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Netakure-
alloy bolts snapping in half when tightened
Bolts are not threads in a chainring. They usually fail from the combination of shear and tension at the conjunction of the thread and shank while being tightened. Chainring bolts are particularly vulnerable because they necessarily have a hole through the middle nearly as big as the root diameter of the thread.
It's clearly possible successfully to use 7075T6 chainring bolts, either with nuts or screwed directly into the chainring or the crank, but if anything is going to fail first it's most likely the bolt. This is in some ways a good thing, because it's the cheapest part to replace.
gbj_tester
Regardless of the grade of ali?
Just that I’ve dealt with several many seized and sheared ali chainring bolts but all that seems to go wrong with steel ones is rounding the allen wrench fitting. And I suppose occasionally they do get a bit rusty.
TLDR: I’ve had more hassle from aluminium than steel in this application so my anecdata says steel is better.