I’m doing an EV conversion where I’m making water blocks out of an aluminum billet and an aluminum sheet to water cool the battery packs.

Unfortunately, I’ve tried three different types of gasket makers : Permatex ultra black, ultra blue, and flexible. All of them failed under pressure after a few minutes. It’s only 5lbs of pressure, but for some reason it keeps failing, even when the sheet is still compressed onto the block.

Anyone know of a sealant that’s specifically for aluminum to aluminum bonding?

Is welding the only option here?