As slender as that whole part is, I'd guess it's steel.Emc209i wrote: I did a little googling and found that the w210 E430 uses the exact same knuckle as the E55. You could pick up a used set of knuckles cheaply and have them machined, given there's many more E430's in yards than AMG's.
Here's the left knuckle for a car without 4matic:
P/N: 2103300020
The oem parts appear gray like aluminum, so I figured the aftermarket stuff is Al with black paint. If it's steel that's even better for machining).
Aluminum's easier to machine, steel is easier to weld.