Workshop Science: Materials - Metals, Alloys and Their Properties
Metals, alloys and their properties
This domain tests ferrous and non-ferrous metals, common alloys, mechanical properties and simple material identification. The exam expects candidates to match a service requirement to a suitable material and to distinguish properties such as hardness, toughness, ductility and conductivity.
Core rules
- Ferrous metals contain iron; plain carbon steels are classified by carbon content: low carbon is ductile and weldable, medium carbon is stronger and heat-treatable, high carbon is harder and less tough.
- Cast iron contains much more carbon and is brittle but has good damping and compressive strength.
- Alloying changes properties: stainless steel uses chromium for corrosion resistance; brass is copper-zinc; bronze is copper-tin.
- Aluminium is light, corrosion-resistant and a good conductor; copper has high electrical and thermal conductivity.
- Hardness resists indentation; toughness resists fracture under impact; ductility allows drawing into wire; malleability allows shaping by hammering.
Worked example
A sample has mass 540 g and displaces 200 cm³ of water. Density = 540/200 = 2.7 g/cm³. This matches aluminium, not steel at about 7.85 g/cm³. The reasoning is to use density = mass/volume and compare the result with known material densities; the volume is the displaced volume, not the container volume.
Traps
- Saying cast iron is tough because it is hard; it is actually brittle.
- Confusing brass (Cu-Zn) with bronze (Cu-Sn).
- Assuming all steels have the same carbon content.
- Treating density as weight per piece rather than mass per unit volume.
- Confusing hardness with toughness.