We depend on it to preserve our food, our medicines and to provide electronic components for our cell phonefs and computers. The main properties that make aluminium a valuable material are its lightweight, strength, recyclability, corrosion resistance, durability, ductility, formability and conductivity.
The Aluminium metal
Aluminium is a relatively new material. It has only been 160 years since the element aluminium was discovered and 100 years or so since a viable production process was established. Other materials, like iron and copper, have been known and used for thousands of years.
Nevertheless, aluminium is today the second-most used metal, after steel. More aluminium is produced each year than all other non-ferrous metals combined.
Aluminium is the third-most abundant element – comprising 8 percent of the earth's crust. The main reason why it was not discovered sooner is that aluminium does not occur naturally in metallic form. Aluminium is found in most rocks, clay, soil and vegetation combined with oxygen and other elements.
Energy
Production of aluminium and aluminium products is dependent upon reasonably priced electricity. In Norway, Hydro produces its own electricity from hydropower facilities for use aluminium production. Elsewhere, Hydro contracts its power needs. Read more about our Energy activities.
Aluminium alloys
Physically, chemically and mechanically, aluminium is a metal like steel, brass, copper, zinc, lead or titanium. It can be melted, cast, formed and machined much like these metals and it conducts electric current.
When combined with small amounts of other chemicals, Aluminium alloys can greatly improve some of aluminiums natural characteristics. Aluminium and its alloys combine a number of features that make it very competitive for a wide range of applications in almost all sectors of industrial activity.
Aluminium properties
The most important properties that make aluminium and its alloys the most economical and attractive for a wide variety of uses are:
- Appearance
- Light weight
- Corrosion resistance
- Physical properties
- Mechanical properties
- Formability
- Recyclability
Light weight
Aluminium has a density of about one-third (2.7g/cm3) that of steel (7.83g/cm3), copper (8.93 g/cm3) and brass (8.53 g/cm3). A one-cubic-meter component of aluminium weighs 2.7 tonnes, while a similar steel component weighs 7.8 tonnes.
Aluminium, with its excellent combination of strength and lightness, is reducing the weight of planes and cars, buses, trucks, trains and boats, and thus decreasing energy consumption and pollution from transportation. Not surprisingly, the use of aluminium in trains, railcars, underground carriages, buses and boats, particularly for bodywork and hulls, is rapidly increasing.
Corrosion resistance
Aluminium resists the progressive oxidization that causes steel to rust. The exposed surface of aluminium combines with oxygen to form an inert aluminium oxide film, which blocks further oxidation. Unlike iron rust, the aluminium oxide film does not flake off to expose a fresh surface to further oxidation. Scratch through aluminium’s protective layer, and it instantly reseals itself. The thin oxide layer itself clings tightly to the metal and is colorless and transparent – invisible to the naked eye.
Physical properties
Aluminium surfaces can be highly reflective. Radiant energy, visible light, radiant heat and electromagnetic waves are efficiently reflected, while anodized and dark anodized surfaces can be reflective or absorbent. This is why aluminium is often selected for a variety of decorative and functional uses, for example, in building facades.
Aluminium displays excellent electrical and thermal conductivity, non-ferromagnetic, non-pyrophoric, non-toxic and has an attractive appearance in its natural finish. Aluminium is unrivalled as a packaging material for food and beverages, as well as pharmaceutical products.
Aluminium foil, even when rolled to just 0.007 mm in thickness, is still completely impermeable and lets neither light, aroma nor taste in or out. Because the metal itself is non-toxic, it releases no aroma or taste substances. Hence, aluminium is unrivalled as a packaging material for food and beverages, as well as pharmaceutical products.
Mechanical properties
Formability is among the more important characteristics of aluminium and many of its alloys. The strength levels of certain aluminium alloys are similar to structural steels. While aluminium has a similar specific modulus of elasticity as steel, the absolute modulus of elasticity is about one-third that of steel. In structural engineering this means higher deformations which can, however, be straightened out by optimized advanced design of the cross section. While such optimization generally allows a weight reduction vs. steel, the optimized cross-section size may be bigger than steel. Unlike steel, many aluminium alloys can be extruded, giving designers a wider range of possible cross-sections.
The machinability of most aluminium alloys is excellent. Aluminium can be joined by a wide variety of methods, including fusion and resistant welding, brazing, soldering, adhesive bonding, and mechanical methods such as riveting and bolting.
Recyclability
Aluminium can be recycled in an endless number of cycles without changing its properties. In addition, aluminium is a valuable metal even as post-consumer scrap. Recent studies have shown that up to 95 percent of the aluminium content of vehicles and 93 percent of the buildings, mainly for the curtain wall, can be recycled. This also lead to business opportunities in the future, as buildings will become “urban mines” for the next generations, enabling a full recycling loop and reducing energy use in production by 95 percent compared to primary aluminium production.
