spark plugs

[Major Rant]

I would imagine the aluminium alloy is resistant to this precipitation heat treatment to a major degree, not daft these nips.

Its not an accidental thing done by daft people. Its an engineering thing done by engineers and accountants.
In this case they choose the cheapest aluminium that will do the job and I don't suppose they care what happens at the micron level at the extremes of temperature.
If Mr Gnasher says they can strip the threads if you try to shift stubborn plugs hot then I'd tend to believe him cos he's probably done hundreds and stripped 3.
I've got no evidence either way cos I've never had the problem cos I always put a small blob of grease (I use whatever's handy, usually LM3) on the plug threads before I screw them in.