I needed to tap 6 mm thread in the 2040 (you can also tap it in 2020)

What can possibly go wrong? Aluminum is soft, right? I have tapped a lot of thread in all kind of steel parts and have a steady hand.

Well, I broke a tap.

And then another one

From the other angle:

Oddly, I broke them not on the way in, but on the way out. I tried to be gentle, I did tried to turn it 1 turn in – half turn out, like with a hard steel. Nothing helped. At some point it just got stuck on the way out. I thought: I was able to screw it in, so it MUST go out. But try a notch harder and the tap breaks.

So what works? Look at this picture:

You need a quality tap (well, perhaps the broken ones were good too)
You need oil. Yes, oil for aluminum. You can cut aluminum without oil otherwise, but always tap aluminum with some oil!
You need a brush to remove aluminum from the tap.
And you need a lot of patience.
The tap gets stuck in aluminum on the way out even with oil, though not that hard. Don’t force it, instead turn it back in and then out a few times and eventually it will got released. Good luck!