Pulsed TIG Additive Repair of TB6 Titanium Alloy Microstructure and Property Optimization

Literature Overview

This study published in Materials Engineering (2024, Vol. 52, Issue 11, pp. 133-140) by Zhang Shuai and colleagues from Nanchang Hangkong University and Changhe Aircraft Industry Group addresses a critical challenge in aerospace manufacturing: the repair of TB6 titanium alloy components using pulsed TIG additive manufacturing technology. The research investigates how process parameters—specifically pulse current and pulse time—combined with post-weld heat treatment influence the microstructure evolution and mechanical properties of the repaired material. The work is supported by the National Natural Science Foundation of China (52205375) and multiple Jiangxi Provincial research programs, reflecting its significance in advancing domestic aerospace repair capabilities.

Core Technical Findings

The investigation established that at a pulse current of 50 A and pulse time of 40 ms, the as-repaired TB6 titanium alloy achieved a tensile strength of 1113 MPa with an elongation of 5.26%, representing the optimal baseline condition before heat treatment. The authors then systematically explored the effect of solution treatment temperatures (740°C, 760°C, and 780°C for 2 hours) followed by water quenching, and subsequent aging at three temperatures (500°C, 520°C, and 540°C for 8 hours).

Microstructure Evolution During Solution Treatment

As the solution treatment temperature increased from 740°C to 780°C, the primary alpha phase progressively dissolved while the beta phase grew and distributed more uniformly throughout the matrix. Water quenching suppressed further beta phase growth and promoted the precipitation of acicular orthorhombic martensitic alpha-double-prime phase within the beta grains. This transformation caused a decrease in tensile strength but a significant improvement in elongation, indicating enhanced ductility at the expense of strength.

Aging Response and Final Optimization

During aging treatment, the alpha-double-prime phase continuously grew and gradually transformed into equiaxed grains. The mechanical properties improved substantially with increasing aging temperature. The optimal condition was identified as 780°C/2h water quenching followed by 520°C/8h air cooling, yielding a tensile strength of 1119 MPa and elongation of 7.36%—a 37.8% improvement in ductility compared to the as-repaired state.

Process Parameters Summary

Parameter	Value	Effect
Pulse current	50 A	Optimal heat input for defect repair
Pulse time	40 ms	Controls arc stability and penetration
Solution temperature	740-780°C	Dissolves primary alpha, grows beta
Solution duration	2 h	Sufficient for phase equilibrium
Quenching medium	Water	Suppresses beta growth, forms alpha-double-prime
Aging temperature	500-540°C	Transforms alpha-double-prime to equiaxed alpha
Aging duration	8 h	Completes phase transformation
Final tensile strength	1119 MPa	Optimal condition
Final elongation	7.36%	Optimal condition

Engineering Practice Implications

The study demonstrates that pulsed TIG additive manufacturing can effectively restore the mechanical properties of TB6 titanium alloy components to levels comparable with or exceeding the base material. For aerospace engineers dealing with titanium alloy repair, several practical considerations emerge:

The pulse parameters must be carefully calibrated to avoid excessive dilution while ensuring complete defect fill.
The two-step heat treatment (solution plus aging) is essential to achieve the desired balance of strength and ductility; the as-repaired condition alone is insufficient for structural application.
The water quenching step introduces thermal stress that may cause distortion, requiring careful fixture design for complex geometries.
The 780°C solution temperature approaches the beta transus temperature of TB6, meaning precise temperature control is critical to avoid grain coarsening.

Key Questions and Reflections

The study raises an important question regarding the scalability of this repair approach for large aerospace components. While the laboratory-scale results are promising, the thermal gradient management during repair of thick-section TB6 components would be significantly more challenging. Additionally, the long aging time of 8 hours represents a productivity concern for high-volume repair operations. The authors should be commended for providing a clear process window, but future work should address residual stress measurement and fatigue performance of the repaired regions, as these are critical for aerospace qualification.

Study Insights

This research provides a systematic methodology for optimizing titanium alloy repair through the combination of additive manufacturing and thermomechanical treatment. The finding that alpha-double-prime phase transformation during aging can significantly improve ductility without substantial strength loss is particularly valuable for engineers designing repair strategies for safety-critical aerospace components. The approach validates the concept that additive repair, when properly followed by heat treatment, can restore full material capability—a principle directly transferable to other titanium alloy systems including Ti-6Al-4V and Ti-10V-2Fe-3Al.