We have had this discussion before. I am not a foundry person, but numerous metallurgy forums and sites talk of "creep" in Al alloys around 390F. And head specialists do softness test on car engine heads before they consider milling or guide work. Lots of scrap at these shops where new heads are required.
Yes and there is a lot of trash , misquotes and misconceptions that get posted , then reposted then reposted untill they become an undisputed fact, among those who do not know any better.
I can make you a batch of Aluminium that will creep under hot studio lamps or I can make you a batch that you can use to make rockets to propel grenades that are very stable almost up to their melting point of 865 deg C.
If you stop to think about it we make cast aluminium frying pans with electric elements cast into them and most of them run up to 400 deg C.
Although now days they just mark the thermostats 1 to 10.
Good chances your other half has an electric iron to iron your Y fronts.
Again an electric element cast into an aluminum shoe that runs up to around 200 deg C ( linnen setting ) and that surface is intended to remain perfectly flat.
Urban myths come from a fact, like head shops do Brinnels on heads before they do work on them if they think they have been overheated which is quite true.
Then they get applied to all sorts of things that are not applicable just because there is a similarity.
The alloys used for casting air cooled heads are different from the ones used for water cool car heads.
For starters they don't need and Mn or Mg to reduce water corrosion.
These alloys are differnt again to the ones used for marine heads as they don't need to be resistant to salt corrosion regardless of weather they are designed for an open ( salt water ) or closed ( fresh water ) cooling system.
in fact the alloy used for heads on all alloy engines is differnt to the ones used for alloy heads on iron blocks.
We have come a long way since the WWII days of LM -4 ( Light Metal number 4).
The piston inside the engine is also aluminum and according to your logic it should stretch an go to putty inside the engine.
It gets a lot lot lot lot hotter than a head ever will.
The thermal damage that happens to heads is very localised.
It happens around the exhaust valve guide .
This is because the exhaust valve runs at around 700 deg C ( bright red hot ) on a lawnmower and can go up to 900-1200 deg C on high performance car engines with long exhaust duration.
All of this heat has to be dissipated by the valve guide then transferred from the guide to the head
Exhaust valve metallurgy was the limiting factor to developement of higher performance engines again till WWII when research money for aircraft engines was endless.
I am not trying to make this a personnal attack on you but as an ex non- ferrous foundry metallurgist, I can not let misconceptions like this slip past as posts on this forum are searchable and will live a lot longer than you or I can ever hope to.
