Although aluminum is the most abundant metal in the Earth’s crust, it costs more than some less plentiful metals because of the energy needed to extract the metal from ore. When the electrolytic reduction of alumina (Al2O3) dissolved in molten cryolite was independently developed by CharlesHall in Ohio and Paul Heroult in France in 1886, the first internal-combustion-engine-powered vehicles were appearing,and aluminum would play a role as an automotive material of increasing engineering value. Electrification would requireimmense quantities of light-weight conductive metal for long-distance transmission and for construction of the towersneeded to support the overhead network of cables which deliver electrical energy from sites of power generation. Within afew decades the Wright brothers gave birth to an entirely new industry which grew in partnership with the aluminumindustry development of structurally reliable, strong, and fracture-resistant parts for airframes, engines, and ultimately, formissile bodies, fuel cells, and satellite components. There are many wonderful features in using aluminum for many engineering applications.
High Strength-to-Weight Ratio
Aluminum is the lightest metal other thanmagnesium, with a density about one-third that of steel. The strength of aluminum alloys, however, rivals that of mild carbon steel, and can approach 100 ksi(700 MPa). This combination of high strength and light weight makes aluminum especially well suited to transportation vehicles such as ships, rail cars, aircraft,rockets, trucks, and, increasingly, automobiles, as well as portable structures suchas ladders, scaffolding, and gangways.
Ready Fabrication
Aluminum is one of the easiest metals to form and fabricate,including operations such as extruding, bending, roll-forming, drawing,forging, casting, spinning, and machining. In fact, all methods used to formother metals can be used to form aluminum. Aluminum is the metal most suitedto extruding. This process (by which solid metal is pushed through an openingoutlining the shape of the resulting part, like squeezing toothpaste from the tube) is especially useful since it can produce parts with complex cross sections inone operation. Examples include aluminum fenestration products such as windowframes and door thresholds, and mullions and framing members used incurtainwalls, the outside envelope of many buildings.
Corrosion Resistance
The aluminum cap placed at the top of the WashingtonMonument in 1884 is still there today. Aluminum reacts with oxygen very rapidly,but the formation of this tough oxide skin prevents further oxidation of the metal.This thin, hard, colorless oxide film tightly bonds to the aluminum surface andquickly reforms when damaged. High Electrical Conductivity Aluminum conducts twice as much electricityas an equal weight of copper, making it ideal for use in electrical transmissioncables.
High Thermal Conductivity
Aluminum conducts heat three times as wellas iron, benefiting both heating and cooling applications, including automobileradiators, refrigerator evaporator coils, heat exchangers, cooking utensils, andengine components.
High Toughness at Cryogenic Temperatures
Aluminum is not prone to brittlefracture at low temperatures and has a higher strength and toughness at lowtemperatures, making it useful for cryogenic vessels.Reflectivity Aluminum is an excellent reflector of radiant energy; hence its usefor heat and lamp reflectors and in insulation.Nontoxic Because aluminum is nontoxic, it is widely used in the packagingindustry for food and beverages, as well as piping and vessels used in foodprocessing and cooking utensils.
Recyclability
Aluminum is readily recycled; about 30% of U.S. aluminumproduction is from recycled material. Aluminum made from recycled materialrequires only 5% of the energy needed to produce aluminum from bauxite.Often a combination of the properties of aluminum plays a role in its selectionfor a given application. An example is gutters and other rain-carrying goods, made of aluminum because it can be easily roll-formed with portable equipmenton site and it is so resistant to corrosion from exposure to the elements. Another isbeverage cans, which benefit from aluminum’s light weight for shipping purposes,and its recyclability.
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