TC17 titanium alloy and Ti60 alloy each has its own unique advantages, the welding of the two can give full play to the advantages of their respective materials to improve the performance of the aircraft. This paper investigates the laser welding technology of 5mm thick TC17 and Ti60 dissimilar titanium alloys, and explores the microstructure of the welded joints, the characteristics of the porosity defects and their distribution, the tensile properties of the joints and the low-fatigue properties of the joints.
The TC17 titanium alloy is characterized by high strength and good hardenability, and is suitable for components such as low-pressure compressor disks of aero-engines; while the Ti60 alloy has excellent creep resistance and fatigue strength, and is suitable for use as high-pressure compressor disks of aero-engines and so on. Welding these two alloys can give full play to their advantages and improve the thrust-to-weight ratio of the aircraft. However, there are many challenges in welding dissimilar titanium alloys, so this paper carries out a study on laser welding of TC17/Ti60 dissimilar titanium alloys.
I. Experimental materials and methods
Experimental materials: 5mm thick TC17 and Ti60 titanium alloy test pieces were selected as the research object.
Material treatment: after cutting the test block, remove the surface stains with cleaning solution, then wipe with anhydrous ethanol and dry naturally.
Welding equipment and method: YLS-4000 fiber laser and YASKAWA welding robot were used for laser welding. Set the laser power, welding speed, laser defocusing amount and other parameters, and use the purity of 99.99% argon as a protective gas.
Second, the experimental results and analysis
Macroscopic morphology: the welded joint consists of three parts: the weld seam, the heat-affected zone and the base material, and the weld seam as a whole is X-shaped. There are more round metallurgical porosity defects in the lower part of the weld, and no porosity is found in the upper part.
Microstructure: The microstructure of TC17 titanium alloy base metal is β-phase + equiaxial α-phase, while Ti60 alloy base metal is dominated by equiaxial α-phase. The center of the weld consists of a large number of needle-like secondary α' phases, while the microstructure of the heat-affected zone undergoes obvious changes.
Porosity defects and their distribution characteristics: there are more porosity defects in the lower part of the weld, and these porosities may have an effect on the mechanical properties of the joint.
Tensile and low circumferential fatigue properties of the joints: tensile and low circumferential fatigue tests were carried out on the welded joints to evaluate their mechanical properties.
III. Conclusions and Prospects
In this paper, the laser welding study of 5mm thick TC17/Ti60 dissimilar titanium alloy reveals that the weld is overall X-shaped and there are more porosity defects in the lower part of the weld. Microstructure analysis showed that the center of the weld consisted of a large number of needle-like secondary α' phases, while the microstructure of the heat-affected zone changed significantly. The results of tensile and low-week fatigue tests showed that the mechanical properties of the welded joints were affected by weld porosity and microstructure. Further research will be conducted in the future to optimize the welding parameters and process methods to improve the mechanical properties and reliability of welded joints.
