Aluminium alloy

 ( Alloys ) 

An aluminium alloy (British English/IUPAC) or aluminum alloy (NA; see spelling differences) is an alloy in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin, nickel and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories Heat treating and non-heat-treatable. About 85% of aluminium is used for wrought products, for example rolled plate, foils and . Cast aluminium alloys yield cost-effective products due to their low melting points, although they generally have lower tensile strengths than wrought alloys. The most important cast aluminium alloy system is Silumin, where the high levels of silicon (4–13%) contribute to give good casting characteristics. Aluminium alloys are widely used in engineering structures and components where light weight or corrosion resistance is required.I. J. Polmear, Light Alloys, Arnold, 1995

Alloys composed mostly of aluminium have been very important in aerospace manufacturing since the introduction of metal-skinned aircraft. Aluminium–magnesium alloys are both lighter than other aluminium alloys and much less flammable than other alloys that contain a very high percentage of magnesium.

Aluminium alloy surfaces will develop a white, protective layer of aluminium oxide when left unprotected by anodizing or correct painting procedures. In a wet environment, galvanic corrosion can occur when an aluminium alloy is placed in electrical contact with other metals with more positive corrosion potentials than aluminium, and an electrolyte is present that allows ion exchange. Also referred to as dissimilar-metal corrosion, this process can occur as exfoliation or as intergranular corrosion. Aluminium alloys can be improperly heat treated, causing internal element separation which corrodes the metal from the inside out.

Aluminium alloy compositions are registered with The Aluminum Association. Many organizations publish more specific standards for the manufacture of aluminium alloys, including the SAE International standards organization, specifically its aerospace standards subgroups, SAE aluminium specifications list, accessed 8 October 2006. Also SAE Aerospace Council , accessed 8 October 2006. and ASTM International.

In general, stiffer and lighter designs can be achieved with aluminium alloys than is feasible with steels. For instance, consider the bending of a thin-walled tube: the second moment of area is inversely related to the stress in the tube wall; that is, stresses are lower for larger values. The second moment of area is proportional to the cube of the radius times the wall thickness, so increasing the radius (and weight) by 26% will lead to a halving of the wall stress. 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. In automotive engineering, cars made of aluminium alloys employ made of extruded profiles to ensure rigidity. This represents a radical change from the common approach for current steel car design, which depend on the body shells for stiffness, known as unibody design.

Aluminium alloys are widely used in automotive engines, particularly in and due to the weight savings that are possible. Since aluminium alloys are susceptible to warping at elevated temperatures, the cooling system of such an engine is critical. Manufacturing techniques and metallurgical advancements have also been instrumental for successful applications in automotive engines. In the 1960s, the aluminium of the Chevrolet Corvair earned a reputation for failure and stripping of screw thread, which is not seen in current aluminium cylinder heads.

An important structural limitation of aluminium alloys is their lower fatigue strength compared to steel. In controlled laboratory conditions, steels display a fatigue limit, which is the stress amplitude below which no failures occur – the metal does not continue to weaken with extended stress cycles. Aluminium alloys do not have this lower fatigue limit and will continue to weaken with continued stress cycles. Aluminium alloys are therefore sparsely used in parts that require high fatigue strength in the high-cycle regime (more than 10⁷ stress cycles).

Aluminium is subject to internal stresses and strains. Sometimes years later, improperly welded aluminium bicycle frames may gradually twist out of alignment from the stresses of the welding process. Thus, the aerospace industry avoids heat altogether by joining parts with rivets of like-metal composition, other fasteners, or adhesives.

Stresses in overheated aluminium can be relieved by heat-treating the part in an oven and gradually cooling it—in effect annealing the stresses. 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. If the misalignment is not too severe, the cooled parts may be bent into alignment. If the frame is properly designed for rigidity (see above), that bending will require enormous force.

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.

• The greater coefficient of thermal expansion of aluminium causes the wire to expand and contract relative to the dissimilar-metal screw connection, eventually loosening the connection.
• Pure aluminium has a tendency to creep under steady sustained pressure (to a greater degree as the temperature rises), again loosening the connection.
• Galvanic corrosion from the dissimilar metals increases the electrical resistance of the connection.

All of this resulted in overheated and loose connections, and this in turn resulted in some fires. Builders then became wary of using the wire, and many jurisdictions outlawed its use in very small sizes, in new construction. Yet newer fixtures were eventually introduced with connections designed to avoid loosening and overheating. At first they were marked "Al/Cu", but they now bear a "CO/ALR" coding.

Another way to forestall the heating problem is to crimp the short "Patch cable" of copper wire. A properly done high-pressure crimp by the proper tool is tight enough to reduce any thermal expansion of the aluminium. Today, new alloys, designs, and methods are used for aluminium wiring in combination with aluminium terminations.

Cast aluminium alloys use a four-to-five-digit number with a decimal point. The digit in the hundreds place indicates the alloying elements, while the digit after the decimal point indicates the form (cast shape or ingot).

-F : As fabricated
-H : Strain-hardened (cold worked) with or without thermal treatment

-H1 : Strain-hardened without thermal treatment

-H2 : Strain-hardened and partially annealed

-H3 : Strain-hardened and stabilized by low-temperature heating

-H4 : Strain-hardened, then lacquered/painted

: Second digit : A second digit denotes the degree of hardness

::-HX2 = 1/4 hard

::-HX4 = 1/2 hard

::-HX6 = 3/4 hard

::-HX8 = full hard

::-HX9 = extra hard

-T1 : Cooled from hot-working and naturally aged (at room temperature)

-T2 : Cooled from hot-working, cold-worked, and naturally aged

-T3 : Solution heat-treated and cold worked

-T4 : Solution heat-treated and naturally aged

-T5 : Cooled from hot-working and artificially aged (at elevated temperature)

: -T51 : Stress relieved by stretching

:: -T510 : No further straightening after stretching

:: -T511 : Minor straightening after stretching

: -T52 : Stress relieved by thermal treatment

-T6 : Solution heat-treated and artificially aged

: -T651 : Solution heat-treated, stress relieved by stretching, and artificially aged

-T7 : Solution heat-treated and stabilized

-T8 : Solution heat-treated, cold-worked, and artificially aged

-T9 : Solution heat-treated, artificially aged, and cold-worked

-T10 : Cooled from hot-working, cold-worked, and artificially aged

Note: -W is a relatively soft intermediary designation that applies after heat treat and before aging is completed. The -W condition can be extended at extremely low temperatures but not indefinitely and depending on the material will typically last no longer than 15 minutes at ambient temperatures.

"Metallic Materials Specification Handbook", p.1B-11
     

and are often cast from aluminium alloys. The most popular aluminium alloys used for cylinder blocks are A356, 319, and to a minor extent 242.

Aluminium alloys containing cerium are being developed and implemented in high-temperature automotive applications, such as and , and in other energy-generation applications. 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,"Cerium-Based, Intermetallic-Strengthened Aluminum Casting Alloy: High-Volume Co-product Development." Sims Z, Weiss D, McCall S et al. JOM, (2016), 1940–1947, 68(7). but gained attention for their strength at high temperatures over long periods of time."High performance aluminum-cerium alloys for high-temperature applications." Sims Z, Rios O, Weiss D et al. Materials Horizons, (2017), 1070–1078, 4(6). They gain strength from the presence of an Al₁₁Ce₃ intermetallic phase which is stable up to temperatures of 540 °C, and retains its strength up to 300 °C, making it quite viable at elevated temperatures. Aluminium–cerium alloys are typically cast, due to their excellent casting properties, although work has also been done to show that laser-based additive manufacturing techniques can be used as well to create parts with more complex geometries and greater mechanical properties."Evaluation of an Al-Ce alloy for laser additive manufacturing." Plotkowski A, Rios O, Sridharan N et al. Acta Materialia, (2017), 507–519, 126. 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."Cerium in aluminum alloys." Frank Czerwinski, J Mater Sci (2020) 55:24–72

• 7072 aluminium alloy
• 7116 aluminium alloy

• (2025). 9781498737173, CRC Press/Taylor & Francis Group. . ISBN 9781498737173
• Baykov Dmitry et al. Weldable aluminium alloys (in Russian); Leningrad, Sudpromgiz, 1959, 236 p.

• Aluminium alloys for die casting according to the Japanese Standards, China National Standards, U.S. Standards and German Standards
• Aluminium alloys for chill casting and low pressure casting according to the Japanese, Chinese, American and German industrial standard
• Aluminium alloys for extrusion according to the German Standards
• The Aluminium Association's chemical composition standards for wrought aluminium
• "The EAA Alumatter" computer-based reference database containing technical information on the most widely used aluminium alloys, their mechanical, physical and chemical properties
• Applications for Aluminium Alloys and Tempers
• Influence of Heat Treatment on the Mechanical Properties of Aluminium Alloy
• Aluminium: physical properties, characteristics and alloys