§1Why leave steel
Steel is cheap, stiff and strong, so a nonferrous metal is chosen only when it does something steel cannot — usually being lighter, resisting corrosion, or conducting electricity or heat well.
The four reasons cover most cases: lightness, where aluminium, magnesium and titanium replace steel to save weight; corrosion resistance, where copper alloys and aluminium survive environments that rust steel; conductivity, where copper and aluminium carry current and heat; and bearing and low-friction service, where bronzes run against steel shafts. Each nonferrous family is really a specialist, brought in for the one property that outweighs steel’s cost and stiffness advantage. The rest of the page takes the two most important — aluminium and copper — then the specialty metals.
Contents§2Aluminium and its alloys
Aluminium is about a third the density of steel (2700 against 7850 kg/m³), corrosion-resistant through its own oxide skin, and — in its strong alloys — competitive with steel on strength for weight. Its alloys carry a four-digit code, like steel but with its own key.
| Series | Main alloying element | Character |
|---|---|---|
| 1xxx | pure aluminium | soft, conductive, corrosion-proof |
| 2xxx | copper | high strength, heat-treatable (aircraft) |
| 5xxx | magnesium | marine, weldable, corrosion-resistant |
| 6xxx | magnesium + silicon | general-purpose, extrudable (6061) |
| 7xxx | zinc | highest strength (7075, aerospace) |
| The strongest aluminium, 7075-T6, reaches a specific strength of about 178 kN·m/kg — well above mild steel’s 32 — which is exactly why aircraft are built from it. The letter-and-number temper suffix (the “-T6”) records the heat treatment, since aluminium’s strong alloys are hardened by heat treatment much as steel is. | ||
§3Copper, brass and bronze
Copper leads all common metals for electrical and thermal conductivity and resists corrosion well; its two great alloy families, brass and bronze, add strength and machinability.
Brass is copper alloyed with zinc — the more zinc, the stronger and the more golden, up to about 40 %. The 70/30 “cartridge brass” is the ductile, deep-drawing standard; free-cutting brass adds a little lead to machine superbly, which is why plumbing fittings and turned parts are so often brass. Bronze is traditionally copper alloyed with tin, harder and more wear- and corrosion-resistant than brass, which makes it the classic material for plain bearings, bushes and marine fittings; phosphor bronze and aluminium bronze extend the family. The rule of thumb worth keeping: brass is copper-zinc and machines and forms beautifully, bronze is copper-tin and wears and resists corrosion beautifully.
Contents§4Electrical conductivity
Conductivity is quoted against a fixed benchmark — annealed copper at 100 % on the IACS scale — so any conductor can be read as a percentage of copper.
On the IACS scale, silver is 106 %, copper the reference 100 %, gold 70 %, aluminium 61 %, brass about 28 %, and steel only 10 % (the hero). Aluminium conducts only 61 % as well as copper — yet because it is a third the density, an aluminium conductor of equal resistance is lighter than the copper one, which is why overhead power lines are aluminium while house wiring, where volume not weight is the constraint, is copper. Conductivity read for the constraint that matters — weight or bulk — decides the choice.
§5Light and specialty metals
Beyond aluminium and copper sit metals chosen for extreme cases — the very light, the very strong-for-weight, and the corrosion-proof.
Titanium
Strong as steel at half the weight, and outstandingly corrosion-resistant; costly, so reserved for aerospace, chemical and medical use.
Magnesium
The lightest structural metal (1740 kg/m³); used cast where every gram counts, but flammable as fine chips.
Zinc & lead
Zinc for die-castings and galvanising; lead, dense and soft, for radiation shielding, batteries and weights.
These metals earn their place at the extremes: titanium where strength-for-weight and corrosion together justify the cost, magnesium where nothing else is light enough, zinc and lead for their density, low melting point or chemical behaviour. Each is a specialist answer, not a general-purpose material.
Contents§6Choosing a nonferrous alloy
Selection follows the property that drove you away from steel in the first place.
If the need is lightness with strength, an aluminium or titanium alloy answers, with the aluminium series chosen by whether strength (7xxx), corrosion (5xxx) or extrudability (6xxx) leads. If it is electrical or thermal conduction, copper for volume-limited work and aluminium for weight-limited. If it is a bearing or a corrosion-resistant fitting, a bronze. If it is die-casting or coating, zinc. The chain is: name the property steel lacked, then pick the family built for it, then the grade within it — exactly the property-led method the properties page sets out, now applied across the nonferrous metals.
Contents§7Quick reference
The working core of the page on one card rack.
Leave steel for
weight · corrosion
conductivity · bearings
Aluminium
ρ 2700 · 7075 aerospace
2xxx Cu · 6xxx Mg-Si · 7xxx Zn
Copper alloys
brass = Cu+Zn (form)
bronze = Cu+Sn (wear)
Conductivity
copper 100 % IACS
aluminium 61 %
Specialty
Ti light+strong · Mg lightest