How To Prevent Cracks in Titanium Alloy Welding?

Titanium alloy has become a key material in high-end fields such as aerospace, marine engineering, and medical devices due to its excellent specific strength, corrosion resistance, and biocompatibility. However, during the welding process, titanium alloy has potential risks of crack defects. This problem affects the mechanical properties and service safety of components, restricting its wide application in complex structure manufacturing scenarios.

 

 

The physical and chemical properties of titanium alloy determine the particularity of its welding process. The occurrence of cracking is the result of the combined effect of the material's own properties and welding process factors. Hot cracks are intergranular failures at high temperatures; cold cracks are the core threat of hydrogen-induced cracking; reheat cracks are hidden dangers during aging treatment.

 

 

In response to the mechanisms of welding cracks in titanium alloys, crack prevention technology must run through the entire process of "pre-welding preparation - welding process - post-welding treatment".

 

(I) Pre-welding Preparation

The core of pre-welding preparation is to reduce the introduction of impurities and stress concentration, and create stable conditions for the welding process.

• Selection of Base Metal and Filler Material: Choose filler wires with matching compositions. For high-strength titanium alloys, boron and zirconium can be added to refine grains; grind/pickle to remove oxide scales, oil stains and other impurities on the surface of base metal and filler wires, and complete welding within 4 hours after treatment.

 

• Joint Design and Groove Processing: Prefer butt joints with a groove angle, root face, and gap ; use cold working methods like milling for groove processing, and thermal cutting is prohibited.

 

• Welding Environment Control: Operate in a closed workshop with specific temperature and humidity; for important components, set up protective sheds and use dehumidification and dust-proof equipment to prevent moisture and dust from entering the molten pool.

 

(II) Welding Process

The welding process is the core link of crack prevention. It is necessary to achieve precise control of the molten pool and heat-affected zone through the selection of welding methods, optimization of process parameters and enhancement of protection.

 

• Preferred Welding Methods: Prioritize methods with concentrated energy and controllable heat input. Use TIG welding for thin plates (≤10mm) and PAW welding for medium and thick plates; for high-end fields such as aerospace, EBW and LBW welding are preferred (excellent but high cost), and manual arc welding is strictly prohibited.

 

 

• Optimization of Process Parameters: The core is to control heat input and cooling rate. Current: 50-80A for thin plates, 100-150A for medium and thick plates; voltage: 10-15V; speed: 5-10mm/s; interpass temperature for multi-layer welding ≤100℃.

 

• Enhanced Protection Measures: Use high-flow pure argon with purity ≥99.99%, equipped with a trailing shield (to keep the weld seam cool below 400℃) and back protection (argon back blowing; for pipeline welding, fill the pipe with argon before welding until the oxygen content <0.01%). It is normal to observe the molten pool showing silvery white; stop welding for treatment if it is blue-purple.

 

(III) Post-welding Treatment

Post-welding treatment can eliminate residual stress and reduce hydrogen content, thereby preventing cold cracks and reheat cracks. The core processes are as follows:

 

1. Post-welding Dehydrogenation Treatment

Applicable to titanium alloy components prone to cold cracking, implement immediately after welding: hold at 200–250℃ for 2–4h to promote hydrogen diffusion and precipitation, and inhibit cold cracking.

 

2. Stress Relief Annealing

Process: hold at 550–650℃ for 1–2h, cool with the furnace to below 300℃ and then air cool. It can eliminate more than 80% of residual stress, refine the microstructure and improve mechanical properties.

For age-hardening titanium alloys, annealing + aging should be used in combination to avoid reheat cracks.

 

3. Weld Seam Surface Treatment and Inspection

Grind to remove weld beads, spatter and oxide scales, and check for surface cracks;

Use ultrasonic testing (UT, sensitivity ≥Φ2mm flat-bottomed hole equivalent) and penetrant testing (PT, no linear defects) to detect internal/surface defects;

Cracks must be removed by mechanical grinding, and re-welding according to the original process and re-inspection are required if necessary.

 

 

Except technical measures, a sound quality control system is the key to crack prevention.

 

• Welding Procedure Specification (WPS)

Conduct process tests for different titanium alloy grades (Gr2, Gr5) and joint forms to determine the optimal parameters; construction without evaluation is strictly prohibited.

 

• Welder Management

Welders must hold special qualifications for titanium alloy welding and be familiar with the particularities and crack prevention requirements of titanium alloy welding.

 

• Whole-process Traceability

Record the batches of base metal and filler wire, welding parameters, post-welding treatment and flaw detection results throughout the process to achieve accurate traceability of problems.