..including crevices, regular plumbing flux and though I've had luck with most solders, 4% silver bearing solder is stronger Eventually...kinda high priced tho... I had Harris solder readily available at enough time so no massive deal for me but high priced if you do not have to have the energy https://foreign-auto-repair-near16034.blogprodesign.com/49202249/types-of-solder-to-use-on-aluminum-radiator-can-be-fun-for-anyone