What makes Ti-6Al-4V the most widely used titanium alloy?

Ti-6Al-4V (Grade 5) dominates aerospace titanium use due to: Balanced properties - Good strength (130-150 ksi UTS), excellent toughness, fatigue resistance; Versatility - Available in all product forms (sheet, plate, bar, forging, castings); Well-characterized - Extensive database, well-understood processing; Weldable - Can be fusion welded with proper procedures; and Temperature range - Useful to ~315C (~600F). Microstructure control: Alpha-beta alloy, heat treatment controls alpha/beta ratio; Mill-annealed - General purpose, moderate properties; Solution treated and aged (STA) - Higher strength; and Beta-annealed - Maximum toughness, lower strength. Applications: Engine components (compressor blades, discs to intermediate stages); Structural - Frames, fittings, composite interfaces; Fasteners - For composite structures; and Landing gear (replacing steel in some applications). Processing: Requires vacuum or inert atmosphere above ~450C, Machining difficult (low thermal conductivity, work hardening). Ti-6Al-4V represents 50%+ of titanium aerospace use.