**1. Introduction**

Titanium alloys exhibit high specific strength, excellent corrosion resistance and high thermal strength, which have been widely used in aerospace field to reduce weight [1–4]. In recent years, as the flight speed and distance of air vehicles increase significantly, traditional titanium alloys such as TC4, TA15 cannot cover the operating requirements. High-temperature titanium alloys possess excellent mechanical properties at high temperature, and the service temperature of these alloys is increased to above 873 K [5–7]. Due to these excellent performances, high-temperature titanium alloys have become advanced materials in aerospace applications, such as the components of aircraft engines, wings and rudders [8]. TC31 alloy is a high-temperature double-phase titanium alloy of the Ti-Al-Sn-Zr-Mo-Nb-W-Si system with high aluminum content, which can be used in a temperature range of 923–973 K [9–11]. This alloy also has good durability and creep properties under high load and high temperature [12]. Therefore, it has shown a prefect application in the aerospace field. To obtain a sound joint with good mechanical performance is a key factor to achieve structural integrity, light weight and low-cost manufacturing for its applications.

As an important part of laser manufacturing technology, laser welding is currently one of the most notable and most promising welding technologies. Due to its advantages of high quality, low deformation, high precision, high efficiency and high speed, laser welding technology has become a key joining method for airplanes and automobiles—with improved safety and structural weight reduction, clean and efficient shipbuilding—and nuclear power plant construction [13,14]. It is an effective way to achieve the upgrading of traditional industrial structures and achieve energy saving and emission reduction. Laser welding has been able to achieve the joining of many types of materials, and has many unmatched advantages of fusion welding processes [15–17]. For example, laser welding is used to weld aircraft skin and stringers [18,19]. Compared with riveted structure, the weight and cost of airplane is reduced dramatically. However, due to high degree of alloying and low plasticity-reserve for high-temperature titanium alloy, the possibility of cracking of the joint is higher than that of traditional titanium alloy, and it is easy to generate weld defects during welding [20–22]. The fewer the weld defects, the better the weld mechanical performances. In addition, the mechanical performances have a relationship with the laser welding parameters, such as laser power and welding speed, as verified by finite element method (FEM) and artificial neural network (ANN) simulation techniques [23–25]. Recently, laser oscillating welding has been promising in reducing the weld porosities and increasing the weld ductility [26]. However, most of the studies about laser oscillating welding purely focused on the mechanism of porosity suppression; there is a need for an exhaustive description of the relationship between the weld mechanical performances and the process parameters.

The paper gives the comparison of the weld profiles, microstructures and mechanical properties under different laser powers, welding speeds, laser beam weaving frequencies and amplitudes to obtain the sound welding parameters. In the study, high-temperature titanium alloy TC31 was welded by a laser oscillating welding method. The appearance, internal quality and microstructure of the weld under different welding parameters were observed. The mechanical properties of the joints at room temperature and high temperature were investigated. The mechanism for improved joint strength is also discussed.
