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Aluminium as a structural material

Design properties of aluminium


The density r of pure aluminium compares as follows with steel [1]:

Figure 1 –  Volume per unit weight of aluminium and other metals  [2]

Elastic constants

Modulus of elasticity

Aluminium is a springy metal with a relatively low modulus of elasticity (E). For the pure metal at room temperature it compares with steel as follows [1]:

Poisson’s ratio

Figure 2 – Plastic Yield Behaviour of Aluminium and Mild Steel [2]

Figure 3 – Comparison between four beams
which will give the same deflection [3]

Thermal properties

Thermal expansion

The coefficient of linear expansion a for pure aluminium at room temperature compares with steel as follows:

Thermal constants

Influence of elevated temperature

Influence of heat of welding

Figure 4 – Tensile Strength of 2014-T6 Tested at Room Temperature
after Exposure at Elevated Temperature [2]

Figure 5 – Reduction of strength in the heat affected zone (HAZ) (typical for EN AW-6082) [4]

More comparison of aluminium with steel

 The advantages



High corrosion resistance is due the fact that aluminium and aluminium alloys react with oxygen and water vapour in the air to produce a thin, compact oxide film which protects the underlying metal from further attack. So aluminium and most of the copper free alloys prove to be very corrosion resistant if the pH-value of any contact liquid lies between 5 and 8; with this range the most existing atmospheric/environmental conditions are covered [4].

 Extrusion process




 Low-temperature performance

Figure 6 – Tensile Properties of 6061 Alloy Heat Treated, Artifically Aged [2]

 The disadvantages



 Effect of temperature

 HAZ softening at welds


Aluminium components are more prone to failure by fatigue than are steel ones (Figure 7).

Thermal expansion

 Electrolytic corrosion


Figure 7 – Difference in Fatigue Behaviour between
Mild Steel and Aluminium Alloys [2]


  1. Aluminum Structures: A Guide to Their Specifications and Design – J. Randolph Kissell, Robert L. Ferry
  2. TALAT Lecture 1501
  3.  TALAT Lecture 2204
  4. R. Gitter  Design of Aluminium structures: Selection of Structural Alloys, EUROCODES – Background and Applications – 2008
  5. Eurocode 9 (EN 1999-1-1)
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