Welding aluminum... Yes, it can be done, but usually requires a post-weld heat treatment (depending on particular alloy). Basically, though, you're just kicking the can down the road a bit, and it's going to fail again soon.

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welding aluminium is often a PITA, first off, if you dont know what grade, then could have a hard time matching the filler material (and some grades cant be welded at least not reliably). also cast parts often have impurities in the metal that make them dificult to weld.

apart from all that, as soon as you weld that the heat will travel up to the carbon joint, so you'd need to remove it from the carbon frame to weld, in which case it would be best just to replace the part if available from QR, or get one from a scrap frame.

Agreed, new bike time.

I had my Crack and Fail do what it says on the tin, and not replaced under warranty - news to me and the bike shop that the minimum extension line had to be not in line with the top of the seat tube, but visible through the slot in the seat tube - long story short, horrible to deal with, only got a discount on a new bike that would fail anyway... had it rewelded by a guy who does rewelding for trials motorbikes and suchlike, still cracked again.

Perfect excuse for a new frame or new bike.