Disassembling the front suspension components for axle cv boot replacement:

The pinch bolt (wheel bearing hub to upper control arms) got broken (despite days of penetrating oils soaking).

Does anybody know what material (alloy) is the bolt made from?
(Does not seem to be from steel).

Heating the housing did not help so far

Is the drilling the only option to get the bolt out?

 

Pinch bolts are steel.

Not sure about your specific model but some uprights are steel and some uprights are aluminum. Test with a magnet if you want to confirm how hot you can heat it.

Use a good quality penetrating fluid, for example WD-40 is not the one to use for this.

Keep heating, soaking and twisting the remaining portion of the bolt.

When replacing, recommend to use liberal amount of anti-sieze on new bolt.

 

This might be obvious but it wasn't to me: only part of that bolt is threaded, so turning it beyond a certain point doesn't do anything - you can drive it out the rest of the way. Check out a fresh new one to see what I mean.