattering.
A top answer makes clear the order (harden then temper), names the trade-off (hardness traded for toughness) and links it to the chisel needing a durable but not brittle edge.
Related dot points
- Classification, common types, properties and working characteristics of papers and boards (cartridge, bleed-proof, layout, tracing, grammage by weight) and of timbers (hardwoods, softwoods, manufactured boards such as MDF, plywood and chipboard), including conversion, seasoning, stock forms and the reasons each is selected for a product.
A focused answer to the Edexcel 9DT0 content on papers and boards and on natural and manufactured timbers, covering classification, grammage, common types, seasoning, stock forms and the working properties that decide which is selected for a product.
- Classification of polymers into thermoplastics and thermosetting plastics, their common types, properties and uses, the meaning of recycling codes, and the classification of textiles into natural, synthetic, blended and mixed fibres with their properties and the construction of fabrics by weaving, knitting and bonding.
A focused answer to the Edexcel 9DT0 content on polymers and textiles, covering thermoplastics versus thermosetting plastics, common types and recycling codes, and natural, synthetic and blended fibres with woven, knitted and bonded fabric construction.
- The structure and selection of composite materials (matrix and reinforcement, for example GRP, CFRP, concrete, plywood), the behaviour of smart materials that respond reversibly to a stimulus (shape memory alloys, thermochromic and photochromic pigments, piezoelectric materials, electroluminescent and quantum tunnelling materials), and modern or technical materials developed for new functions (graphene, Kevlar, Gore-Tex, precious metal clay, nanomaterials, technical textiles).
A focused answer to the Edexcel 9DT0 content on composites, smart materials and modern or technical materials, covering matrix-and-reinforcement structure (GRP, CFRP), reversible smart behaviours (shape memory alloys, thermochromics, piezoelectrics) and modern materials such as graphene, Kevlar and Gore-Tex.
- Methods of joining materials (permanent and temporary, including adhesives, welding, brazing and soldering, mechanical fixings such as screws, rivets and knock-down fittings, and stitching) and methods of applying surface finishes and treatments (painting, powder coating, anodising, galvanising, lacquering, polishing, dip coating) and the reasons each is selected for protection, function or aesthetics.
A focused answer to the Edexcel 9DT0 content on joining and finishing, covering permanent and temporary joints (adhesives, welding, fixings, knock-down fittings) and surface finishes and treatments (powder coating, anodising, galvanising) chosen for protection, function or aesthetics.
Sources & how we know this
- Pearson Edexcel A-Level Design and Technology: Product Design (9DT0) specification — Pearson Edexcel (2017)