Aluminium alloy
The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc.
Aluminium alloys are widely used in engineering structures and components where light weight or corrosion resistance is required.
Aluminium alloys can be improperly heat treated, causing internal element separation which corrodes the metal from the inside out.
Selecting the right alloy for a given application entails considerations of its tensile strength, density, ductility, formability, workability, weldability, and corrosion resistance, to name a few.
Pure aluminium is much too soft for such uses, and it does not have the high tensile strength that is needed for building airplanes and helicopters.
Therefore, for a given load, a component or unit made of an aluminium alloy will experience a greater deformation in the elastic regime than a steel part of identical size and shape.
Extrusions are particularly important in this regard, owing to the ease with which aluminium alloys, particularly the Al-Mg-Si series, can be extruded to form complex profiles.
For this reason, bicycle frames made of aluminium alloys make use of larger tube diameters than steel or titanium in order to yield the desired stiffness and strength.
Since aluminium alloys are susceptible to warping at elevated temperatures, the cooling system of such engines is critical.
An important structural limitation of aluminium alloys is their lower fatigue strength compared to steel.
Even a relatively routine workshop procedure involving heating is complicated by the fact that aluminium, unlike steel, will melt without first glowing red.
Thus, the aerospace industry avoids heat altogether by joining parts with rivets of like metal composition, other fasteners, or adhesives.
Yet these parts may still become distorted, so that heat-treating of welded bicycle frames, for instance, can result in a significant fraction becoming misaligned.
[citation needed] Aluminium's intolerance to high temperatures has not precluded its use in rocketry; even for use in constructing combustion chambers where gases can reach 3500 K. The RM-81 Agena upper stage engine used a regeneratively cooled aluminium design for some parts of the nozzle, including the thermally critical throat region; in fact the extremely high thermal conductivity of aluminium prevented the throat from reaching the melting point even under massive heat flux, resulting in a reliable, lightweight component.
Formerly referred to as duralumin, they were once the most common aerospace alloys, but were susceptible to stress corrosion cracking and are increasingly replaced by 7000 series in new designs.
5000 series are alloyed with magnesium, and offer superb corrosion resistance, making them suitable for marine applications.
[55] The main application of metallic scandium by weight is in aluminium–scandium alloys for minor aerospace industry components.
[54] Some items of sports equipment, which rely on high performance materials, have been made with scandium–aluminium alloys, including baseball bats,[56] lacrosse sticks, as well as bicycle[57] frames and components, and tent poles.
U.S. gunmaker Smith & Wesson produces revolvers with frames composed of scandium alloy and cylinders of titanium.
[58] Due to its light-weight and high strength, aluminium alloys are desired materials to be applied in spacecraft, satellites and other components to be deployed in space.
The impact and deposition of solar energetic particles within the microstructure of conventional aluminium alloys can induce the dissolution of most common hardening phases, leading to softening.
The recently introduced crossover aluminium alloys[59][60] are being tested as a surrogate to 6xxx and 7xxx series in environments where energetic particle irradiation is a major concern.
[68] 6063 aluminium alloys are heat treatable with moderately high strength, excellent corrosion resistance and good extrudability.
[72] These alloys were initially developed as a way to increase the usage of cerium, which is over-produced in rare-earth mining operations for more coveted elements such as neodymium and dysprosium,[73] but gained attention for its strength at high temperatures over long periods of time.
[75] Recent work has largely focused on adding higher-order alloying elements to the binary Al-Ce system to improve its mechanical performance at room and elevated temperatures, such as iron, nickel, magnesium, or copper, and work is being done to understand the alloying element interactions further.
