Analysis of Surface Quality and Cold Heading Crack Control Technology for TC4 Titanium Alloy Bars

TC4 titanium alloy, with its excellent comprehensive mechanical properties at both room and elevated temperatures, has become one of the primary materials for critical aerospace structural components, including aircraft structural parts, aero-engine fan components, and drums. It accounts for more than 50% of the total titanium alloy consumption in the aerospace industry.

A large number of aerospace load-bearing structural components with variable cross-sections, as well as high-performance fasteners, require extremely high notch stress fracture resistance from raw material bars. These materials must possess excellent resistance to crack initiation and crack propagation, enabling effective prevention of structural fracture failure under high-stress concentration conditions.

During the cold heading forming process of titanium alloy fasteners, the surface roughness of raw titanium bars and the compression deformation ratio are the two key process parameters that directly determine cold heading quality, surface defect characteristics, and the reliability of final products.

Compared with hot forming processes, cold heading forming of titanium alloys offers significant advantages, including simplified processing procedures, high material utilization efficiency, effective work-hardening strengthening effects, and lower production costs. Its overall production efficiency and economic benefits are improved by approximately 1–2 times compared with traditional forging processes.

As a result, cold heading has become the mainstream forming method for aerospace titanium alloy bolts, rivets, and precision fasteners. However, the industry currently lacks unified evaluation criteria for defining surface micro-crack defects after titanium alloy cold heading forming. This results in insufficient systematic guidance for process parameter optimization, surface quality control, and forming stability management during production.

Therefore, an in-depth investigation into the relationship between TC4 titanium alloy bar surface roughness, compression ratio, and cold heading micro-cracks is of great significance for optimizing cold heading processes and improving the forming quality of aerospace fasteners.

This study takes annealed TC4 cold-drawn titanium alloy bars with different specifications as experimental materials. A systematic analysis was conducted on the microstructure, phase composition, and mechanical properties of the raw materials. Combined with optical microscopy, scanning electron microscopy (SEM) microstructural analysis, and finite element forming simulations, the study reconstructs the evolution of microstructure, stress distribution, and adiabatic shear band transformation characteristics throughout the cold deformation process of TC4 titanium alloy.

The influence mechanism of surface conditions and deformation parameters on cold heading defects was accurately analyzed.