Aluminum is very common for service entrance and heavy feeders. The problems with branch circuits in houses wired with aluminum, was caused by incompatible components. The receptacles and switches were not designed for use with aluminum (there were no Co/ALr devices at the time) and anti corrosive paste was not used.
I used to own a house with aluminum wire. I bought it not knowing that, and my parents stopped over before I moved in and were looking around. Mom swore that she heard a sizzling in the wall of one room. After they left, I began pulling outlets and sure enough, I found a wire burned about a foot up from the receptacle. Wait, it get better.
This was a small house, about 900 sq/ft. built in two halves in a lumber yard, transported to the site, and set on the foundation, and bricked up. It was not a mobile home, double wide or anything like that. All regular stick construction. It was my first house also. The real estate agent had arranged for the "home inspector" to do what he had to do, and in the course of this, he determined that a couple of receptacles had the hot/neutral reversed. He would fix it if the owners wanted (they did) but would return later, as he was out of time and had to get going.
After I found the aluminum wire and the burned wire, I bought a case of CO/ALR outlets and a bottle of anti-corrosive paste and set about replacing all the outlets and buying myself some time. I found one other outlet with the wire burned. Strange however, was that the wire was burned and the side of the receptacle was not. Flipped it over, and the wire was OK, but the receptacle was burned!!!!!!! Apparently the inspector, not wanting to queer the deal, just swapped the wires and didn't tell anyone of the burned wires! Wait, it gets better!!!
The inspector, like a number of them in town, was a full time FIREMAN!!!! They work 7 days on, seven days off, so they all have second jobs doing home inspection, cable installing, etc.
I set about rewiring the house and when I sold it, I had about half of the circuits replaced with copper.
Charles