Space station

Can I send weapons for free to my Ally's using space station

If I know right , you can’t Because this is impossible as others can be used for single purposes, but you can send the same account as you want another.

You can transport weapons to a different world by use of cargo shuttles but such transports do not change the owner of the materials.
At the end, there must be a sell transaction to change the owner.

You can however place military units in a country of a federation member and support his war effort.