AQA GCSE Engineering 8852: materials and their properties (metals and alloys)

spec ref: 3.1.1.1 textbook ref: ch 1.1 pages 2-9

What is strength?

The ability of a material to withstand applied forces without breaking or permanently deforming

What is tensile strength?

The ability to resist pulling forces

What is compressive strength?

The ability to resist pushing forces

What is shear strength?

The ability to resist forces causing layers to slide

What is torsional strength?

The ability to resist twisting forces

What is yield strength?

The stress at which a material begins to deform permanently

What is ultimate tensile strength?

The maximum stress a material can withstand before breaking

What is ductility?

The ability of a material to be stretched without breaking

What is malleability?

The ability of a material to be shaped or compressed without breaking

What is hardness?

The ability to resist wear, scratching and abrasion

What is toughness?

The ability to absorb energy and deform without breaking

What is brittleness?

The tendency to break or shatter without significant deformation

What is stiffness?

The ability to resist bending or deformation (related to Young's Modulus)

What is Young's Modulus?

A measure of stiffness (ratio of stress to strain)

What is a metal?

A material extracted from ore and processed for use

What is an alloy?

A mixture of two or more elements (at least one metal) to improve properties

What is a ferrous metal?

A metal containing iron

What is a non-ferrous metal?

A metal that does not contain iron

What is the effect of increasing carbon in steel?

Increases strength and hardness but decreases ductility and toughness

What is cast iron?

A ferrous alloy containing 3-3.5% carbon

Properties of cast iron

High compressive strength, brittle, poor corrosion resistance, low cost

Behaviour of cast iron

Brittle so may crack under impact, difficult to machine

Uses of cast iron

Engine blocks, vices, machine beds

What is low carbon steel?

Steel containing less than 0.3% carbon

Properties of low carbon steel

Tough, ductile, lower strength, cannot be hardened, low cost

Behaviour of low carbon steel

Easy to form and machine

Uses of low carbon steel

Car bodies, nails, screws, sheet metal

What is high carbon steel?

Steel containing 0.8-1.4% carbon

Properties of high carbon steel

Strong, hard, less ductile, can be hardened

Behaviour of high carbon steel

Difficult to form, more brittle

Uses of high carbon steel

Tools, blades, chisels

What is stainless steel?

Steel containing at least 11.5% chromium

Properties of stainless steel

Strong, hard, corrosion resistant, expensive

Behaviour of stainless steel

Difficult to machine

Uses of stainless steel

Cutlery, sinks, medical equipment

Why do ferrous metals rust?

They react with oxygen and water causing corrosion (rust)

What is aluminium?

A lightweight non-ferrous metal often alloyed

Properties of aluminium

Low density, corrosion resistant due to oxide layer, less strong than steel

Behaviour of aluminium

Easy to shape and machine

Uses of aluminium

Aircraft, drink cans

Why does aluminium resist corrosion?

It forms a thin protective oxide layer that prevents further reaction

What is copper?

A non-ferrous metal with high conductivity

Properties of copper

Excellent electrical conductivity, ductile, corrosion resistant

Behaviour of copper

Easily drawn into wires

Uses of copper

Electrical wiring, pipes

What is brass?

An alloy of copper and zinc

Properties of brass

Corrosion resistant, good machinability, difficult to cast

Uses of brass

Valves, fittings, instruments

What is bronze?

An alloy of copper and tin

Properties of bronze

Hard, corrosion resistant, good for casting

Uses of bronze

Statues, bearings

What is lead?

A dense non-ferrous metal

Properties of lead

Soft, malleable, ductile, corrosion resistant, high density

Uses of lead

Roofing, radiation shielding, weights

What is zinc?

A non-ferrous metal with a low melting point

Properties of zinc

Easy to cast, corrosion resistant

Uses of zinc

Die casting, galvanising

What is corrosion?

A chemical reaction between a material and its environment that damages the material

How does corrosion affect metals?

Reduces thickness, weakens structure and can lead to failure

How can corrosion be prevented?

Painting, plastic coating, galvanising, electroplating, sacrificial protection

What is galvanising?

Coating steel with zinc to prevent corrosion

What is electroplating?

Using electricity to coat a metal with a thin layer of another metal

What is sacrificial protection?

Using a more reactive metal (e.g. zinc) to corrode instead of the main metal

What is cold working?

Deforming metal without heating

Effect of cold working

Increases strength and hardness but reduces ductility (work hardening)

What is work hardening?

The increase in strength and hardness due to cold working

What is annealing?

Heating metal to soften it and increase ductility

What is hardening?

Heat treatment to increase hardness and strength

What is quenching?

Rapid cooling of hot metal to lock in hardness

What is tempering?

Reheating hardened metal to reduce brittleness while keeping some hardness

What is normalising?

Heat treatment that improves toughness and restores ductility

What happens when grain size decreases?

Material becomes harder and stronger but more brittle

What happens when grain size increases?

Material becomes softer and more ductile

Why are alloys used?

To improve properties such as strength, hardness and corrosion resistance

How do hard materials behave during machining?

Difficult to cut and shape

How do ductile materials behave during machining?

Can be shaped without breaking

How do brittle materials behave during machining?

May crack or shatter

How do tough materials behave under impact?

Deform rather than break

What is elasticity?

The ability of a material to return to its original shape after deformation

What is plasticity?

The ability of a material to permanently deform without breaking

What is the difference between a surface finish and a treatment?

A surface finish is a coating applied to protect or improve appearance, while a treatment changes the internal structure and properties of the material

Why do non-ferrous metals not rust?

They do not contain iron so cannot form rust (iron oxide)

Why is bronze better for casting than brass?

Bronze flows more easily when molten, making it more suitable for casting than brass