Fitted my 5.5mm Gamut Racering aluminium single ring chainring bolts that I was kindly sent free of charge from Madison.
When I removed my expensive Wolftoolth aluminium chainring bolts I totally cheesed one of them up, no idea why but in both sides of the bolt the hex keys just totally rounded out turning the bolt to cheese. Luckily I was still able to remove this last bolt but for a minute thought it was properly stuck.
Now I know how weak aluminium bolts can be I think I'll be sticking to ti or steel bolts in the future if needed.
They're aluminium and although I've not had any problems with these I wouldn't recommend buying aluminium chainring bolts, they can be expensive but you can get cheaper ones. I'd recommend titanium as the best material for chainring bolts that I've tried or even good old steel ones because aluminium is too soft and you can round out the hex slots far too easily.