ATI (formerly Allegheny Technologies) melts, rolls and forges the specialty metals that live inside a jet engine — nickel-based superalloys and titanium that must survive thousands of degrees and decades of thrust. It sits one step upstream of Boeing and Airbus: aerospace & defense is ~68% of its ~$4.6B revenue, led by materials for jet engines and airframes, so its fortunes track engine build-rates and titanium prices rather than the consumer economy.
One step upstream of the jet engine
ATI takes raw titanium, nickel and scrap, melts and forges them into superalloys and mill products, and ships them to engine makers (GE, Pratt, Rolls-Royce) and airframers (Boeing, Airbus). It never builds the engine — it makes the metal the engine can't run without.