Aluminium Alloys

 

Aluminium is the third most plentiful element known to man, only oxygen and silicon exist in greater quantities. The element aluminium, chemical symbol Al, has the atomic number 13. 
Lightness is an essential property of aluminium. The metal has an atomic weight of 26.98 and a specific gravity of 2.70, approximately one-third the weight of other commonly used metals; with the exception of titanium and magnesium.
The electrical conductivity of 99.99% pure aluminium at 20°C is 63.8% of the
International Annealed Copper Standard (IACS). Because of its low mass density, the mass electrical conductivity of pure aluminium is more than twice that of annealed copper and greater than that of any other metal. The resistivity at 20°C is 2.69 uOhm cm. The electrical conductivity which is the reciprocal of
resistivity, is one of the more sensitive properties of aluminium being affected by both, changes in composition and thermal treatment. The addition of other metals in aluminium alloys lowers the electrical conductivity of the aluminium therefore this must be offset against any additional benefits which may be gained, such as an increase in strength. Heat treatment also affects the conductivity since elements in solid solution produce greater resistance than undissolved constituents.  

The thermal conductivity, κ, of 99.99% pure aluminium is 244 W/mK for the temperature range 0-1ß0°C which is 61.9% of the IACS, and again because of its low mass density  its mass thermal conductivity is twice that of copper. 

When exposed to air, a layer of aluminum oxide forms almost instantaneously on the surface of the aluminum. This layer has excellent resistance to corrosion. It is fairly resistant to most acids but less resistant to alkalis. Hence, aluminium has a higher resistance to corrosion than most other construction metals owing to the protection conferred by the thin but tenacious and very dense oxide film. This oxide layer is always present on the surface of aluminium in oxygen atmospheres. 

 

Solubility and associated effects of elements in aluminium

Mg, Cu, Ag, Zn and Si are alloying elements in aluminium, which have high solid solubility in the Al matrix.
In contrast, Cr, Mn and Zr are mainly used to form compounds to control grain structure.

 

Details on specific alloying elements:

 

Antimony occurs in trace amounts (0.01 to 0.1 ppm) primary in commercial aluminum. Antimony has very small solid solubility in aluminum (<0.01%). Some bearing alloys contain up to 4 to 6% Sb. Antimony can be used instead of bismuth to counteract hot cracking in aluminum-magnesium alloys.

 

Beryllium occurs in aluminum alloys containing magnesium to reduce oxidation at elevated temperatures. Up to 0.1% Be is used in aluminizing baths for steel to improve adhesion of the aluminum film and restrict the formation of the deleterious iron-aluminum complex.

 

Bismuth. The low-melting-point metals such as bismuth, lead, tin, and cadmium are added to aluminum to make free-machining alloys. These elements have a restricted solubility in solid aluminum and form a soft, low-melting phase that promotes chip breaking and helps to lubricate the cutting tool. An advantage of bismuth is that its expansion on solidification compensates for the shrinkage of lead. A 1-to-1 lead-bismuth ratio is used in the aluminum-copper alloy, 2011, and in the aluminum-Mg-Si alloy, 6262. Small additions of bismuth (20 to 200 ppm) can be added to aluminum-magnesium alloys to counteract the detrimental effect of sodium on hot cracking.

 

Boron is used as alloying element in aluminum and its alloys as a grain refining agent and for improving conductivity by precipitating vanadium, titanium, chromium, and molybdenum. Boron can be used alone (at levels of 0.005 to 0.1%) as a grain refiner during solidification, but becomes more effective when used with an excess of titanium. Commercial grain refiners commonly contain titanium and boron in a 5-to-l ratio.

 

Cadmium is a relatively low-melting element that finds limited use in aluminum. Up to 0.3% Cd may be added to aluminum-copper alloys to accelerate the rate of age hardening, increase strength, and increase corrosion resistance. At levels of 0.005 to 0.5%, it has been used to reduce the time of aging of aluminum-zinc-magnesium alloys.

 

Calcium has very low solubility in aluminum and forms the intermetallic CaAl4. An interesting group of alloys containing about 5% Ca and 5% Zn have superplastic properties. Calcium combines with silicon to form CaSi2, which is almost insoluble in aluminum and therefore will increase the conductivity of commercial-grade metal slightly. In aluminum-magnesium-silicon alloys, calcium will decrease age hardening. Its effect on aluminum-silicon alloys is to increase strength and decrease elongation, but it does not make these alloys heat treatable.

 

Carbon occurs in aluminium as an impurity element as oxycarbides and carbides, of which the most common is A14C3, but carbide formation with other impurities such as titanium is possible. A14C3 decomposes in the presence of water and water vapor, and this may lead to surface pitting.

 

Cerium, mostly in the form of mischmetal (rare earths with 50 to 60% Ce), has been added experimentally to casting alloys to increase fluidity and reduce die sticking.

 

Chromium occurs as a minor impurity in commercial-purity aluminum (5 to 50 ppm). It has a large effect on electrical resistivity. Chromium is a common addition to many alloys of the aluminum-magnesium, aluminum-magnesium-silicon, and aluminum-magnesium-zinc groups, in which it is added in amounts generally not exceeding 0.35%. In excess of these limits, it tends to form very coarse constituents with other impurities or additions such as manganese, iron, and titanium. Chromium has a slow diffusion rate and forms fine dispersed phases in wrought products. These dispersed phases inhibit nucleation and grain growth. Chromium is used to control grain structure, to prevent grain growth in aluminum-magnesium alloys, and to prevent recrystallization in aluminum-magnesium-silicon or aluminum-magnesium-zinc alloys during hot working or heat treatment. Chromium is thus mostly added to aluminum to control grain structure, to prevent grain growth in aluminum-magnesium alloys, and to prevent recrystallization in aluminum-magnesium-silicon or aluminum-magnesium-zinc alloys during heat treatment.  Chromium will also reduce stress corrosion susceptibility and improves toughness.

 

 

Cobalt is an uncommon addition to aluminum alloys. It has been added to some aluminum-silicon alloys containing iron, where it transforms the acicular ß (aluminum-iron-silicon) into a more rounded aluminum-cobalt-iron phase, thus improving strength and elongation. Aluminum-zinc-magnesium-copper alloys containing 0.2 to 1.9% Co are produced by powder metallurgy.

 

Copper. The aluminum-copper alloys typically contain between 2 to 10% copper, with smaller additions of other elements.  The copper provides substantial increases in strength and facilitates precipitation hardening.  The introduction of copper to aluminum can also reduce ductility and corrosion resistance.  The susceptibility to solidification cracking of aluminum-copper alloys is increased; consequently, some of these alloys can be the most challenging aluminum alloys to weld. These alloys include some of the highest strength heat treatable aluminum alloys. The most common applications for the 2xxx series alloys are aerospace, military vehicles and rocket fins.

 

Both cast and wrought aluminum-copper alloys respond to solution heat treatment and subsequent aging with an increase in strength and hardness and a decrease in elongation. The strengthening is maximum between 4 and 6% Cu, depending upon the influence of other constituents present.

 

Copper-magnesium. The main benefit of adding magnesium to aluminum-copper alloys is the increased strength possible following solution heat treatment and quenching. In wrought material of certain alloys of this type, an increase in strength accompanied by high ductility occurs on aging at room temperature. On artificial aging, a further increase in strength, especially in yield strength can be obtained, but at a substantial sacrifice in tensile elongation.

 

Copper-magnesium plus other elements. The cast aluminum-copper-magnesium alloys containing iron are characterized by dimensional stability and improved bearing characteristics, as well as by high strength and hardness at elevated temperatures. However, in a wrought Al-4%Cu-0.5%Mg alloy, iron in concentrations as low as 0.5% lowers the tensile properties in the heat-treated condition, if the silicon content is less than that required to tie up the iron as the aFeSi constituent.

 

Gallium is an impurity in aluminum and is usually present at levels of 0.001 to 0.02%. At these levels its effect on mechanical properties is quite small. At the 0.2% level, gallium has been found to affect the corrosion characteristics and the response to etching and brightening of some alloys.

 

Hydrogen has a higher solubility in the liquid state at the melting point than in the solid at the same temperature. Because of this, gas porosity can form during solidification. Hydrogen is produced by the reduction of water vapor in the atmosphere by aluminum and by the decomposition of hydrocarbons. In addition to causing primary porosity in casting, hydrogen causes secondary porosity, blistering, and high-temperature deterioration (advanced internal gas precipitation) during heat treating. It probably plays a role in grain-boundary decohesion during stress-corrosion cracking. Its level in melts is controlled by fluxing with hydrogen-free gases or by vacuum degassing.

 

Indium. Small amounts (0.05 to 0.2%) of indium have a marked influence on the age hardening of aluminum-copper alloys, particularly at low copper contents (2 to 3% Cu).

 

Iron is the most common impurity found in aluminum. It has a high solubility in molten aluminum and is therefore easily dissolved at all molten stages of production. The solubility of iron in the solid state is very low (~0.04%) and therefore, most of the iron present in aluminum over this amount appears as an intermetallic second phase in combination with aluminum and often other elements.

 

Lead. Normally present only as a trace element in commercial-purity aluminum, lead is added at about the 0.5% level with the same amount as bismuth in some alloys (2011 and 6262) to improve machinability.

 

Lithium. The addition of lithium to aluminum can substantially increase strength and, Young’s modulus, provide precipitation hardening and decreases density.

 

The impurity level of lithium is of the order of a few ppm, but at a level of less than 5 ppm it can promote the discoloration (blue corrosion) of aluminum foil under humid conditions. Traces of lithium greatly increase the oxidation rate of molten aluminum and alter the surface characteristics of wrought products.

 

Magnesium is the major alloying element in the 5xxx series of alloys. Its maximum solid solubility in aluminum is 17.4%, but the magnesium content in current wrought alloys does not exceed 5.5%. The addition of magnesium markedly increases the strength of aluminum without unduly decreasing the ductility. Corrosion resistance and weldability are good.

The addition of magnesium to aluminum increases strength through solid solution strengthening and improves their strain hardening ability.  These alloys are the highest strength nonheat-treatable aluminum alloys and are, therefore, used extensively for structural applications. The 5xxx series alloys are produced mainly as sheet and plate and only occasionally as extrusions.  The reason for this is that these alloys strain harden quickly and, are, therefore difficult and expensive to extrude.  Some common applications for the 5xxx series alloys are truck and train bodies, buildings, armored vehicles, ship and boat building, chemical tankers, pressure vessels and cryogenic tanks.

 

 

Magnesium-Manganese. In wrought alloys, this system has high strength in the work-hardened condition, high resistance to corrosion, and good welding characteristics. Increasing amounts of either magnesium or manganese intensify the difficulty of fabrication and increase the tendency toward cracking during hot rolling, particularly if traces of sodium are present.

 

Magnesium-Silicon.  The addition of both, magnesium and silicon to aluminum produces the compound magnesium-silicide (Mg2Si).  The formation of this compound provides the 6xxx series their heat-treatability.  The 6xxx series alloys are easily and economically extruded and for this reason are most often found in an extensive selection of extruded shapes.   These alloys form an important complementary system with the 5xxx series alloy.  The 5xxx series alloy used in the form of plate and the 6xxx are often joined to the plate in some extruded form.  Some of the common applications for the 6xxx series alloys are handrails, drive shafts, automotive frame sections, bicycle frames, tubular lawn furniture, scaffolding, stiffeners and braces used on trucks, boats and many other structural fabrications. Wrought alloys of the 6xxx group contain up to 1.5% each of magnesium and silicon in the approximate ratio to form Mg2Si, that is, 1.73:1. The maximum solubility of Mg2Si is 1.85%, and this decreases with temperature. Precipitation upon age hardening occurs by formation of Guinier-Preston zones and a very fine precipitate. Both confer an increase in strength to these alloys, though not as great as in the case of the 2xxx or the 7xxx alloys.

 

Manganese. The addition of manganese to aluminum (3xxx ) increases strength somewhat through solution strengthening and improves strain hardening while not appreciably reducing ductility or corrosion resistance. These are moderate strength nonheat-treatable materials that retain strength at elevated temperatures and are seldom used for major structural applications.  The most common applications for the 3xxx series alloys are cooking utensils, radiators, air conditioning condensers, evaporators, heat exchangers and associated piping systems. The element is also a common impurity in primary aluminum, in which its concentration normally ranges from 5 to 50 ppm. It decreases resistivity. Manganese increases strength either in solid solution or as a finely precipitated intermetallic phase. It has no adverse effect on corrosion resistance. Manganese has a very limited solid solubility in aluminum in the presence of normal impurities but remains in solution when chill cast so that most of the manganese added is substantially retained in solution, even in large ingots.

 

Mercury has been used at the level of 0.05% in sacrificial anodes used to protect steel structures. Other than for this use, mercury in aluminum or in contact with it as a metal or a salt will cause rapid corrosion of most aluminum alloys.

 

Molybdenum is a very low level (0.1 to 1.0 ppm) impurity in aluminum. It has been used at a concentration of 0.3% as a grain refiner, because the aluminum end of the equilibrium diagram is peritectic, and also as a modifier for the iron constituents, but it is not in current use for these purposes.

 

Nickel. The solid solubility of nickel in aluminum does not exceed 0.04%. Over this amount, it is present as an insoluble intermetallic, usually in combination with iron. Nickel (up to 2%) increases the strength of high-purity aluminum but reduces ductility. Binary aluminum-nickel alloys are no longer in use but nickel is added to aluminum-copper and to aluminum-silicon alloys to improve hardness and strength at elevated temperatures and to reduce the coefficient of expansion.

 

Niobium. As with other elements forming a peritectic reaction, niobium would be expected to have a grain refining effect on casting. It has been used for this purpose, but the effect is not marked.

 

Phosphorus is a minor impurity (1 to 10 ppm) in commercial-grade aluminum. Its solubility in molten aluminum is very low (~0.01% at 660oC) and considerably smaller in the solid.

 

Silicon. The addition of silicon to aluminum (4xxxreduces melting temperature and improves fluidity. Silicon alone in aluminum produces a nonheat-treatable alloy; however, in combination with magnesium it produces a precipitation hardening heat-treatable alloy.  Consequently, there are both heat-treatable and nonheat-treatable alloys within the 4xxx series.  Silicon additions to aluminum are commonly used for the manufacturing of castings.  The most common applications for the 4xxx series alloys are filler wires for fusion welding and brazing of aluminum. After iron, Si is the highest impurity level in electrolytic commercial aluminum (0.01 to 0.15%). In wrought alloys, silicon is used with magnesium at levels up to 1.5% to produce Mg2Si in the 6xxx series of heat-treatable alloys.

 

Titanium. Titanium is added to aluminum primarily as a grain refiner.  The grain refining effect of titanium is enhanced if boron is present in the melt or if it is added as a master alloy containing boron largely combined as TiB2.  Titanium is a common addition to aluminum weld filler wire as it refines the weld structure and helps to prevent weld cracking.

 

 

Vanadium. There is usually 10 to 200 ppm V in commercial-grade aluminum, and because it lowers conductivity, it generally is precipitated from electrical conductor alloys with boron.

 

Zinc. The aluminum-zinc alloys (7xxx) have been known for many years, but hot cracking of the casting alloys and the susceptibility to stress-corrosion cracking of the wrought alloys curtailed their use. Aluminum-zinc alloys containing other elements offer the highest combination of tensile properties in wrought aluminum alloys. The addition of zinc to aluminum (in conjunction with some other elements, primarily magnesium and/or copper) produces heat-treatable aluminum alloys of the highest strength.  The zinc substantially increases strength and permits precipitation hardening.  Some of these alloys can be susceptible to stress corrosion cracking and for this reason are not usually fusion welded.  Other alloys within this series are often fusion welded with excellent results.  Some of the common applications of the 7xxx series alloys are aerospace, armored vehicles, baseball bats and bicycle frames.

 

 

Zinc-Magnesium. The addition of magnesium to the aluminum-zinc alloys develops the strength potential of this alloy system, especially in the range of 3 to 7,5% Zn. Magnesium and zinc form MgZn2, which produces a far greater response to heat treatment than occurs in the binary aluminum-zinc system. The strength of the wrought aluminum-zinc alloys also is substantially improved by the addition of magnesium. Increasing the MgZn2, concentration from 0.5 to 12% in cold-water quenched 1.6 mm sheet continuously increases the tensile and yield strengths. The addition of magnesium in excess (100 and 200%) of that required to form MgZn2 further increases tensile strength.

Zinc-Magnesium-Copper. The addition of copper to the aluminum-zinc-magnesium system, together with small but important amounts of chromium and manganese, results in the highest-strength aluminum-base alloys commercially available. In this alloy system, zinc and magnesium control the aging process. The effect of copper is to increase the aging rate by increasing the degree of supersaturation and perhaps through nucleation of the CuMgAl2 phase. Copper also increases quench sensitivity upon heat treatment. In general, copper reduces the resistance to general corrosion of aluminum-zinc-magnesium alloys, but increases the resistance to stress corrosion. The minor alloy additions, such as chromium and zirconium, have a marked effect on mechanical properties and corrosion resistance.

 

Zirconium additions in the range 0.1 to 0.3% are used to form a fine intermetallic precipitate that inhibits recovery and recrystallization. An increasing number of alloys, particularly in the aluminum-zinc-magnesium family, use zirconium additions to increase the recrystallization temperature and to control the grain structure in wrought products.

 

Specifications and types of Aluminium alloys


In aluminum specifications, a four-digit index system is used for the designation of cast and wrought aluminum alloys.
These two classes of aluminum alloys can be further subdivided into families of alloys based on chemical composition and on temper designation.

Pure aluminum is mechancially very soft and hence typcially alloyed with many other elements to synthesize a range of materials with a vast variety of physical and mechanical properties.

The alloying elements are used as the nomenclature basis to group aluminum alloys into two types of categories: non-heat-treatable and heat-treatable aluminum alloys.

 

Most aluminum specifications currently in use designate aluminum alloys in the following way:

 

First digit – principal alloying constituent(s),
Second digit – variations of initial alloy,
Third and fourth digits – individual alloy variations (number has no significance but is unique).


Wrought Aluminum Specifications. The wrought alloy group is shown as: 1xxx-pure Al (99.00% or greater); 2xxx-Al-Cu alloys; 3xxx-Al-Mn alloys; 4xxx-Al-Si alloys; 5xxx-Al-Mg alloys; 6xxx-Al-Mg-Si alloys.

 

Cast Aluminum Specifications. The designation system and specifications for cast aluminum alloys are similar in some respects to that of wrought alloys. The cast alloy designation system also has four digits and the first digit specifies the major alloying constituent(s). However, a decimal point is used between the third and fourth digits to make clear that these are designations used to identify alloys in the form of castings (0) or foundry ingot (1,2).

A letter before the numerical designation indicates a modification of the original alloy or an impurity limit. These serial letters are assigned in alphabetical sequence starting with A, but omitting I,O,Q and X, with X being reserved for experimental alloys.

The cast alloy group is shown as: 1xx.x-Pure Al (99.00% or greater), 2xx.x Al-Cu alloys; 3xx.x Al-Si + Cu and/or Mg; 4xx.x Al-Si; 5xx.x Al-Mg; 7xx.x – Al-Zn; 8xx.x- Al-Sn; 9xx.x-Al+Other elements and 6xx.x unused series.

 

Aluminum Alloy Temper-Designation System. Tempering treatments are essential for aluminum specifications due to their crucial influence on the material properties. The temper designation system is based on the sequences of mechanical or thermal treatments, or both, used to produce the various temper treatments. The temper designation is always presented immediately following the alloy designation with a hyphen between the designation and the temper (e.g.2014-T6, 3003-H14, 1350-H19 (extra hard) etc.). The first character in the temper designation is a capital letter indicating the general class of treatment such as: F-as fabricated; O-annealed; H-strain hardened; W-solution heat treated and T-thermally treated to produce stable tempers other than F,O, or H. Note that the temper designations differ between non heat-treatable alloys and heat-treatable alloys and their meanings are given below.

 

Non Heat-Treatable Aluminum Alloys. The letter "H" is always followed by 2 or 3 digits. The first digit indicates the particular method used to obtain the temper as follows: H1-means strain hardened only, H2-means strain hardened, then partially annealed and H3-means strain hardened, then stabilized. The temper is indicated by the second digit as follows: 2-1/4 hard; 4-1/2 hard; 6-3/4 hard; 8-full hard and 9-extra hard which means that added digits indicate modification of standard practice. The non heat-treatable alloys are mainly found in the 1xxx, 3xxx, 4xxx, and 5xxx alloys series depending upon their major alloying elements.

 

Heat-Treatable Aluminum Alloys (e.g. F, O or T): The letter "T" is always followed by one or more digits. These digits indicate the method used to produce the stable tempers, as follows: T3-Solution heat treated and then cold worked, T4-Solution heat treated and then naturally aged, T5-Artificially aged only, T6-Solution heat treated and then artificially aged etc. The heat-treatable alloys are found primarily in the 2xxx, 6xxx and 7xxx alloys series.

 

In short one also could express hardness as:

H_1    1/8 hard

H_2    1/4 hard

H_3    3/8 hard

H_4    1/2 hard

H_5    5/8 hard

H_6    3/4 hard    

H_7    7/8 hard    

H_8    Full hard

 

 

Heat Treatable Aluminium Alloy Temper Designations

Designation

Description

Application

O

Annealed, Recrystalized

Lowest Strength, High ductility

F

As Fabricated

Fabrication with no special control over thermal or strain hardening

W

Solution Heat Treatment

Unstable temper application with subsequent period of natural age

T1

 

Cooled and naturally aged, i.e. Cooled after being shaped to its final dimensions during a process involving a lot of  heat (such as extrusion), then naturally aged to a stable condition.

 

T2

 

Cooled, cold worked & Naturally aged, i.e. cooled after being shaped to its final dimensions during a process involving a lot of heat 
          (such as extrusion), then cold worked.

T3

 

Solution heat treated, cold worked  & naturally aged.

T4

 

Solution heat treated & naturally aged

T5

 

Cooled and artificially aged, i.e. more specific, cooled after being shaped to its final dimensions during a process involving a lot of heat
         (such as extrusion), then artificially aged. T5 is T1 that has been artificially aged.

T6

 

Solution heat treated and Stabilized, i.e. solution heat treated and artificially aged to a stable condition. T6 is T4 that  has been artificially aged.

T7

 

Solution heat treated, stabilized to provide special property, i.e. solution heat treated and naturally aged past the point of a stable condition. This process provides control of some special characteristics.

T8

 

Solution heat treated, cold worked, artificially aged

T9

 

Solution heat treated, artificially aged, then cold worked

T10

 

Cooled, cold worked, then artificially aged, i.e. cooled after being shaped to its final dimensions during a process involving a lot of  heat 
         (such as extrusion), then cold worked and artificially aged. T10 is T2 that has been artificially 

 


Wrought Aluminium alloys (85%)


Non-heat-treatable Al alloys

 

High-purity Al alloys (1xxx series)
Al-Mn and Al-Mn-Mg alloys (3xxx series)
Al-Mg alloys (5xxxx series)

 

Heat-treatable alloys (respond to strengthening by heat treatment)
Al-Cu alloys (2xxxx series)
Al-Cu-Mg alloys (2xxxx series)
Al-Mg-Si alloys (6xxxx series)
Al-Zn-Mg and Al-Zn-Mg-Cu alloys (7xxxx series)

 

 

Cast alloys
 

Al-Si alloys
Al-Cu alloys
Al-Mg alloys
Al-Zn-Mg alloys

Details on commercially used Aluminium alloy grades

Aluminum Grades Series 1xxx

These types of aluminum (1050, 1060, 1100, 1145, 1200, 1230, 1350 etc.) are characterized by excellent corrosion resistance, high thermal and electrical conductivities, low mechanical properties, and excellent workability. Moderate increases in strength may be obtained by strain hardening. Iron and silicon are the major impurities.

 

Aluminum Grades Series 2xxx

The aluminum 2xxx alloy series (2011, 2014, 2017, 2018, 2124, 2219, 2319, 201.0; 203.0; 206.0; 224.0; 242.0 etc.) require solution heat treatment to obtain optimum properties; in the solution heat-treated condition, mechanical properties are similar to, and sometimes exceed, those of low-carbon steel. In some instances, precipitation heat treatment (aging) is employed to further increase mechanical properties. This treatment increases yield strength, with attendant loss in elongation; its effect on tensile strength is not as great.

The aluminum alloys in the 2xxx series do not have as good corrosion resistance as most other aluminum alloys, and under certain conditions they may be subject to intergranular corrosion. Aluminum grades in the 2xxx series are good for parts requiring good strength at temperatures up to 150°C (300°F). Except for the grade 2219, these aluminum alloys have limited weldability, but some alloys in this series have superior machinability. Aluminum grade 2024 is the most popular alloy and is commonly used in aircraft construction.

 

Aluminum Grades Series 3xxx

These types of alloys (3003, 3004, 3105, 383.0; 385.0; A360; 390.0) generally are non-heat treatable but have about 20% more strength than 1xxx series aluminum alloys. Because only a limited percentage of manganese (up to about 1.5%) can be effectively added to aluminum, manganese is used as a major element in only a few alloys.

 

Aluminum Grades Series 4xxx

The major alloying element in 4xxx series alloys (4032, 4043, 4145, 4643 etc.) is silicon, which can be added in sufficient quantities (up to 12%) to cause substantial lowering of the melting range. For this reason, aluminum-silicon alloys are used in welding wire and as brazing alloys for joining aluminum, where a lower melting range than that of the base metal is required. The aluminum alloys containing appreciable amounts of silicon become dark gray to charcoal when anodic oxide finishes are applied and hence are in demand for architectural applications.

 

Aluminum Grades Series 5xxx

The major alloying element is magnesium; when it is used as a major alloying element or with manganese, the result is a moderate-to-high-strength work-hardenable alloy. Magnesium is considerably more effective than manganese as a hardener – about 0.8% Mg being equal to 1.25% Mn – and it can be added in considerably higher quantities. Aluminum alloys in this series (5005, 5052, 5083, 5086, etc.) possess good welding characteristics and relatively good resistance to corrosion in marine atmospheres. However, limitations should be placed on the amount of cold work and the operating temperatures (150°F) permissible for the higher-magnesium aluminum alloys to avoid susceptibility to stress-corrosion cracking.

 

Aluminum Grades Series 6xxx

Aluminum alloys in the 6xxx series (6061, 6063) contain silicon and magnesium approximately in the proportions required for formation of magnesium silicide (Mg2Si), thus making them heat treatable. Although not as strong as most 2xxx and 7xxx alloys, 6xxx series aluminum alloys have good formability, weldability, machinability, and relatively good corrosion resistance, with medium strength. Aluminum grades in this heat-treatable group may be formed in the T4 temper (solution heat treated but not precipitation heat treated) and strengthened after forming to full T6 properties by precipitation heat treatment.

 

Aluminum Grades Series 7xxx

Zinc, in amounts of 1 to 8% is the major alloying element in 7xxx series aluminum alloys (7075, 7050, 7049, 710.0; 711.0 etc.), and when coupled with a smaller percentage of magnesium results in heat-treatable alloys of moderate to very high strength. Usually other elements, such as copper and chromium, are also added in small quantities. 7xxx series alloys are used in airframe structures, mobile equipment, and other highly stressed parts. Higher strength 7xxx aluminum alloys exhibit reduced resistance to stress corrosion cracking and are often utilized in a slightly overaged temper to provide better combinations of strength, corrosion resistance, and fracture toughness.

 

Aluminum Grades Series 8xxx

The 8xxx series (8006; 8111; 8079; 850.0; 851.0; 852.0) is reserved for alloying elements other than those used for series 2xxx to 7xxx. Iron and nickel are used to increase strength without significant loss in electrical conductivity, and so are useful in such conductor alloys as 8017. Aluminum-lithium alloy 8090, which has exceptionally high strength and stiffness, was developed for aerospace applications. Aluminum alloys in the 8000 series correspond to Unified Numbering System A98XXX etc.

 

 

 

Mechanical properties of some selected commercial aluminium alloys

 

Alloy

Temper

Proof Stress 0.2% (MPa)

Tensile Strength (MPa)

Shear Strength (MPa)

Elongation A5 (%)

Hardness Vickers (HV)

AA1050A

H12

H14

H16

H18

0

85

105

120

140

35

100

115

130

150

80

60

70

80

85

50

12

10

7

6

42

30

36

-

44

20

AA2011

T3

T6

290

300

365

395

220

235

15

12

100

115

AA3103

H14

0

140

45

155

105

90

70

9

29

46

29

AA4015

0

H12

H14

H16

H18

45

110

135

155

180

110-150

135-175

160-200

185-225

210-250

-

-

-

-

-

20

4

3

2

2

30-40

45-55

-

-

-

AA5083

H32

0/H111

240

145

330

300

185

175

17

23

95

75

AA5251

H22

H24

H26

0

165

190

215

80

210

230

255

180

125

135

145

115

14

13

9

26

65

70

75

46

AA5754

H22

H24

H26

0

185

215

245

100

245

270

290

215

150

160

170

140

15

14

10

25

75

80

85

55

AA6063

0

T4

T6

50

90

210

100

160

245

70

11

150

27

21

14

85

50

80

AA6082

0

T4

T6

60

170

310

130

260

340

85

170

210

27

19

11

35

75

100

AA6262

T6

T9

240

330

290

360

-

-

8

3

-

-

AA7075

0

T6

105-145

435-505

225-275

510-570

150

350

9

5

65

160

 

 

Acta Mat. 2011, 59, p. 364