if you are able to buy any such axle pieces for scrap metal price then just do it , ask for just an tiny piece or some chips first as an test sample and go to some large serious scrap yard and have it tested .
many of the larger scrap metal companies have very advanced testing equipment
they can tell you the exact alloy composition down to 1/100th of an percent .
then when you know what alloy it is you can check it up to see what its suitable for .
today there are so many odd alloys called bronze , there are even alloys without any tin at all called bronze .
but if the price is right you could always use it for an cannon with an steel sleve .
please just remember to hold the safety dimensions
minimum 1 caliber wall thickness at the breach
0,5 caliber at the muzzle .
thats the minimum .
