[Sequoyah101]

Steel screws in aluminum is a good recipe for sacrificial or cathode / anode corrosion. The aluminum is sacrificial to the steel and will oxidize to protect the steel from further corrosion. This may not turn out well.

Try the Kroil or liquid wrench or PB Blaster and gentle patience. It is likely the threads in the aluminum will come out with the screws though and you’ll have to drill and tap new threads or use a helicoil to keep the same thread size.

They have started using aluminum on some garden hose fittings. Given just a little time those suckers will weld in place with corrosion.

I just pulled some cap screws off the tractor this afternoon to find corrosion in steel or steel. Always assemble with thread lube if you expect to take things apart.

[Windflier]

Try the Kroil or liquid wrench or PB Blaster and gentle patience. It is likely the threads in the aluminum will come out with the screws though and you’ll have to drill and tap new threads or use a helicoil to keep the same thread size.

Thanks for the very informative reply. That's very helpful

I've already removed some zinc alloy bolts from the aluminum block, and they came out ok. I'm just crossing my fingers that some high quality penetrating oil and patience will do the trick for the steel machine screws, too.