Aluminum has an interesting property: spalling.
From Wikipedia: "...Spall are flakes of a material that are broken off a larger solid body and can be produced by a variety of mechanisms, including as a result of projectile impact, corrosion, weathering, cavitation, or excessive rolling pressure (as in a ball bearing)...."
I know that many alloys of aluminum, when under pressure, in contact with harder materials such as steel or harder alloys of Al, and as a result of contact motion under these circumstances, will exhibit spalling. This is usually referred to as a "defect" and must be accommodated in mechanical machine design.
Perhaps this may be considered a benefit in the design of a metal bow. Spalling may serve to hold rosin. A different rosin characteristic may be required. Empirical testing seems to be the quickest avenue to exploitation of this idea. I fear there are other difficulties.
One is the 'hair' aspect. Would any alloy of Al be of sufficient mechanical strength to last for any time in a diameter close to horsehair? I think maybe not but it has been a while since I have toyed with such design ideas.
Technique requires the 'bounce' and 'feel' provided by the physical characteristics of conventional bows (tension, for instance). Therefore, an hybrid mechanical 'alloy,' possibly with another metal such as steel or copper; or in composite (possibly, embedded) with(in) a suitable polymer might be investigated.
One thin, flat ribbon of Al alloy comes to mind, as proof of concept. Two, or several flat ribbons set at an angle would allow flexibility.
Other metals such as Cu, Zn, Sn, etc. may yield better results...
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