What material was/is used on the skin of the Blackbird SR71? What material was/is used on the skin of the Blackbird SR71 and how was it cooled.  How was it manufactured to be stronger with age
Titanium. Only the hottest portions of the fuselage (the chines) were cooled, using the fuel as a coolant. As far as I'm aware, there was no treatment to make the material stronger with age.