All engineering metals are alloy's of some degree as the pure metals themselfs have often rather poor material properties. The basic principle of alloy's is that material properties are improved by enclosing elements (atoms, bubbles or "layers") of dissimilar metals inside the structure of the base metal. These enclosures pre tension the framework (through dislocations) that links all atoms to eachother and as such resist stretching or deformation by blocking reordering of the atom/molecule grid. Often they also change the chemical properties of the material, increasing corrosion resistance for example.
In effect alloys are a solution of the base metal with much lower quantities of dissimilar metals; a solution that has been frozen into a "fixed" state. However this state is not entirely "fixed", overtime and very slowly, these atoms/bubbles/dislocations may relocate themselfs or change the shape/size/composition. With it a significant portion of the alterations to the (alloy) material properties may occur.
This natural tendency to slow change over time is often much accellerated artificially during production to "soften" material or "pre-harden", i.e. to arrive at the exact desired material properties. This is the intent of heat treatments of alloys. It is then frozen down to a much much much slower speed so these properties are maintained within certain margins for many years.
Some alloys became softer over time other harden. Everything is possible depending on the initial state the solution was frozen into.
But shelf hardening is just non-sense. Because the same proces would also occur after the boat was sold. So if someone claims that selfhardening over say 3 years makes stock alu masts unfit for retail then they are also implicetly saying that the same stuff has become "worn-down" on a 3-year old boat as well. Not something customers want to hear.
Having said this, it is also not necessary on beach cat alu products like beams and masts. Nice stable alloys are currently available for that. The only item I came across that had significant aging problems were the alu castings on Prindles (hobies ?). And even then it would take 10 to 15 years to be significant (which is still not the same as unacceptable).
The only exception would be when certain manipulations were required to the items after being extruded. Certain machining activities and such, but still I have not found this to be a big issue with modern extruded alu alloys. Maybe Hobie has to do something to their beams that is an exception to this general rule but I wouldn't know what. With regard to mast I can't think of a single activity that would make building up masts problematic after say 5 or even 10 years.
I know that on modern designs with straight beams, straight V-ed dolphinstrikers and obviously straight masts; you don't need to do any machining after extruding, anodising and cutting them to length at the extruders yard. Pretty much all you need to do is to drill holes, rivet/bolt/screw parts into place and cut the sail entry slot. None of this is ever a problem.
