The material of the bar is irrelevant.  I have made many metallophones
using .224L, and it works perfectly.

One interesting fact is that in ancient times sand would be spread on
the bars to find the nodal points.  As the bar was struck repeatedly,
the sand would vibrate off except at the nodal points.  It is still
done that way today in primitive cultures.

Charlie Hind
http://www.hindocarina.com/