The density of titanium alloy is generally about 4.5g/cm3, which is only 60% of steel. The strength of pure titanium is close to that of ordinary steel. Some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloy is much greater than other metal structural materials, and parts and components with high unit strength, good rigidity and light weight can be produced. At present, titanium alloys are used in aircraft engine components, skeletons, skins, fasteners and landing gear.
Pure titanium is not heat-treatable. Generally speaking, almost no fasteners use pure titanium as a raw material. There are many titanium alloys, most of which are exclusively sold. Studies have shown that only a small portion of planed titanium alloys are suitable for manufacturing threaded fasteners. Ti-6Al-4V is a heavy-duty alloy. The minimum tensile strength of this titanium alloy fastener is 135,000 psi, which has high strength and satisfactory toughness. Ti-6Al-4Mn has great creep resistance and is easy to cast. Its strength characteristics are equivalent to Ti-6Al-4V alloy, but its toughness is slightly worse. The tensile strength of Ti-1Al-8V-5Fe is about 200,000 psi. To be exaggerated is its outstanding strength-to-mass ratio. The fastening force of fasteners made of this alloy is equivalent to that of steel fasteners of the same quality with a tensile strength of 350,000 psi. Two other titanium alloys-Ti-6Al-12Zr and Ti-6Al-6V-2Sn are sometimes used in the manufacture of fasteners.
The most attractive feature of titanium is its extremely high strength-to-mass ratio. Their quality is only 57% of the same volume of steel, but their strength is comparable to that of heat-treated iron-carbon alloys. Titanium is an ideal material for aerospace, jet aircraft and missiles. But its biggest disadvantage is the high cost. Unless there is no other choice, the use of titanium as a fastener material is discouraged.