It looks like it has been welded at some point and cracked when the weld has been hammered at a later date to split the joint. Without having it right in front of me, I am only offering an opinion.I can see the hammer mark, when I was serving my time my instructor would have made me sign that!
That crack will never progress to the ball joint mounting area, it is basically "flash" material above..if in doubt drill a small hole at the bottom of the crack/fill, that will stop it progressing, alternatively replace the part and go wash yer underwear....Mine looked exactly like that...Its not a weld, Id put money on it ! Its the casting seam that's been hammered by someone who is used to doing it that way before they realised it was made of aluminium...Or, maybe the stress crack appeared after the event...?There is infact very little parent material around the lip of the arm at this point.
Again, mine was cracked but not as badly, at least, initially. And you could see tha imprint from the hammer face - I left it as it wasnt 'progessed' enough (IMO) to affect the bulk of the material that the insert is pressed into; Didnt take long for it to become a problem though. The crack is effectively a stress notch. Accident waiting to happen...!?!>
I stand corrected , even Italian alloy appears to be a *****Yeah/no- it'll split right through.Top to bottom...opening like a yawning casm everytime you load the steering..
At least, Im pretty sure that must be whats happening given the amount of uncontrollable 'swerve' generated around the steering load..! Ask me how I know..