sonotrode material

hi chris, from ZVEI hanbook stated that only couples of type of material suitable to make sonorode such as titanium alloy, aluninium alloy etc..
my question is
1) if i want to fabricate a new sonotrode to replace for an existing sonotrode which being made by titanium alloy), is it possible i use other material for exam[le aluminium alloy ( as listed in handbook) to replace titanium alloy?

2) are we able to get the desire frequency and same size of sonotrode if we use different material i.e. titanium alloy compare to aluminium alloy?

regards
KL