hmmmm....well the pic i posted of my control arms are steel, however the watts links i made out of aluminum tubing and aluminum jam nuts. The rod ends are steel. I made my control arms from steel because i figured they would take a lot of abuse. I figured the watts links didn't need to be indestructible, so i went with the lightweight option. Plus, the aluminum tubes have like .156" wall diameter compared to the steel around .09x"
I can tell you they held up fine when my wheel smacked into a curb, which resulted in the wheel being destroyed, the axle snapping at the wheel flange, the watts pivot point ripping off the bracket, and the whole 8.8 being pushed over about 3 inches. Aluminum watts links still fine. I guess only time will tell.