The properties of aluminum alloys

for any aluminum properties and aluminum alloys are they so willingly used in all industries and construction?

corrosion resistance

The thin natural oxide film, which firmly "engages" with the parent metal, It provides many aluminum alloys a significant corrosion resistance in many atmospheric and chemical environments. Especially distinguished in this series alloys 1xxx, 3xxx, 5xxx and 6xxx.

Figure 1 – The influence of alloying elements of aluminum alloys
for their corrosion resistance and fatigue strength [3]

Thermal conductivity

Aluminum and aluminum alloys are good conductors of heat. The thermal conductivity of aluminum alloy is more than four times higher, than that of carbon steels. They begin to melt at a much lower temperature, than steel. The melting point of pure aluminum is about 660 ° C, and aluminum alloys depending on the degree of alloying begin to melt at lower temperatures, for example, at 515 ° C for alloy 2017 (D1).

Figure 2 – Thermal conductivity of aluminum in comparison with other metals [3]

conductivity

Pure aluminum and some of its alloys have very high electrical conductivity (low electrical resistance), second only to metals including copper, which are used as electricity conductors. At the same time, on the high-voltage power lines, if it allows the degree of air pollution of the atmosphere, use it aluminum wires. They have a larger cross-section, than the equivalent copper wire, however, less weight and twice, What allow, in particular, less put the support and reduce their height.

Figure 3 – Electrical properties of aluminum [3]

Strength to weight ratio

The high ratio of strength / weight - relatively high strength at low density – determines the high efficiency of aluminum alloys and opens up many opportunities for replacing heavier metals without loss (and perhaps with an increase) in the bearing capacity of a product or part. This feature of the aluminum alloys in combination with a good corrosion resistance, and the ability to complete processing after the end of its life, provides them with widespread use in the production of containers and in transport engineering (aircraft, cars, passenger cars).

Figure 4 – Volume per unit weight of aluminum compared to other metals [3]

Aluminum at low temperatures

Aluminum alloys, especially alloys series 3xxx, 5xxx and 6xxx ideally suited for operation at low temperatures. Numerous data confirm, their ductility and toughness, as well as strength, above at low temperatures, down to absolute zero, than at "room" temperature.

Figure 5 – Mechanical properties of the aluminum alloy 6061 (AD33),
heat-treated, artificially aged [3]

technological processing

Aluminum alloys are easily processed by most known metal processing technologies, and particularly easily pressed. Compression is the process of forcing hot metal through the die, forming profiles with complex cross-sections. Sometimes, This process is known as a more appropriate name - Extrusion. This property of aluminum alloys makes it possible to produce profiles of them with a virtually unlimited variety of cross-sectional shapes. This allows you to have the metal in those areas and thus, to ensure that the profile of the maximum load-bearing capacity under the influence of the given loads.

Methods aluminum compound

Details of aluminum alloy are joined by a large number of ways, including, quarrel, rations, riveting, screw connections, not to mention a wide variety of mechanical methods. welding of aluminum it may seem difficult for those, who has experience only with steels and try to move it to the aluminum. Welding of aluminum alloys is considered a fairly easy, when used proven techniques such, as consumable electrode (MIG) and tungsten non-consumable electrode (TIG) arc welding in inert gas.

Recycling scrap

An important characteristic of the alloys is aluminum, that their life cycle is almost completely closed – they are easy to reuse – retsiklingu – and, Unlike other construction materials, they are processed almost the same high-quality products.

Figure 5 – Line for recycling used aluminum cans
into ingots for rolling a thin sheet to make new cans [3]

Typical properties and normalized

data on aluminum properties and aluminum alloy, as well as other industrial materials, are of two main types:

  • typical (nominal) and
  • normalized (limit).

Typical physical properties

Physical properties, such as the:

  • coefficient of thermal expansion,
  • coefficient of thermal conductivity,
  • electrical conductivity,
  • electrical resistance and even
  • density

almost always typical values. They are obtained from laboratory testing of representative commercial batches of products.

typical physical properties of aluminum alloys used as a basis for comparison alloys and their states and not be used for engineering calculations.

Typical physical properties are not guaranteed values, since in most cases they represent the average values ​​for products with different sizes, forms, and methods of manufacture and can not be exactly representative of the products of all sizes and shapes.

Typical mechanical properties

Mechanical properties may be typical, and normalized.

Typical values ​​for mechanical properties:

  • tensile strength,
  • yield strength,
  • extension,
  • hardness,
  • fatigue strength

- it's theirs average or median meaning near the peak of the distribution functions.

Figure 6 – The influence of alloying elements on the tensile strength, hardness,
notch sensitivity and ductility [3]

Figure 7 – The influence of alloying elements of aluminum alloys
on their density and modulus of elasticity (Young's modulus) [3]

Figure 8 – The difference phenomena of fatigue
between low carbon steel and aluminum alloys [3]

These distribution functions are obtained by processing the results of standard tests of samples of samples from many industrial batches. Typical values ​​are representative of products with an average thickness or cross-section. They are most suited to demonstrate the relationship between states and their alloys. However, these data are not suitable for strength analysis of structures and components. So, typical values ​​of tensile strength, for example, do not include their higher values ​​(by 5-10 % higher), inherent in thin extrusions, and lower values, which are characteristic for very thick, thermally hardened products.

Normalized mechanical properties

For strength calculations of structures and parts, normalized (limiting) values ​​of mechanical properties are used. Normalized value - this value, characterizing the properties of the material or product, which has a certain probability of not exceeding with unlimited test series. This is a numeric value, usually corresponds to a particular quantile received statistical distribution of the material or product.

The limiting value of the mechanical properties is generally set on the basis of the principle, Whereby 99 % material products games match it with the probability 0,95. In most cases, these limit values ​​are based on a normal distribution of data. Limit values ​​of mechanical properties is generally used to calculate or details of structures, as well as the acceptance of commercial batches.

Averaged mechanical properties

Some strength parameters of the material (for example, elastic modulus, creep factor, coefficient of thermal expansion) are used in strength calculations and in the form of typical, averaged values. In some cases, for example, when assessing the sustainability of, use a lower or a higher elastic modulus relative to its average value.

Sources:
1. Aluminium and Aluminium Alloys. – ASM International, 1993.
2. EN1990:2002 Eurocode 0: Basis of structural design.
3. TALAT 1501