ALUMINUM PIPE NIPPLES

https://www.pipenipples.com/aluminum-pipe-nipples/

Aluminum is an ultra-light metal, making it an optimal choice for low cost and lightweight pipe nipples. However, because they are vulnerable to corrosion, aluminum welded pipe nipple are not recommended for wet or salty environments.

Applications of Aluminum Threaded Pipe Fittings
Aluminum pipe fittings, a kind of threaded pipe fittings, are used only in specialty applications where their uses and limitations are understood. They are not designed for use in general shop water or air plumbing layouts (refer to traditional metals like brass, steel/malleable iron, stainless steel, plastics, etc. for general plumbing applications). Aluminum to aluminum pipe nipples and fittings are not designed to be removed or re-tightened as they will bind very quickly and easily (ie. the friction of threading together will cause the aluminum structural pipe fittings to bond to itself - PTFE sealants, pastes, or tapes can lessen the effect but will not prevent it). Therefore, once aluminum to aluminum threads are threaded together, it is considered permanent and the leak paths of the aluminum structural pipe fittings would be difficult to eliminate (but weld aluminum fittings are available, N205WD, N210WD, N225WD, etc).