Titanium alloy is a new important structural material used in the aerospace industry. Its specific gravity, strength and service temperature are between aluminum and steel, but it has high specific strength and excellent seawater corrosion resistance and ultra-low temperature performance. In 1950, the United States first used non-load-bearing components such as rear fuselage heat shields, wind deflectors, and tail covers on the F-84 fighter-bomber. Since the 1960s, the use of titanium alloys has shifted from the rear fuselage to the middle fuselage, partially replacing structural steel to manufacture important load-bearing components such as bulkheads, beams, and flap slide rails. The amount of titanium alloy used in military aircraft has increased rapidly, reaching 20% ​​to 25% of the weight of the aircraft structure. Since the 1970s, civil aircraft began to use titanium alloys in large quantities. For example, the amount of titanium used in Boeing 747 passenger aircraft reached more than 3,640 kilograms. Titanium for aircraft with Mach numbers less than 2.5 is mainly used to replace steel to reduce structural weight. Another example is the American SR-71 high-altitude high-speed reconnaissance aircraft (flying Mach 3 and flying height of 26,212 meters), where titanium accounts for 93% of the weight of the aircraft structure, and is known as an "all-titanium" aircraft. When the thrust-to-weight ratio of the aero-engine increases from 4 to 6 to 8 to 10, and the compressor outlet temperature increases from 200 to 300°C to 500 to 600°C, the original low-pressure compressor discs and blades made of aluminum must Switch to titanium alloys, or use titanium alloys instead of stainless steel for high-pressure compressor discs and blades to reduce structural weight. In the 1970s, the amount of titanium alloys used in aero-engines generally accounted for 20% to 30% of the total weight of the structure. Case, bearing housing, etc. Spacecraft mainly use the high specific strength, corrosion resistance and low temperature resistance of titanium alloys to manufacture various pressure vessels, fuel tanks, fasteners, instrument straps, frameworks and rocket casings. Artificial earth satellites, lunar modules, manned spacecraft and space shuttles also use titanium alloy sheet welding.