What is Aluminum?
Aluminum (Aluminium) – a silver-white, soft metal, noted for lightness, high reflectivity, high thermal conductivity, high electrical conductivity, nontoxicity, and corrosion resistance. Aluminum is the most abundant metallic element, comprising 1/12th of the earth’s crust. However, it is never found in nature as an elemental metal but only combined with oxygen and other elements. In ordinary language, aluminum often means aluminum alloy.
Among all kind of metal materials, aluminum wins out either because its properties and performance are superior or because fabrication techniques enable the finished product to be manufactured at a competitive cost. The usage of aluminum continues to increase and expand; new markets such as the automotive sector are beginning to recognize its true unparalleled benefits.
Where and how to get aluminum
Bauxite, a mineral mined from the earth is the major source of aluminum. The bauxite is crushed and sprayed with water, clay and silica removed, and then kiln-dried, and mixed with soda ash and crushed lime. The mixture is then processed in a digester, then reduced under pressure and sent to a settling tank where additional impurities are removed.
After filtering, cooling, and further processing in a precipitator, the mixture is thickened and filtered once more before being heated in a calcinating kiln. The resultant material is alumina, a powdery chemical combination of oxygen and aluminum.
Alumina has to go through smelting and alloying processes to become aluminum of common use. An aluminum smelter contains a cryolite bath (in which the mineral cryolite is melted using electrical current). Alumina, in powder form, is placed into the cryolite bath, where it is melted and separated from its oxygen component, settling beneath the cryolite. The molten aluminum is siphoned from the bottom of the smelter and placed in a crucible, then formed into ingot or transferred to an alloying furnace.
In the alloying furnace, the aluminum ingot is melted, and mixed with alloying metals like Magnesium, silica, copper, etc to form a aluminum alloy which offer a wide range of specific material properties. The physical properties of the alloy are very much determined by the alloy content.
- Manganese offers good corrosion resistance
- Magnesium is good for welding applications
- Copper yields excellent machinability
- Zinc tends to offer very high strength
The molten metal mixture is then cast into solid logs. Logs may be cut to obtain a more manageable billet. Logs and billets are sent to extruders for aluminum extrusion.
Key Characteristics of aluminum
Aluminum when used in sheet, coil or extruded form has a number of advantages over other metals and materials. Where as other materials may offer some of the beneficial characteristics of aluminum, they cannot provide the full range of benefits that aluminum can. Aluminum extruding is a versatile metal-forming process that enables designers, engineers, and manufacturers to take full advantage of a wide array of physical characteristics:
Aluminum has specific gravity of 2.7 and weighs only 0.1 pound per cubic inch. It weighs less by volume than most other metals. In fact, it is about one-third the weight of iron, steel, copper, or brass. Lightweight aluminum is easier to handle, less expensive to ship, and is an attractive material for applications in fields such as aerospace, high-rise construction, and automotive design. When used in the transportation field it can yield significant benefits in a reduction of fuel usage.
Aluminum profiles can be made as strong as needed for most applications. When temperature falls, it becomes even stronger, so it is most commonly used material in cold area
High Strength-to-Weight Ratio:
Aluminum offers a unique combination of lightweight and high strength. Higher strengths can be obtained by adding one or more of the following: manganese, silicon, copper, magnesium, or zinc. Increases can also be accomplished by specialized heat treatments. Nowadays, the aerospace industry and the automotive industry heavily depend on aluminum as the material.
The excellent corrosion resistance of aluminum is due to the presence of a thin, hard protective film of aluminum oxide that bonds tenaciously to the surface. This occurs naturally and can reach a thickness of 0.2 millionths of an inch. Further protection can be done by applying paint or an anodize finish. It does not rust like steel.
Excellent Thermal Conductor:
Aluminum is an excellent conductor of both heat and cold. These factors make aluminum ideal for applications requiring heat exchangers, refrigerator evaporators, and engine components. The aluminum extrusion process is ideal in producing custom shapes that make optimal use of thermal conduction properties.
Excellent Electricity Conductor:
Aluminum is the least expensive metal with an electrical conductivity high enough for use as an electrical conductor. Because of its low density, aluminum will conduct more than twice as much current as the equivalent weight of copper. Various aluminum alloys have different electrical conductivity, and can be adapted for special electrical applications, i.e. power transmission lines.
Because aluminum is non- magnetic it is useful for high-voltage applications, as well as for electronics. It is also used to shield sensitive electronic devices.
Aluminum can be easily formed or reworked into another shape. Aluminum combines strength with flexibility and can flex under loads or spring back from the shock of impact. There are a wide variety of different processes to rework aluminum, the more common ones are: extrusion, rolling, forging, and drawing.
Polished aluminum is an excellent reflector of radiant energy through the entire range of wavelengths. Aluminum’s visible light reflectance (over 80%) has led to its widespread use as lamp reflectors. It can be used to shield products or areas from light, radio waves, or infrared radiation.
Aluminum will not ignite or burn, even when at extremely high temperatures it does not produce toxic fumes.
Suitable to Extreme Cold:
Aluminum is suitable for cryogenic purposes. The strength of aluminum actually increases under very cold temperatures. This has led to the use of it in outer space, as well as for aircraft and for construction in high latitudes.
Aluminum can be recycled at a fraction of the initial production costs. It can be recycled over and over without losing any of its characteristics. This appeals to the manufactures, end uses and environmental consortiums.
Aluminum has an inherent advantage over most other metals because of its attractive appearance and good corrosion resistance. There are many different finishing techniques that can be used. The more common ones are: liquid paint (including acrylics, alkyds, polyesters, and others), powder coatings, anodizing, or electroplating.
Complex shapes can be realized in one-piece extruded aluminum sections without having to effect mechanical joining methods. The resultant profile typically is stronger than a comparable assemblage, less likely to leak or loosen over time. Applications are: baseball bats, refrigeration tubing and heat exchangers. Aluminum parts can be joined by welding, soldering, or brazing, as well as though use of adhesives, clips, bolts, rivets, or other fasteners. Integral joining methods may be especially useful for certain designs. Adhesive bonding is used for such jobs as the joining of aluminum aircraft components.
The tooling or forming parts (dies) are relatively inexpensive and can be made in a short time frame. The various types of tooling utilized can be changed quickly and often during production runs, this makes it cost effective for small production runs.
Historically, aluminum has proven to be one of the most important materials in successful recycling programs. Aluminum offers high scrap value, widespread consumer acceptance, and aluminum recycling enjoys significant industry support.
Aluminum can be recycled and reused over and over without losing any of its characteristics. There is no loss of quality in using recycled aluminum. The recycling of aluminum uses less energy and can offer substantial costs benefits. During many of the manufacturing processes involving aluminum there is scrap generated. This is usually returned to the smelters or casting facilities and reused to make the raw material again. Compared to the initial four pounds of ore to produce one pound of aluminum, every pound of recycled aluminum saves four pounds of ore.