aluminum vs. steel in brake disc
tractor trailer air (activated) brakes would be an extreme example of brake material application. The brakes are drum brakes made from cast iron, not aluminum.
Driving downhill for hours and using airbrakes consistently to keep the truck within speed limits, the brake drum gets red-hot temperature and can be seen glowing in the dark. That kind of temperature would melt aluminum. Also, the brake pads in any application would tear up the soft aluminum in just about any braking application.
The only way to cool down tractor trailer brakes is by waiting for an hour at a time.
If the brakes get too hot, they beginn to fail. That is then the last chance to pull over and let the brakes cool down.
So much for theory for truckdrivers. In practice, I was driving downhill for two hours and never had to worry about brake failure, using new equipment.
Taking about disc brakes, the physical laws are of course the same, and the application for cars is much lighter. But as far as I know, aluminum brake discs don't exist, it is still cast iron.
Anodizing is a protective layer of aluminum oxyde that protects the main body of aluminum from corrosion. There are several ways to anodize aluminum, and they probably use different words to describe different processes. We had 12 chemical tanks in a row, each about 2 yards wide, 20 feet long and 10 feet deep. The aluminum parts where in a large wire basket and travelled from tank to tank to be immersed for certain time periods. By skipping some tanks, each of which had different chemicals, one could anodize the parts either after one formula or another.
Heat treating changes the hardness of a material. The material can can brittle after hardening, so it needs to be softenened enough after hardening to be also tough. That process is called annealing.
Hardening is mainly done to iron or steel, working with the carbon in the steel, using heat. But there are other forms of hardening materials by alloying or even hammering the surface.
Just some basics.