CLADDING TECHNOLOGY SHANXI CO., LTDTA2 Titanium and 1060 Aluminium Dissimilar Metal Pulsed MIG Brazing
Literature Overview
This 2018 study published in the Journal of Heat Treatment of Metals investigates the pulsed MIG brazing of TA2 pure titanium to 1060 pure aluminium. The research was conducted by the Welding Research Center at North University of China in collaboration with the Beijing Aviation Manufacturing Engineering Research Institute of AVIC and the Experimental Center of Taiyuan Heavy Industry Rail Transit Equipment Co., Ltd. The work addresses a significant challenge in lightweight structural engineering: joining titanium and aluminium components without introducing excessive intermetallic compounds that would compromise mechanical and corrosion properties.
Core Technical Content
The joining of titanium to aluminium is inherently difficult because of the large difference in thermal conductivity, melting point, and chemical reactivity between the two metals. Titanium has a melting point of 1668 degrees Celsius while aluminium melts at 660 degrees Celsius, creating a wide processing window but also posing challenges for achieving proper wetting and bonding. The pulsed MIG brazing process was selected because it allows precise control of heat input through the pulse frequency, pulse duration, and average current, enabling the process to be tuned to minimize intermetallic formation while ensuring adequate joint strength.
Process Parameters and Microstructural Response
| Parameter | Value | Influence on Joint Quality |
|---|---|---|
| Pulse frequency | 100-200 Hz | Higher frequency reduces individual pulse energy, limits intermetallic growth |
| Pulse current | 180-250 A | Controls peak heat input per pulse |
| Background current | 60-100 A | Maintains arc stability between pulses |
| Wire feed speed | 3.5-5.5 m/min | Controls filler metal deposition rate |
| Travel speed | 0.3-0.6 m/min | Affects heat input per unit length |
| Filler metal | Al-12Si or Al-4.5Mn-0.5Mg | Al-Si filler reduces intermetallic thickness |
| Shielding gas | Pure argon | Essential to prevent titanium oxidation |
The microstructural analysis revealed that the intermetallic layers formed at the titanium-aluminium interface consisted primarily of TiAl3, TiAl2, and Ti2Al phases, arranged in a layered structure from the titanium side to the aluminium side. The total intermetallic layer thickness ranged from 15 to 45 micrometres depending on the process parameters, with the optimal combination producing layers below 25 micrometres. The Al-12Si filler metal was found to be particularly effective in limiting intermetallic growth because silicon acted as a diffusion barrier for titanium atoms migrating into the aluminium matrix.
Mechanical and Corrosion Performance
The tensile strength of the brazed joints ranged from 85 to 145 megapascals, with the highest values achieved at lower heat inputs and with Al-Si filler metal. The fracture mode analysis indicated that the majority of failures occurred within the intermetallic layer, confirming that the intermetallic region remained the weakest link in the joint. However, joints with intermetallic layers below 25 micrometres demonstrated fracture strengths exceeding 120 megapascals, which is adequate for many secondary structural applications in aerospace and rail transit.
Corrosion testing in 3.5 wt% NaCl solution revealed that the joint exhibited galvanic corrosion preferentially at the aluminium side, as expected from the galvanic series. The presence of the intermetallic layer provided some degree of galvanic isolation, but the effect was limited. The corrosion rate of the aluminium side was approximately 2-3 times higher than that of the base aluminium, while the titanium side showed minimal corrosion attack.
Standards and Engineering Practice Integration
This work has direct relevance to the fabrication of lightweight aerospace structures and rail transit components where titanium and aluminium are used in combination. The process aligns with the requirements of AWS D3.9 for aluminium welding and brazing, as well as the titanium welding standards in AWS A5.4 and ASTM B348. For rail transit applications, the findings are relevant to EN 12663 and TB/T 2340 standards for welded structures in rolling stock.
Defect Prevention and Process Optimization
The primary challenges identified include:
- Titanium oxidation leading to poor wetting and bond failure, mitigated by maintaining argon shielding flow above 20 litres per minute and using a back-purge for the titanium component.
- Excessive intermetallic layer thickness causing brittleness, controlled by limiting heat input through pulsed parameters and selecting appropriate filler alloys.
- Porosity from hydrogen absorption, reduced by thorough pre-cleaning of both base metals and using dry shielding gas.
- Cracking in the aluminium heat-affected zone, minimized by pre-heating the aluminium component to 100-150 degrees Celsius.
Study Insights and Engineering Implications
The research demonstrates that pulsed MIG brazing is a viable process for joining TA2 titanium to 1060 aluminium with acceptable mechanical and corrosion performance when process parameters are carefully optimized. The key insight is that the intermetallic layer thickness is the critical quality indicator, and it can be controlled to below 25 micrometres through appropriate selection of pulse parameters and filler metal composition. For engineering applications, this process offers a practical alternative to explosive cladding or roll-bonding for small-scale production of titanium-aluminium hybrid components. The work provides a valuable foundation for developing production-grade procedures for dissimilar metal joining in aerospace and rail transit manufacturing, where weight reduction is a primary design driver.