The Influence of Process Parameters on Porosity in Laser-Arc Hybrid Welding

01 Introduction
Laser-arc hybrid welding technology combines the advantages of high energy density from laser welding and good gap-bridging capability from arc welding, making it highly valuable for welding medium-thick plates. In the welding process of medium-thick plates, due to the large material thickness, precise heat input control is required, and porosity defects are prone to occur. Porosity can significantly reduce the mechanical properties of the welded joint, affect weld compactness and corrosion resistance, and in severe cases, lead to structural failure. Therefore, studying the influence of laser-arc hybrid welding process parameters on porosity formation is of great significance for improving the welding quality of medium-thick plates.

Figure 1: Porosity defect morphology

02 Influence of Process Parameters on Porosity Defects
In hybrid welding, pores form when gases in the molten pool fail to escape before solidification and become trapped in the weld. Changes in laser power, welding speed, and welding current affect the amount of heat input, thereby influencing porosity formation.

Figure 2 shows the relationship between three process parameters—laser power, welding speed, and welding current—and porosity rate. It can be observed that porosity is directly proportional to laser power: as laser power increases, porosity increases. Porosity is inversely proportional to welding speed: as welding speed increases, porosity decreases. When welding current increases, porosity first decreases and then increases, reaching the minimum at 260 A.

Figure 2: Effect of different process parameters on porosity

Figure 3: Keyhole shape characteristics under different process parameters

Figure 3 illustrates the keyhole morphology under different laser power, welding speed, and welding current conditions. It can be seen that increasing laser power raises the frequency of keyhole collapse, which in turn increases sensitivity to porosity formation. When laser power is 2.6 kW, the keyhole tilt angle is small, and the keyhole walls are relatively straight, resulting in lower porosity. As welding speed increases, weld porosity decreases. When welding speed is 0.6 m/min, the keyhole is deep, the walls are curved and unstable. At 0.8 m/min, the keyhole is shallower, the walls are straighter, and the keyhole is more stable. At low speeds, keyhole stability is poor, increasing sensitivity to porosity. As welding current increases, heat input rises, and porosity decreases first, then increases. At 260 A, porosity is at its lowest; the keyhole tilt angle becomes smaller, and the opening at the top of the keyhole significantly enlarges. Meanwhile, as arc energy increases, the molten pool temperature rises, increasing keyhole opening size, avoiding necking phenomena, and enhancing keyhole stability.

Figure 4: Weld cross-sectional morphology under different process parameters

Figure 4 compares weld appearances before and after process optimization. After optimization, the number and size of porosity defects are effectively controlled, indicating that proper process parameters greatly reduce porosity formation. Higher laser power enhances keyhole penetration depth, but excessive power may cause violent keyhole fluctuations or collapse, trapping gas in the molten pool and increasing porosity. Conversely, low laser power results in insufficient penetration, failing to meet welding requirements. Higher welding speed accelerates molten pool solidification, but excessively fast speed impedes gas escape and may lead to keyhole collapse, trapping shielding gas in the weld and forming pores. However, excessively slow welding speed leads to high heat input, resulting in weld surface collapse and poor weld quality. Variations in welding current affect the width of the arc action zone. Increased current expands this zone, extending molten pool solidification time and aiding bubble escape. But if the current is too high, the excessive heat input can introduce shielding or ambient gas into the molten pool, increasing porosity.

03 Conclusion
In laser-arc hybrid welding, process parameters significantly influence porosity formation. Pores mainly result from keyhole instability, insufficient shielding gas flow, and surface oxidation. Their formation mechanism involves molten pool dynamics, gas escape, and solidification characteristics. Porosity defects notably reduce the mechanical properties and corrosion resistance of welded joints. Optimizing process parameters greatly reduces porosity formation and improves weld joint quality.

**--Cite the article published by 高能束加工技术 on February 17, 2025, in the WeChat public account "High-Energy Beam Processing Technology and Applications."