Overview Of Titanium Alloy Materials And Properties For Fasteners

Titanium alloy materials for fasteners are closely related to the manufacturing process and use of fasteners.
On the one hand, the manufacturing process of titanium alloy fasteners mainly includes three parts: 1. plastic deformation, such as top upsetting, reducing and rolling threads, etc.; 2. surface reinforcement, such as bolts load-bearing surface and the transition zone of the straight rod reinforcement, etc.; 3. machining, such as turning, milling and grinding, etc..
On the other hand, the fasteners are used for different purposes, the required material performance requirements are also different, which requires the use of different titanium alloy materials. Take rivets and bolts as an example, rivets need to be upsetting at one or both ends in the installation process, so the riveting process requires high plasticity of the material. Bolts generally require high strength, its strength level and 30CrMnSiA high-strength alloy steel is close to, so usually use high-strength titanium alloy materials.

Comprehensive the above two factors, fasteners with titanium alloy materials are also mainly divided into industrial pure titanium, (α + β) type and β-type titanium alloy three categories. Industrial pure titanium is mainly TA1 and TA2; (α + β) type titanium alloys, including TC4, TC6 and Ti-662, etc.; β-type titanium alloys to sub-stabilized β-type titanium alloys are mainly, this is because of sub-stabilized β-type titanium alloys, molybdenum equivalent generally in about 10%. Molybdenum equivalent less than 10% of the near β-type titanium alloys heat treatment strengthening effect is insufficient; molybdenum equivalent greater than 10% of the stabilized β-type titanium alloys in the aging heat treatment process, the β-phase stability will be higher, difficult to decompose, so sub-stabilized β-type titanium alloys the most obvious effect of the strengthening of the material. In addition, sub-stable β-type titanium alloy has excellent cold forming properties, can be cold heading, avoiding the use of professional heating equipment and gas protection medium, high production efficiency and material utilization, high dimensional accuracy of the formed fasteners, good surface quality. And (α+β)-type titanium alloy fasteners can only be formed by hot upsetting, which requires specialized heating equipment and gas medium, with low production efficiency and material utilization, and is also prone to the phenomenon of uneven heating temperature.
Rivets with pure titanium tensile strength of more than 350 MPa, shear strength of 240~350 MPa; (α + β) type titanium alloy rivets to annealed state, β-type titanium alloy in the solid solution state, and the two alloys of the tensile strength of the same, for the 800~950 MPa, the shear strength of more than 600 MPa. The titanium alloy materials for bolts are all sub-stabilized β-type titanium alloys except TC4 titanium alloy, and they are all used in the solid solution + aging state, except for the tensile strength of TB8, TB9 and Ti-555 alloys which can reach more than 1,200 MPa, and most of the β-type titanium alloys have tensile strengths of about 1,100 MPa, and the shear strengths of 650~700 MPa.