## 3 Results and Discussion
### Effect of Temperature Distribution on Interfacial Bonding Process  
To clarify the effect of temperature distribution on the interfacial bonding process, the end face temperatures at different moments when the laser power was 600 W were extracted, and the corresponding temperature gradients were calculated using MATLAB, with the results shown in Table 2. For the interface with and without polymer filling, the temperature distributions in the aluminum alloy were similar, that is, the temperature at the center of  
Figure 8: Simulated temperature distributions and corresponding observed interfacial bonding process at 9.00 s when the laser power was 700 W.  
Figure 7: Simulated temperature distributions and corresponding observed interfacial bonding processes at different moments when the laser power was 600 W.  
the laser irradiation was the highest, a trailing appeared along the laser scanning direction, and the temperatures were uniformly distributed in the thickness direction. In contrast, the temperatures in the CFRTP composite and filled polymer showed a significant decrease along the thickness direction, and the filled polymer resulted in more temperature decreases. The maximum temperature gradient in the aluminum alloy was about 45 \({}^{\circ}\)C/mm, whereas that of the polymer layer was about 450 \({}^{\circ}\)C/mm and larger than that of the unfilled polymer of about 420 \({}^{\circ}\)C/mm. For the \(x\) and \(y\) direction temperature gradients, the \(y\) direction temperature gradient was consistent with the temperature gradient, while the \(x\) direction temperature gradient was related to the laser scanning direction. The \(x\) direction temperature gradient in the aluminum alloy was negative in the laser scanned area and positive in the unscanned area, when the laser scanned in the \(x-\)direction, with maximum and minimum temperature gradients occurring on the sides of the laser irradiation position. The \(x\) direction temperature gradients in the CFRTP composite and filled polymers were similar, with reduced positive and negative peak gradients and a trailing near the contact area with the aluminum alloy, which was mainly related to the heating hysteresis caused by the low thermal conductivity. When the interface was not filled with polymer, Figure 9 shows the interfacial bonding process between the CFRTP composite and the aluminum alloy at a laser power of 500 W. The laser scanning direction is from right to left, and the laser irradiated the surface of the aluminum alloy in the center of the observation area at 7.00 s. At this moment, a gap of about 60 \(\upmu\)m existed at the interface between the CFRTP composite and the aluminum alloy on the left side, while the gap on the right side was filled by the CFRTP composite. As the laser scanned to the left, the fibers in the CFRTP composite moved towards the \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Interface without Polymer Filling** & **Interface with Polymer Filling** \\ \hline \hline Temperature distribution & Laser scanning direction & Laser irradiation position & Laser scanning direction & Laser irradiation position \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Temperature distributions and gradients at the end face when the laser power was 600 W.  
aluminum alloy driven by the molten polymer matrix and filled the gap in the observed area by 7.19 s. Meanwhile, this also produced cracking between the matrix and fibers and formed the delamination between the first and second plies of the CFRTP composite. Similarly, the melting of the polymer matrix in the second ply was observed at 7.24 s, and the movement of the second ply towards the aluminum alloy eliminated the cracking in the first ply, but this likewise produced such defects in the second ply.