TIG Welding Process for Titanium Alloy Trusses in Unmanned Aerial Vehicles

Literature Overview

This research, published in Hot Working Technology (2026, Vol. 55, No. 12, pp. 104-113) by Song Hongsong et al. from the Beijing Research Institute of Aeronautical Materials and Aeroengine Youcai (Zhenjiang) Additive Manufacturing Co., Ltd., presents a systematic investigation of TIG welding processes for titanium alloy truss structures in unmanned aerial vehicle (UAV) applications. The study was funded by the Jiangsu Provincial Science and Technology Program (Grant No. BZ2024011). The research specifically addresses the heterogeneous welding of TC4 (Ti-6Al-4V) and TA18 (Ti-3Al-2.5V) titanium alloys, employing optical microscopy, scanning electron microscopy, and X-ray diffraction for microstructural and mechanical characterization.

Material Selection and Heterogeneous Welding Challenges

The selection of TC4 and TA18 for UAV truss structures reflects a deliberate engineering trade-off between strength and corrosion resistance. TC4 offers high specific strength suitable for load-bearing members, while TA18 provides superior corrosion resistance for components exposed to harsh environments. The heterogeneous nature of this joint introduces significant metallurgical challenges, including differential thermal expansion, microsegregation of alloying elements, and potential phase instability at the weld interface.

Welding Process Optimization

The authors identified optimal welding parameters of 30 A welding current and 10 L/min shielding gas flow rate for producing defect-free joints with uniform microhardness distribution. At these parameters, the weld joint strength exceeded 80% of the TA18 base material strength at both room temperature and elevated temperatures. The relatively low welding current is consistent with the thin-walled nature of UAV truss structures, where excessive heat input would cause distortion and microstructural degradation.

Microstructural Analysis

Microstructural examination revealed distinct zones within the weld joint. The weld metal exhibited a fine acicular alpha-beta microstructure, resulting from the rapid solidification cooling rates achievable with TIG welding at low current. The heat-affected zone in the TC4 side showed a Widmanstätten-type alpha structure with some beta phase retention, while the TA18 side exhibited a more equiaxed alpha microstructure with reduced beta phase. The transition zone between the two base metals displayed a gradient of microstructural features, with no brittle intermetallic phases detected by XRD analysis.

Distortion Control and Fixture Design

A significant contribution of this study is the development of specialized welding and heat treatment fixtures designed to control distortion in the truss structure. The fixture design incorporates strategic clamping points, welding sequence optimization, and controlled cooling provisions to minimize angular and linear distortion. The authors demonstrate that the fixture effectively suppresses welding distortion to acceptable levels, ensuring dimensional accuracy critical for UAV structural performance.

Welding Sequence Strategy

The welding sequence for the truss structure was optimized to minimize cumulative distortion. Symmetric welding patterns were employed to balance thermal input on both sides of the structure, and the sequence progressed from high-stress regions to low-stress regions to prevent stress concentration at partially welded joints. Post-weld heat treatment was integrated into the fixture design, allowing controlled cooling rates that promote microstructural homogeneity without introducing additional distortion.

Mechanical Performance Verification

The weld joints demonstrated satisfactory mechanical properties at both ambient and elevated temperatures. Room temperature tensile tests confirmed that the joint strength exceeded 80% of the TA18 base material, which is the weaker of the two base metals and therefore the controlling material for joint design. Elevated temperature testing verified that the joint maintains adequate strength under thermal cycling conditions representative of UAV operational environments. The uniform microhardness distribution across the weld joint indicates minimal segregation and good metallurgical compatibility between the two titanium alloys.

Study Insights and Engineering Implications

This research demonstrates that TIG welding is a viable and effective process for fabricating titanium alloy truss structures in UAV applications, even for heterogeneous joints involving different titanium alloy grades. The emphasis on fixture design for distortion control is particularly relevant for thin-walled aerospace structures where dimensional tolerances are stringent. The finding that low-current TIG welding (30 A) produces acceptable joints with uniform hardness suggests that heat input minimization is a primary design objective for titanium alloy welding in lightweight structures. Engineers working on similar applications should consider that the 80% strength criterion relative to the weaker base metal provides a conservative design basis, and that post-weld heat treatment can further optimize the mechanical properties of the joint.