Physical and mechanical properties of metals and why a fitter must know them.
The choice of metal for a job depends on its properties. Properties are divided into physical and mechanical.
Physical properties
- Colour – copper reddish, brass yellow, steel grey.
- Weight / density – aluminium light, lead heavy.
- Structure – seen on a fractured surface (grains).
- Conductivity – ability to conduct heat and electricity (silver, copper, aluminium are good).
- Magnetic property – iron and steel are attracted by a magnet; copper, aluminium are not.
- Fusibility – ability to melt (tin and lead melt easily).
Mechanical properties
| Property | Meaning | Example |
|---|---|---|
| Ductility | Can be drawn into wire | Copper, mild steel |
| Malleability | Can be hammered or rolled into sheets | Gold, aluminium, lead |
| Hardness | Resists scratching, wear and indentation | Hardened tool steel |
| Brittleness | Breaks without bending | Cast iron, glass |
| Toughness | Withstands shock / impact without breaking | Wrought iron, alloy steel |
| Tenacity (strength) | Resists pulling (tensile) force | Steel |
| Elasticity | Returns to shape after load is removed | Spring steel |
| Plasticity | Keeps the new shape after load is removed | Clay, lead |
Remember Brittleness is the opposite of toughness. A file is hard but brittle – it breaks if dropped.
Quick Revision
- Physical: colour, weight, structure, conductivity, magnetism, fusibility.
- Mechanical: ductility, malleability, hardness, brittleness, toughness, tenacity, elasticity, plasticity.
- Ductile → wire; malleable → sheet.
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