A lot of modern street cars use aluminum suspension parts. Control arms, hubs, uprights. The engineers have figured that the fatigue life under street conditions is more than adequate.
The drawback is that they are physically larger.
Here is the suspension on the Nissan GTR.
Of course for a race car.. the aluminum would probably not be cast but something like hollow tubes welded to some ends or CNC. The disadvantages are the stiffness, so it buckles easier. warpage after welding etc. so the arms would need to be of more volume than a steel arm.
I was designing some control arms in Solid works for a small project. The steel arm had tubes 3/4" 0.065 steel. The aluminum arm is to be a CNC machined solid piece. The aluminum arm was roughly the same strength in the members and lighter by about 50% (I don't remember exactly but it was lighter by far).
The actual members of the arm were actually strong enough, but there was a problem. The ends of the arm that hold the bearings were failing. The small amount of material that surrounded the bearing was succumbing to stress concentration. The ends of the aluminum arm had to be enlarged as to not fail and so a bigger bearing had to be used to fill up the space. In the end, the total mass of the bearings and aluminum came within about 80% or 90% (memory not too clear)of the steel one and the upright had to be modified for this bigger part. So just to point out: sometimes because of other factors such as stress concentration at places were things are inserted and space constraints, It might be better off to choose strength over strength per density.
Still aluminum is a possible option.
