AluminiumAluminium properties

Density of aluminium

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Learn about the advantages of low density of aluminium. Find out how it contributes to its strength and cost-effectiveness compared to other metals.

Lightweight structural metal

Low density is one of the main advantages of aluminum over other structural metals.

Figure 1 – Density-Related Strength of Aluminium in
Comparision with Various Metals and Alloys [1]

Figure 2 – Volume per Unit Weight of Various Metals.
It is important to compare the cost of aluminium with other materials on this basis [1]

The density of non-ferrous metals

Density of aluminum in comparison with density of other light metals:

  • aluminum: 2,70 g / cm3
  • titanium: 4,51 g / cm3
  • magnesium: 1,74 g / cm3
  • beryllium: 1,85 g / cm3

Density of a material

Density

Density of aluminium and any other material is a physical quantity, determining the mass ratio of the material to the occupied volume.

  • The unit of density measurement in the SI dimension adopted: kg / m3.
  • For the density of aluminum is often used more visual dimension: g / cm3.

For an example: 2700  kg / m3 = 2,7 ton / m3 = 2,7 g / cm3 

Specific gravity

To estimate the amount of material per unit volume is often used such a system does not, but more visual unit as “proportion”. Unlike density specific gravity is not an absolute unit of measurement. The thing is, it depends on the magnitude of the gravitational acceleration g, which varies depending on the location on Earth.

Temperature dependence

  • Density of materials depends on temperature. Typically, it decreases with increasing temperature.
  • Specific volume (volume per unit mass) increases with increasing temperature. This phenomenon is called thermal expansion.
  • Thermal expansionIt is usually expressed as the coefficient of thermal expansion. It gives the change in length per degree of temperature, for example, mm / mm / ° C.

Specific volume

The specific volume of a material is the quantity, inverse density. It indicates the amount of mass and per unit volume is of dimension m3/kg. According to the specific volume of material it is convenient to observe during the heating-cooling change the density of materials.

The figure below shows the change in the specific volume of various materials (pure metal, alloy and amorphous material) with increasing temperature. Flat areas schedules – is the thermal expansion of all types of materials in the solid and liquid state. When pure metal melts, there is a jump in the increase in specific volume (decrease in density), the alloy melting – rapid increase as its melting temperature range in. Amorphous materials upon melting (at the glass transition temperature) increase their coefficient of thermal expansion [2].

 Figure 3 – Changes in volume per unit weight (1/density)
as a function of temperature for a pure metal, alloy, and glass [2]

Density of pure aluminium

Theoretical density of aluminium

  • The theoretical room-temperature (20 “C) density based on lattice spacing is 2698,72 kg/m3
  • Experimental values range from 2696,6 to 2698,8 kg/m3 for polycrystalline material with the densities of single crystals lying 0.34% higher [1].

Density of aluminium: solid and liquid

The graph of the dependence of the density of aluminium depending on temperature is shown in Figure 4 [1]:

  • Decreases slow with increasing temperature.
  • Decreases abruptly at the transition from solid aluminium in the liquid state its density with 2,55 to 2,34 g / cm3.

Influence of aluminium purity

The influence of the degree of purity of solid and liquid aluminum on its density is shown in Figure 5.


Figure 4 – The density of solid and molten 99,996% aluminium (a – solid, b – molten) [3]

 

Figure 5 – The influence of the degree of purity of solid and liquid aluminum on its density [3]

Density of aluminium alloys

The effect of alloying

Differences in the density of different aluminum alloys caused by the fact, they contain different alloying elements in the different amounts. On the other hand, Some alloying elements lighter than aluminum, others are heavier.

Alloying elements are lighter than aluminum:

  • silicon (2.33 g / cm³),
  • magnesium (1.74 g / cm³),
  • lithium (0.533 g / cm³).

Alloying elements are heavier than aluminum:

  • iron (7.87 g / cm³),
  • manganese (7.40 g / cm³),
  • copper (8.96 g / cm³),
  • zinc (7.13 g / cm³).

The influence of alloying elements on the density of aluminum alloys is shown in Figure 6 [4].

 

Figure 6– The influence of alloying elements on density of aluminium alloys [4]

Lightest and heaviest aluminium alloys

  • One of the lightest aluminium alloy is the casting alloy 518.0 (7,5-8,5 % magnesium) – 2,53 g per cubic centimeter [1].
  • The heaviest aluminum alloys are the casting alloys 222.0 и 238.0 with the nominal copper content 10 %. Their nominal density is 2,95 g per cubic centimeter [1].
  • The lightest wrought alloy is aluminum-lithium alloy 8090 with nominal lithium content 2,0 %. Its nominal density is 2,55 g per cubic centimeter [1].
  • The heaviest wrought aluminum alloy is 7175: 2,85 g per cubic centimeter [4].

The density of industrial aluminum alloys

7.1 Grade Series

The density of aluminium and aluminium alloy, which are used in industry, presented in Figure 7 for annealed condition (O). To a certain extent, it depends on the state of the alloy, especially for thermally hardenable aluminum alloys.

Figure 7 – The Effect of Alloying Elements on Density and Young’s Modulus [1]

7.2 Aluminum-lithium alloys

The most famous are low density aluminum-lithium alloys.

  • Lithium is the lightest metal element.
  • Lithium density at room temperature is 0,533 g/cm³ – this metal can float in water!
  • Each 1 % lithium aluminum decreases its density 3 %
  • Each 1 % lithium aluminum increases the modulus of elasticity in 6 %. It is very important for the aircraft and space technology.

Popular industrial aluminum-lithium alloys are alloys 2090, 2091 и 8090:

  • Nominal content of lithium in the alloy 2090 is 1,3 %, and a nominal density of – 2,59 g / cm3.
  • In the alloy 2091 nominal content of lithium 2,2 %, and a nominal density of – 2,58 g / cm3.
  • In the alloy 8090 when the content of lithium 2,0 % density is 2,55 g / cm3.

Annex A

Table A1 – Nominal density of wrought aluminum alloys [4]

Sources:

1. TALAT 1501

2. FUNDAMENTALS OF MODERN MANUFACTURING – Materials, Processes, and Systems /Mikell P. Groover – JOHN WILEY & SONS, INC., 2010

3.  Properties of Pure Aluminum / A. Sverdlin // Handbook of Aluminum, Volume 1: Physical Metallurgy and Processes – 2003.

4. Aluminum and Aluminum Alloys, ASM International, 1993.

 

 

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