In my experience, chip welding (recutting) is the risk with deep slots in loominum. Pretty much all of the cutters I've broken over the last 2 years have been due to this. The best solution in my situation seems to be to ensure a constant supply of flood coolant, which both cools the chips down and clears the from the danger zone. I don't know if that would work for you, depends how much coolant you get get in there. Must admit, I do get a bit carried away with the feeds and speeds which probably doesn't help.

Using a smaller cutter and an adaptive path might at least reduce the chip size a bit and leave more room for chips and coolant to evacuate. If you are doing a 25mm deep slot with a 4-5mm cutter, you will be doing it in several (4-5?) stepdowns.

Dunno what others think?