RECYCLING OF ALUMINIUM AND PRODUCTION OF INGOT

The treatment of aluminum scrap to produce new aluminum metal and alloys is an alternative to primary Al production. The chemical composition of the alloys is strictly related to the scrap quality. Therefore, recycled aluminum presents a certain amount of impurities, generally not present in primary alloys, and the alloying elements are more difficult to manage.

Nowadays, this distinction is not completely exhausting. By properly selecting high quality scrap, a purity level close to primary alloys can be achieved in secondary alloys too.

Iron (Fe) plays an important role in distinguishing between primary and secondary Al alloys. This element cannot be easily removed from the molten metal and it forms generally brittle intermetallic compounds that influence the final mechanical properties of the components.

Primary Al alloys present low Fe content and so they are used for applications where the best exploitation of some specific properties is required (mechanical strength, ductility, corrosion resistance, workability, weldability, electrical conductivity); secondary alloys show good castability, which, combined with the natural low volume density of Al alloys, makes them suitable in high-pressure die casting.

Industry and Recycling Trend

The production of secondary aluminium in Europe and United States of America. The contribution of individual European countries is also analyzed. While the production is almost steady in the USA, a continuous growth is evident in Europe, with a production of more than 3 million metric tons in 2014. About half of the total production is concentrated in Germany and Italy. In the considered period, Italy doubled its production from about 500 to 1000 thousand metric tons, becoming the main European producer. Austria, Spain, and Hungary show similar trends with a strong increment in recent years, while France and the Netherlands show an opposite trend. Norway in 2014 recorded a quadruple production increase compared to 1998, but the progress decreases over the next few years until 2014.

Secondary aluminum production from 1998 to 2014 in Europe and some European countries. The production in the USA is also reported. Data elaborated from.

Aluminium properties

Physically, chemically and mechanically, aluminum is a metal similar to steel, brass, copper, zinc, lead or titanium. It can be melted, cast, formed and machined in a similar way to these metals and conducts electric currents. In fact, often the same equipment and fabrication methods are used as for steel.

Light Weight

Aluminum is a very light metal with a specific weight of 2.7 g/cm3, about a third of that of steel. This cuts the costs of manufacturing with aluminum. Again, its use in vehicles reduces dead-weight and energy consumption while increasing load capacity. This also reduces noise and improves comfort levels.

Its strength can be adapted to the application required by modifying the composition of its alloys. Aluminum-magnesium-manganese alloys are an optimum mix of formability with strength, while aluminum-magnesium-silicon alloys are ideal for automobile body sheets, which show good age-hardening when subjected to the bake-on painting process.

Corrosion Resistance

Aluminum naturally generates a protective thin oxide coating which keeps the metal from making further contact with the environment. It is particularly useful for applications where it is exposed to corroding agents, as in kitchen cabinets and in vehicles. In general, aluminum alloys are less corrosion-resistant than pure aluminum, except for marine magnesium-aluminum alloys. Different types of surface treatment such as anodising, painting or lacquering can further improve this property.

Electrical and Thermal Conductivity

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Aluminum is an excellent heat and electricity conductor and in relation to its weight is almost twice as good a conductor as copper. This has made aluminum the first choice for major power transmission lines. It is also a superb heat sink for many applications that require heat to be drained away rapidly, such as in computer motherboards and LED lights.

Reflectivity

Aluminum is a good reflector of visible light as well as heat, and that together with its low weight, makes it an ideal material for reflectors in, for example, light fittings or rescue blankets. Cool roofs made of coated aluminum are invaluable in reducing internal solar heat within a house, by reflecting up to 95% of sunlight.

Ductility

Aluminum is ductile and has a low melting point and density. It can be processed in several ways in a molten condition. Its ductility allows aluminum products to be formed close to the end of the product’s design. Whether sheets, foil, geometrical configurations, tubes, rods or wires, aluminum is up to them all.

Strength at Low Temperatures

In contrast to steel, which rapidly becomes brittle at low temperatures, aluminum shows increased tensile strength as temperatures drop.

Impermeable and Odorless

Aluminum foil is only 0.007 mm in thickness, but is still durable and completely impermeable, keeping any food wrapped in it free of external tastes or smells. It keeps out ultraviolet rays as well.

Moreover, the metal itself is non-toxic and odorless, which makes it ideal for packaging sensitive products such as food or pharmaceuticals. The fact that recycled aluminum can be used reduces the carbon footprint for this stage of food and beverage manufacturers as well.

Non-magnetic

Aluminum is non-magnetic, making it useful for electrical shielding as in computer disks, dish antennas, bus bars or magnet housings.

Non-toxic

Aluminum is non-toxic and is used to make woks, pressure cookers and many other cooking utensils without fear. It is easily cleaned and does not contaminate the food at any stage.