I have a question about welding up holes. I have seen welders use a brass or bronze plate not sure which of the two it was as a backing plate when they were welding up holes. Could you use a pc of aluminum? Could you use a pc of steel with a brass shim covering it? I am just wondering what you can use for a backing plate if you want to weld holes up in another plate?
I keep a 2" by 2" section of copper electrical buss bar available for this. It works well as a backing for holes up to approximately 1" diameter, & does not fuse to the steel.
The brass shim you suggest, would not likely have sufficient mass & heat conductivity, to prevent it from melting to the steel backing.