[8-Ball]

Again, you need to be careful. Aluminium alloys used in bikes are chosen largely because they are weldable. Many Al alloys aren't.

A large number of Aluminium alloys gain there strength from precipitation hardening. These alloys are aged to give optimum precipitation size and distribution. Heating can lead to coarsening of the microstructure, where a small number of precipitates will grow at the expense of others leading to a fewer number of large precipitates. These ppts are characterised by incoherent interfaces with the matrix so now, rather than strengthening and toughening the alloy by there interaction with dislocations, the precipitates will embrittle the material, with the high energy incoherent interfaces acting as favourable crack nucleation and propagation sites.

It is this low ceiling to the operating temperature of these common alloys which lead to the development, at great expense, of 7000 series alloys for the aviation industry.

It just so happened that these and other similar alloys were ideal for bikes. However, for the majority of applications, it is not necessary to use an alloy which can be welded, if it doesn't need to be welded.

It is for this reason that I asked if axle happened to know which specific alloy the javelin was made from, so I could check it in my notes.

This is what I have been studying as my degree for the last three years.

8-ball