Zinc

2.5-4.5 usd/kg
Circularity potential
Medium
Strength
High
Production energy
High
Stiffness
High
Embodied CO2
Medium
Density
High

Zinc is used mainly as protection for steel (galvanised or electroplated), in brass (copper alloy) and as an industrial additive. A very important metal, it is the forth most consumed, behind iron, aluminium and copper.

Zinc forms a protective oxide (ZnO) layer on its surface when exposed to the atmosphere, which helps protect it from corrosion. While this surface is not usually left bare on products or in automotive applications – zinc is coated or plated to produce a durable and aesthetic surface, such as in kitchen appliances and car body panels – unpainted zinc and zinc-coated steel is suitable for a wide range of industrial and exterior applications.

Zinc coatings are applied to steel by galvanising (HDG), electroplating, painting and spraying (metallising). Hot dip galvanising is by far the most common. Parts are submerged in a bath of molten zinc to produce a uniform coating of zinc and zinc-iron alloy. All types and sizes of parts can be coated in this way. Electroplating is economical, but only for thin layers, and so tends not to be suitable for parts that require a durable and weather-resistant zinc finish.

Steel car bodies are galvanised before being painted. The zinc provides a durable barrier and oxide layer. It provides cathodic protection, which means the zinc will preferentially corrode to protect the underlying steel even if there are small gaps, imperfections, or stone chips.

On its own, or as an alloy, zinc has very good die casting properties, which are utilised in kitchen appliances, tableware, toys and automotive parts. It has excellent fluidity when molten, which means it reproduces surface details and thin wall sections dow to 0.15 mm very well. Complex castings are possible in a single step, which can help reduce fabrications to a single part.

There are two main types of zinc die casting alloy: Zamak and ZA. Zamak alloys contain c. 4% aluminium and provide excellent die casting properties and reasonable strength. The ZA alloys contain higher amounts of aluminium and offer superior strength, hardness and creep resistance. The numbers 8, 12 and 27 represent the approximate weight % of aluminium in each: ZA-8, ZA-12 and ZA-27. In some cases, they offer an economical alternative to steel fabrications, and castings in iron, bronze and aluminium.

These alloys can be electroplated, powder coated, painted and chromate conversion coated. For decorative parts, such as handles and bathroom fitting, electroless nickel is often used. It smooths over holes and imperfections to produce a superior finish. The finished part is plated or coated to look like gold, silver, copper or brass, for example.


Sustainability concerns
Non-renewable ingredients
Raw material generates polluting by-products


ZA-12 (ZA12) is optimised for gravity casting. It demonstrates good pressure tightness for valves, such as for oil, and dimensional stability. An alternative to cast iron, bronze and aluminium, it offers good bearing properties.


Design properties
Cost usd/kg
3.5-4.5
Embodied energy MJ/kg
52.9-72
Carbon footprint kgCO2e/kg
3.5-4.3
Density kg/m3
6000
Tensile modulus GPa
82
Tensile strength MPa
214-400
Compressive strength MPa
227-269
Hardness Mohs
2.5
Brinell hardness HB
89-115
Poissons ratio
0.3
Thermal expansion (µm/m)/ºC
24
Thermal conductivity W/mK
116
Temperature min-max °C
-40 to 100
Thermal
good conductor
Electrical
conductor