[A8] steel bolt in aluminum

[Rich, Jack]

I'm replacing my front axles, and the pinch bolt holding in the upper control arms was a bear to get out on the passenger side.  The drivers side is worse -- the head sheared off when I tried to spin it, and it cannot be hammered out at all.  I'm going to have to drill it out.  But I can't help but notice that the bolt is magnetic, i.e. some sort of steel, while the wheel bearing housing both looks like aluminum, and is non-magnetic.

Do I have the correct bolt installed?  Is it supposed to be steel?

Thanks,

Jack Rich