Dear Pete:
I have the following data that may be usefull:
Alluminium: Transversal Wave Vel. (Vt) = 3,08 m/s
Longitudinal or Compressional W. V. (Vc) = 6,32 m/s
Al-Cu Alloy: Longitudinal Wave Vel.=3,10 m/s
Longitudinal or Compressional W. V.= 6,25 m/s
The following formulas can help you:
Vt= (E/(2p(1+u)))^(1/2)
Vc= (E(1-u)/(p(1+u)(1-2u)))^(1/2)
Where:
E is the Young Modulus (N/m2)
p is the material density (kp/mm2) (1kp/mm2= 0,98x10^7 N/mm2)
u is the Poisson's ratio (dimmensionless)
As you can see, the sound velocity depends of the material properties such as E, p and u, so I do not expect a big variation in the compressional wave velocity for different Alluminium Alloys.
I hope this help you.
Jorge Giraldo
MedellĂn, Colombia