Density of aluminium
1 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.
Aluminium alloy 7075 is found at the top.
The commercial structural alloys is found
above the common mild steel [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]
2 The density of non-ferrous metals
Density of aluminum in comparison with the 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
3 Density of material
3.1 Density
Density of aluminium and any other material – it 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.
aluminum Density kg / m3 thousandfold, than g / secm3.
3.2 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.
3.3 Density dependence on temperature
The density of the material depends on the temperature. Typically, it decreases with increasing temperature. On the other hand, specific volume - volume per unit mass - increases with increasing temperature. This phenomenon is called thermal expansion. It is usually expressed as a coefficient of thermal expansion, which gives the change in length per degree of temperature, for example, mm / mm / ° C. Change in length is easier to measure and use, than the change in volume.
3.4 Specific volume
The specific volume of the material – this value, 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]
4 Density of aluminium
4.1 The theoretical density of aluminum
- 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].
4.2 Density of aluminum: solid and liquid
The graph of the dependence of the density of aluminum depending on temperature is shown in the figure below [1]:
- With increasing temperature decreases density of aluminum.
- decreases abruptly at the transition from solid aluminum in the liquid state its density with 2,55 to 2,34 g / cm3.
4.3 Influence of aluminum purity
The influence of the degree of purity of solid and liquid aluminum on its density is shown in the figure. 6.
Figure 4 – The density of solid and molten 99,996% aluminum (a – solid, b – molten) [3]
Figure 5 – The density of molten 99,996% aluminum [4]
Figure 6 – The influence of the degree of purity of solid and liquid aluminum on its density [3]
5 Aluminum alloys
5.1 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, other – 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 the figure. 7 [4].
Figure 7 – Influence of alloying elements on the density of aluminum alloys [4]
6 Lightest and heaviest aluminum alloys
- One of the lightest aluminum alloy is foreign casting alloy 518.0 (7,5-8,5 % magnesium) – 2,53 g per cubic centimeter [1].
- The heaviest aluminum alloys are foreign casting alloys 222.0 и 238.0 with a nominal copper content 10 %. Their nominal density – 2,95 g per cubic centimeter [1].
- Lightest deformable alloy – aluminum lithium alloy 8090 with nominal lithium content 2,0 %. Its nominal density – 2,55 g per cubic centimeter [1].
- The heaviest wrought aluminum alloy – alloy 7175: 2,85 g per cubic centimeter [4].
7 The density of industrial aluminum alloys
7.1 Grade Series
The density of aluminum and aluminum alloy, which are used in industry, presented in the table below for annealed condition (O). To a certain extent, it depends on the state of the alloy, especially for thermally hardenable aluminum alloys.
Figure 8 – 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.
