. Steel is far more dense than aluminium, so for a given volume of material it is far stronger.
denisty does not necessarily correlate to strength
rough rule of thumb:
Ti 1/2 weigh of steel but appriox same strength
Al 1/3 weigh of steel but appriox 1/2 strength *
dunno what the number are for carbon fibre.
(* some alloys comp retty close to strngth of steel)
So there are weight saving to be made, but to make an alloy bolt smae stength as the steel one you are replacing would mean it has to be larger diameter, maybe M8 or M10..
anyways, my 3 rules of weighweenieing are:
1. can it be made lighter?
2. how much will it cost?
3. if it fails what are the consequences?
1. and 2 are knowns so with 3, you need to consider what will occur if the bolt on the braces give way. The forks should be designed that the bolts stop the stanchoins from dropping out so unless you get some big air, nothing bad is gonna happen, nebvertheless, I wouldn;t do it.
I am using alloy bolts for shifters, brake levers, gear wire clamps but not for holding disc brake rotors or anything that is safety critical like stem or seat post ....