The purpose of a frame should be prioritised in solving the popular dilemma. Top sprinters need to perform at speeds over 74 kmh or accelerate an over 100-kg load to 71-72 kmh in some 20 sec. So the frame should be stiff and light, no matter would it resist a houndred of events.
Amateur sprinters would need a frame to resist over time rather than to be so stiff and light. "Steel is real" is said and its Fatigue Strength of 370 mpa and Ultimate Tensile Strength (UTS) of 690 mpa remain unattainable by any alu alloy. Numbers:
Cold-drawn 4130 Cr-Mo Steel >
As for aluminium alloys utilized in framebuilding, I recently found too wide range of these. If mentioned, their four digits can only predict the presence of major alloing elements such as Mg or Zn. However, any mechanical property of given alu alloy, especially its Fatigue Strength, cannot be predicted by customers since the temper designation of this alloy is just absent.
-- 6061 > This anonimous material is likely most often mentioned in the frame specifications. It may be also named as "aluminum," "aluminum alloy" etc. Even in the most common T6 temper condition, its Fatigue Strength remains in the under 100-mpa range. I once broken up a cheap alu ahead stem adapter.
-- "Alumisonic aluminum" as stated by All-City, leads to Alumisonic Guitars where the alloys used include the 6061-T6 > aluminium.
-- 6066 > Utilised by Fuji, also mentioned by them as "A6-SL." No temper designation.
-- "Aluxx" as stated by Giant, is believed to be the very rare 6011 alloy. It may contain a tangible amount of Zn, up to 1.5 per cent, in contrast to another alloys of the 6000 series. Data on a couple of mechanical properties, just in the T8 temper condition, vere found in a sole source so far -- 6011-T8 > .
-- 7075 > Again with no temper designation, it is seen in the new Argon 18 Electron (27.2 seatpost, complete bike). The older frameset with aero seatpost was made from 3005 aluminium.
-- Columbus Airplane Alloy as stated by Cinelli. Ceeway.com > clarify the raw tubes to be 7005-T6 > After welding, a certain heat treating and artificial ageing process is suggested to restore the original strength.
In contrast to all that, the high-end Ambrosio Nemesis rim is clearly designated as "5086-h38" > that means the material used has 150 mpa Fatigue Strength.