The technical difficulties of titanium alloy springs

(1) Material selection: Precisely matching requirements
Different application scenarios have varying requirements for the performance of titanium alloy springs, so it is necessary to precisely select the appropriate alloy material. TC4 (Ti-6Al-4V) has excellent comprehensive performance and moderate cost, making it suitable for most spring applications. TA18 (Ti-3Al-2.5V) has better high-temperature resistance and can be used in environments up to 450°C, such as engine valve springs. Pure titanium (TA1/TA2) has excellent plasticity but low strength, making it suitable for low-load springs, such as some situations where strength is not a high priority but good elasticity is required.

(2) Forming Process: Both Cold and Hot Present Challenges
Cold forming: Suitable for wire materials with a diameter of ≤ 6 mm, such as medical micro springs. However, titanium alloys undergo rapid cold work hardening, and during the cold forming process, intermediate annealing (at 700-800°C) is required to restore the material's plasticity. At the same time, the large amount of springback is one of the difficulties in cold forming, being 20%-30% higher than that of steel. To solve this problem, it is necessary to design the mold compensation or make multiple forming corrections to ensure that the size accuracy of the spring meets the requirements.

Hot forming: The temperature range is 750-900℃ (Ti-6Al-4V) or 700-850℃ (Ti-3Al-2.5V). During the hot forming process, inert gas protection is required to prevent material oxidation. The advantage of hot forming lies in the ability to process large-sized springs, such as aviation spiral springs, and to reduce residual stress, thereby improving the performance stability of the springs.

(3) Heat Treatment: Key to Optimizing Performance
Strain relief annealing: A heat treatment process of 1-2 hours at 500-650℃ can eliminate cold working stress, improve the dimensional stability of the spring, and reduce deformation during use.

Solution + Aging (applied only to α-β alloys such as Ti-6Al-4V)): First, perform solution treatment (quenching in water at 900-950℃), then conduct aging treatment (at 480-550℃ for 4-8 hours). This can increase the strength of the spring by 10%-15%, further enhancing its load-bearing capacity.

(4) Surface Treatment: Enhancing Performance and Lifespan
Shot peening treatment: By applying shot peening to the surface of the spring, a compressive stress layer is formed, with a depth of up to 0.1 - 0.2 mm. This effectively enhances the fatigue life of the spring and increases its ability to resist fatigue fracture.

Anodic oxidation: Forms a TiO₂ film (5-20 μm) which not only enhances the wear resistance of the spring but also improves its insulation property. It is suitable for some applications where both wear resistance and insulation are required.

(5) Welding and Connection: Ensure Structural Stability
Laser welding is commonly used for connecting the closed-end springs. During the welding process, it is necessary to strictly control the heat input to prevent the coarseening and embrittlement of the β phase, which would affect the performance of the springs. Precise welding techniques can ensure the structural stability and reliability of the springs.