## 4 Results and Discussion
\(W_{\text{B1}}\), \(W_{\text{B2}}\), \(W_{\text{B3}}\), \(W_{\text{b1}}\), \(W_{\text{b2}}\), and \(W_{\text{b3}}\) denote the widths of the necking zone of the melt pool. \(W_{\text{D1}}\), \(W_{\text{D2}}\), \(W_{\text{D3}}\), \(W_{\text{d1}}\), \(W_{\text{d2}}\), and \(W_{\text{d3}}\) denote the widths of the lower surface of the melt pool. The simulation and experimental results are both typical \"nail\" shapes, and the appearance tends to be consistent. The experimental results of AH36 steel hybrid welding were compared with the simulation results to further verify the reliability of the simulation results. As shown in Figure 7, the magnitudes of the simulated and experimental melt pool widths for the three laser powers are similar, and the variation trend is consistent. The simulation results are slightly larger than the experimental results, which agrees with [PERSON] et al. [27]. With increasing laser power, the surface of the melt pool and the width of the necking zone increased at first, reaching a maximum value at 7.5 kW laser power. When the laser power was increased to 8 kW, the width of the upper surface of the melt pool and the necking zone shrank slightly. The width of the molten pool's bottom continued to grow as the laser power increased from 7 kW to 8 kW. As the laser power increased, the energy in the molten pool increased and the weld width increased. The workpiece collapsed as the laser power increased to 8 kW, some of the energy was transferred to the melt pool's bottom, the upper part of the melt pool's energy decreased, and the bottom collapse energy increased. The results in Figure 5 further demonstrate the reliability of the simulation results. Figure 6: Comparison of simulated cross-sectional profile and experimental cross-sectional profile: (**a**) laser power 7 kW, (**b**) laser power 7.5 kW, (**c**) laser power 8 kW. Figure 7: Simulation and experimental results of molten pool width. Figure 8a shows the total power share of the input laser power. Increasing the laser power increases its total power share. Figure 8b shows the total area share of the laser zone area. The laser area share of the lower part of the weld is smaller than the laser power share, indicating that some of the laser energy acts on the upper part of the weld to preheat the molten pool below the arc and increase the arc area. Under the same conditions of other process parameters, the laser area share gradually increased when the laser power was increased from 7 kW to 7.5 kW. When the laser power continued to increase to 8 kW, the laser zone area accounted for a smaller percentage, the laser power was too large, the bottom of the weld collapsed, and the melt pool energy moved down to the collapse, resulting in a reduction in laser area energy. With the arc parameters unchanged, changing the laser power can affect the energy distribution inside the hybrid melt pool. The energy density of the molten pool affects the temperature of the molten pool. Combined with the driving force equation, temperature affects the magnitude of the driving force. Therefore, it is necessary to study the energy distribution in the molten pool by analyzing the melt flow as well as the keyhole and depth variation of the melt pool [28]. Through this simulation, after 30 ms, the melt pool enters the stabilization phase, and the melt flow is in dynamic equilibrium within a certain range. Figure 9 shows the temperature and velocity at the line segment measured by selecting different positions of the line segment at 35 ms of simulation. The W\({}_{\text{A}}\) line is located at the maximum width of the molten pool surface, perpendicular to the welding direction; the D\({}_{\text{L}}\) line is located directly below the keyhole, along the depth of the molten pool.