Part 3: ICBMs and the cold war
Other than vehicles with a detached shock wave, all aircraft heat up more the faster they move. From the NASA book Facing the Heat Barrier: A History of Hypersonics :
At Mach 3 and higher, there was the Lockheed SR-71 that cruised at 85,000 feet. The atmosphere at such altitudes, three times higher than Mount Everest, has a pressure only one-fiftieth of that at sea level. Even so, this airplane experienced aerodynamic heating that brought temperatures above [260C] over most of its surface.
The SR-71 Blackbird gets to 260C over most of its surface. Aluminium anneals (softens) at 177C (alloys can be higher) making it unsuitable as a material for use on the outside of the Blackbird. The Blackbird used titanium instead.