Loose connections - at the screw terminals - isn't the only or even dominant problem with AL wiring. Heat and conductivity is. Pure AL is a good conductor, and aluminum oxides are good insulators - aka dielectrics. Oxidization, and other chemical changes, can occur especially where there is contact of dissimilar metals (or materials for that matter). Even where the contact is AL to AL, the contact is not very good, because of the presence of oxides and oxidizers. Where the contact is between 2 metals and moisture is present electrolysis occurs and the "less noble" metal oxidizes at a compounded rate. Mildly put "aluminum ain't very noble". Air has plenty of Oxygen and moisture in it to support this entire process very nicely.
Incidentally, I've never seen pure, unoxidized AL, and I doubt that very many people have. That's because AL is an active enough metal that it's surface oxidizes almost instantly in any environment where oxygen is present. The oxidized layer is very thin, so that a highly reflective silver color can still be seen, but that initial thin layer is there. Just because it looks clean and shiny and pure doesn't actually mean that it is.
So, anyhow, with the oxides present, contact resistance is high. We're talking contact resistance as opposed to conductor resistance. With this resistance comes heat as power is applied and conducted. This additional heat accelerates and exacerbates the additional oxidization by corrosion and electrolysis. If the point is reached where the aluminum looks more white than reflective there is so much AL Oxide present that NO appreciable current would be conducted. Yes, THAT is how good a dielectric Alum Oxides are. And of course when that point was reached heat would again not be an issue, because not enough current would be conducted to even produce any significant heating.
In that middle phase, between virgin, perfectly pure AL with no oxides present, and insulator grade AL oxide is where the trouble lies. I don't know the typical condition of your wiring throughout the premises, but I'd bet that you could take apart ANY termination, flex the wire, and the insulation would crack. Aside from the physical absence of conductor insulation at the crack, you'd be looking at the irrefutable proof of the significant lasting presence of heat. Thermoplastic insulation has temperature ratings indicative of it's tolerance of heat, so that will indicate how warm those parts of the wire have been staying.
You can go to the aluminum wire marketing websites and literature and read all the "yeah-but"s as well as the methods and products developed to deal with these factors. For many large conductor applications AL is a good option, but small branch circuit wiring is not such an application. The AL industry doesn't even fight that anymore. Wire manufacturers will make AL wire if people will buy it.
There are still cheap, sleazy, stupid, pennywise/pound foolish people out there, some of whom could even be called electricians, that will install AL wire if it won't get caught by an inspector, or if the inspector can't or won't stop it's use. I can think of no legitimate use of AL conductors inside any building, with only a few exceptions in industrial occupancies. The "National Exception Catalog" notwithstanding.
