## 1 Introduction  
With the rapid development of industries and technologies, the demand for electricity continues to expand [1]. Currently, burning fossil fuels is still the main method of generating electricity for civil use, resulting in environmental pollution and the greenhouse effect [2]. Therefore, the development of clean energy resources, including hydro power, plays an important role in satisfying the needs of social industries and protecting the global environment. Metal bellows are a key and elastic component of a hydro power plant, designed to accommodate the movement, vibration and thermal expansion of hydro power components [3, 4]. According to their structure, bellows fall into two groups: one-layer bellows and multi-layer bellows. [PERSON] et al. [5] reported that a lower forming residual stress could be obtained by applying multi-layer bellows, in comparison to one-layer bellows. This is attributed to the narrower plastic strain region of multi-layer bellows during forming. [PERSON] et al. [6] studied the deformation behaviors of four-layered bellows, and found that the differences in equivalent stresses among the four layers were neglectable in hydroforming. [PERSON] et al. [7] proposed that the design of metal bellows should be reasonable, considering the effect of residual stresses. Thus, metal multi-layer bellows are widely used in hydro plants. In industrial applications, the joints between metal bellows and other components are the weakest link in hydro power plants because they accommodate stresses and dis placement within the system. Gas tungsten arc welding (GTAW) and gas metal arc welding (GMAW) are often applied to join them [8, 9, 10, 11]. Due to their special multi-layer structures, the interlayers of multi-layer bellows before the arc welding processes are difficult to clean fully, leading to the formation of pores [12, 13]. Moreover, during multi-layer and multi-pass welding processes, the strong plastic deformation of multi-layer bellows, which is caused by heat accumulation and enlarged interlayer distances and is prone to the defect of insufficient fusion [14, 15]. [PERSON] et al. [16, 17] predicted residual stresses in joints fabricated by arc welding, and found that both a moving heat source and thermal cycles are important in the prediction of the residual stresses of welding. [PERSON] et al. [18] studied the tensile properties of GTAW joints and found that the fracture site occurred in the heat-affected zone (HAZ) of 316L stainless steel parts, which is related to the effect of large plastic deformation in the soft HAZ and the function of stress concentration induced by the presence of the sigma (\(\sigma\)) phase. [PERSON] et al. [19] investigated the susceptibility to stress corrosion cracking of 316L stainless steel joints, and micro-cracks were observed in the soft HAZ owing to the increased susceptibility to pit initiation. In conclusion, reducing the soft region in joints and avoiding the presence of the \(\sigma\) phase are necessary in terms of obtaining good weld joints. Different from conventional arc welding methods, precise laser welding has the ability to improve welding properties by manipulating the weld interface carefully [20, 21, 22, 23]. In addition, laser welding methods often have a narrow HAZ and defect-free weld seams due to their high energy density and low heat input [24, 25, 26, 27, 28]. [PERSON] et al. [29] used different welding methods to join stainless steel plates, and the results showed that the bead width was 11 mm in arc welding and 2 mm in laser welding, respectively. Therefore, the laser welding method has the potential to join multi-layer bellows and other components together in a high-quality manner. In this work, the process experiments of GTAW and laser welding with filler wire were carried out to weld dissimilar metals: multi-layer 316L austenitic stainless-steel sheets and one-layer high-strength steel plate. Firstly, the effects of the two welding processes on weld formation were studied via experimental processes.