6Al-4V Titanium Alloy, AMS 4911, Ti6Al4V, UNS R56400

6Al-4V Titanium Alloy, AMS 4911, Ti6Al4V, UNS R56400 i6Al4V, also known as grade 5, Ti-6Al-4V or Ti 6-4, is the most commonly used titanium alloy. It has a chemical composition of 6% aluminum, 4% vanadium, 0.25% (maximum) iron, 0.2% (maximum) oxygen, and the remainder titanium. It is significantly stronger than commercially pure titanium while having the same stiffness and thermal properties (excluding thermal conductivity, which is about 60% lower in Grade 5 Ti than in CP Ti). Among its many advantages, it is heat treatable. This grade is an excellent combination of strength, corrosion resistance, weld and fabric ability. This alpha-beta alloy is the workhorse alloy of the titanium industry. The alloy is fully heat treatable in section sizes up to 15mm and is used up to approximately 400°C (750°F). Over 70% of all alloy grades melted are a sub-grade of Ti6Al4V, its uses vary in many aerospace airframe and engine component uses and also major non-aerospace applications in the marine, offshore and power generation industries in particular. Generally, Ti-6Al-4V is used in applications up to 400 degrees Celsius. It has a density of roughly 4420 kg/m3, Young's modulus of 110 GPa, and tensile strength of 1000 Mpa. By comparison, annealed type 316 stainless steel has a density of 8000 kg/m3, modulus of 193 GPa, and tensile strength of only 570 Mpa. While tempered 6061 aluminum alloy has 2700 kg/m3, 69 GPa, and 310 MPa, respectively. Mill anneal 1300-1450°F 2 hours, air cool. Re-crystallization anneal bar for better ductility and fatigue strength, 1750°F 2 hours, furnace cool. For maximum fracture toughness and stress corrosion cracking resistance (SCC), Beta anneal 1950°F 1-2 hours, water quench. Then age 1150-1300°F 2 to 4 hours, air cool. For maximum strength, solution-treated and aged (STA) condition is: For sheet, 1675-1725°F 5 to 25 minutes, water quench. Age 975°F 4 to 6 hours, air cool. For bars and forgings, 1675-1725°F 1 hour, water quench. Age 975-1025°F 3 hours, air cool. For increased fracture toughness, but lower tensile strength, precipitation treat (overage) 1150-1250°F 4 hours, air cool. Stress relief annealing is commonly 1000-1200°F 1 to 4 hours, air cool. Ti 6Al-4V is susceptible to chloride (SCC), although being among the better of the titanium alloys in this regard. For marine environments silver plated bolts are not used, as silver bonds easily with chlorine in this environment. Ti 6Al-4V is also susceptible to SCC in environments such as methyl alcohol, red fuming HNO3, and N2O4. In the case of red fuming nitric acid, the problem is limited to environments containing less than 1.5% water, or more than 6% NO2. Failure in N2O4 has occurred when oxygen and chlorides were present as impurities. Ti-6Al-4V is the alloy most commonly used in wrought and cast forms. Palladium or ruthenium can be added for increased corrosion resistance. Most properties are affected by the microstructure, which is determined by the thermo-mechanical history. It is highly resistant to general corrosion in sea water. This alloy is available in most common product forms including billet, bar, wire, plate, and sheet. Ti-6Al-4V has Excellent biocompatibility, especially when direct contact with tissue or bone is required. Ti-6Al-4V's poor shear strength makes it undesirable for bone screws or plates. It also has poor surface wear properties and tends to seize when in sliding contact with itself and other metals. Surface treatments such as nitriding and oxidizing can improve the surface wear properties.