Here are pictures of solid-strand aluminum found during a recent inspection. The solid-strand aluminum was spliced into newer copper wiring using standard wire nuts which is the type of connection where aluminum can become a problem.
Solid-strand Aluminum branch wiring visible at the breaker AL and Copper joined together - this is a problem area
We inspect a lot of older homes and often find solid strand aluminum wiring for the branch wiring circuits. Clients often have lots of questions about aluminum wiring. Here is a link to an article that provides a good overview: