Stress and Strain Behaviours

My colleague has published a post making a general comparison of Steel, against, Aluminium. I will be looking to develop on this matter furthermore, so, as a group, we can be sure we're making the right choice.
As mentioned, mechanical properties vary from low strength alloys, to medium and high strength alloys. Regardless, there is no such aluminium alloy that compares to the strength of steel. But, as mentioned beforehand, strength is not alloys a deciding factor when selecting materials.

Below, there is a graph showing the stress strain curve (for, temperatures from -30c to 80c) you can see how each alloy, behaves very, very differently. Because of this, we shall have to select materials carefully.

Heat, does have a big factor also. Heat can have an impact from the weilding taking place in the manufacturing process, but also from the outdoor temperature. Aluminium's suffer more damage than Steel's, especially heat treated aluminium alloys. This results in lower actual strengths than metals in a stable environment.
(NB. If using mechanical fasteners, instead of weildings, there will be no heat damage)

As you can see from the above diagram, an important factor, steel is linearly elastic, up the 0.2% limit, however, aluminium, the proportional limit fp, is lower then fo.