Aluminum is light at 2.7 g/cm³, melts at a low 660 °C, forms a self-passivating oxide layer that protects it from corrosion, and conducts electricity at 61% of copper’s rate, so a conductor of equal resistance weighs about half as much as copper. Pure aluminum is soft; the strength of scrap depends on the alloy it came from, and the low melting point makes it weak in heat.
Part of Aluminum Smelting
The physical properties that decide where aluminum is used: density, conductivity, corrosion behaviour, workability and melting point.
The Carrier’s Four Properties And What Each Buys
- Light: 2.7 g/cm³, about one-third the density of steel (carrier).
- Corrosion-resistant: its oxide layer forms at once in air and protects the metal beneath; see Aluminum Anodizing for how to thicken it.
- Conductive: 61% of copper’s conductivity at 30% of the weight (carrier).
- Workable: easy to cast, machine, rivet and form (carrier).
The carrier adds that it is “strong”. Pure aluminum is soft, as I recall; the strong aluminum of aircraft and frames is an alloy, and the corpus has no article giving strength numbers for alloys. Any scrap-derived part should be tested by loading a sample before it is trusted in structure.
What The Numbers Give In Practice
Melting point: aluminum melts at 660 °C (Metalworking and Soldering), so it can be melted in an ordinary crucible furnace, which is why scrap recycling is within reach. The same low melting point means it loses strength well below steel’s working temperatures (recalled, unsourced); do not use it in a forge, grate or flue.
Weight for equal conductance: the carrier’s 61% and 30% give, for the same electrical resistance, a cross-section 1 / 0.61 = 1.64 times copper’s and a mass of 1.64 × 0.30 = 0.49 times, so about half. The 30% matches the densities in Copper vs Aluminum, 2.70 against 8.96 g/cm³: 2.70 / 8.96 = 0.30.
What You Need To Use The Properties
- To exploit lightness: designs sized for aluminum’s lower stiffness, not copied from steel.
- To exploit conductivity: larger sections than copper and connections made for aluminum; Copper vs Aluminum explains why joints between the two fail.
- To exploit corrosion resistance: keep it from direct contact with other metals in wet conditions, as I recall contact with copper causes galvanic attack; unsourced.
Common Mistakes
- Specifying aluminum for heat. It softens and melts at a fraction of steel’s temperature.
- Using pure aluminum where strength is needed.
- Expecting a mirror finish to stay. Polished aluminum dulls as its oxide thickens (Polished Sheet Metal).
Safety
Aluminum dust and molten metal
Fine aluminum powder from filing or grinding burns readily, as I recall; keep fines out of fires and furnaces. Molten aluminum and water together cause steam explosions: see Ingot Casting.
What’s Next
- Learn next: Critical Applications - where these properties pay
- Combine with: Why Aluminum Matters - the production verdict