Alum ???

[bikenut]

Any chemical engineers out there...

Anyone used "alum" to eat away a steel screw sheared off in an aluminium hole ?

Anyone ?
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nuts about bikes

[stinkwheel]

I haven't but it does work. it needs to be strong alum and it needs to be hot and it takes a while.

You'd effectively need to be able to immerse the aluminium part in the stuff in a heated container like a cooking pan just off the boil. They use it a lot for extracting broken drill bits or taps from complex pneumatic valving.

Not going to be much use for say a snapped exhaust stud. While you could immerse the head in a big pan of the stuff, it would also eat the valve seats and any other permanantly affixed steel componants. It would do well at removing a seized in brake calliper bleed nipple or a sheared carb bolt once you have it fully stripped of all other non-aluminium componants.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[WD Forte]

This short video shows it working on a steel screw in brass
https://www.youtube.com/watch?v=JCADI0YSt8M
so we know it works
but as stinkers points out, there are practical issues to consider
plus time.
For exhaust studs etc I'd probably be looking at the
weld or drill/easy out/helicoil processes
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bikers smell of wee

[stinkwheel]

In other chemistry, you can dissolve brass out of aluminium using concentrated nitric acid. Has to be concentrated, not dilute. Good luck getting hold if it though and probably not really something to be trifled with.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.