Materials and Material Properties
The Materials and Material Properties domain tests whether you can classify metals, explain properties in plain terms, and justify a material choice for a real workshop job. JCE questions often ask you to match a property to a use, or to explain why mild steel rather than cast iron is chosen for a component.
Classification
Ferrous metals contain iron: mild steel, medium- and high-carbon steel, cast iron. Non-ferrous metals contain no iron: aluminium, copper, zinc, lead, tin. Alloys are mixtures: brass is copper plus zinc, bronze is copper plus tin, and stainless steel is iron with chromium and nickel. Mild steel is the general workshop metal: cheap, weldable, machinable, but it rusts. High-carbon steel takes a hard edge and is used for chisels, files and drills; it is harder but less tough than mild steel.
Properties to know
Strength resists force without breaking; hardness resists scratching and wear; toughness resists shock without cracking; ductility allows drawing into wire; malleability allows hammering into shape; elasticity allows a shape to return; conductivity carries heat or electricity; machinability and weldability describe how easily a metal is cut or joined. Corrosion resistance matters outdoors and in wet rooms.
Worked example
Choose a material for a cold chisel. The cutting edge must resist wear, so high hardness is needed; the body must absorb hammer blows without shattering, so toughness is needed. High-carbon steel is selected, then hardened and tempered: hardened to give a hard edge, tempered to reduce brittleness. Mild steel would be tough, but the edge would burr and dull quickly; cast iron is too brittle for impact.
Traps
Do not confuse hardness with toughness. Do not call aluminium stronger than steel without qualification: it has a better strength-to-weight ratio but lower absolute strength. Remember that rusting applies to ferrous metals, not to all metals.