## 3 Research Findings and Discussion
### Four Point Bending Test  
In Figure 10a, the maximum shear force (~780 N) is seen in AZ91-AZ91 bolted-bonded samples and maximum displacement (~18 mm) in bolted samples. In displacement bolted-bonded samples, it has also a high value ratio of 17 mm. In Figure 10b, the maximum shear force (~1600 N) can be seen in CF-CF-bolted-bonded CF-CF-bolted samples, and the maximum displacement (~17 mm) can be seen in the same samples. In Figure 10c, the maximum shear force (~850 N) can be seen in AZ91-CF-bonded samples and the the maximum displacement (~17 mm) is in AZ91-CF-bolted-bonded samples. \begin{table}
\begin{tabular}{c c c c c} \hline  & **Maximum Tensile** & **Maximum Tensile** & **Maximum Tensile** & **Maximum Tensile** \\  & **Stress (MPa)** & **Tensile Force (N)** & **Elongation (\%)** & **Elongation (mm)** \\ \hline AZ91-AZ91-bonded & 30.31 & 4547.25 & 3.52 & 0.88 \\ \hline AZ91-AZ91-bolted & 32.19 & 4829.14 & 8.46 & 2.11 \\ \hline AZ91-AZ91-bolted-bonded & 34.68 & 5202.26 & 11.74 & 2.93 \\ \hline CF-CF-bonded & 34.49 & 5323.75 & 3.21 & 0.80 \\ \hline CF-CF-bolted & 35.11 & 5266.73 & 9.58 & 2.39 \\ \hline CF-CF-bolted-bonded & 37.84 & 5677.25 & 12.76 & 3.19 \\ \hline AZ91-CF-bonded & 34.41 & 5162.25 & 3.33 & 0.83 \\ \hline AZ91-CF-bolted & 34.69 & 5203.81 & 10.33 & 2.58 \\ \hline AZ91-CF-bolted-bonded & 38.57 & 5786.65 & 12.20 & 3.05 \\ \hline \end{tabular}
\end{table} 
Table 6: AZ91-AZ91, AZ91-carbon-fiber and carbon fiber-carbon fiber; tensile test values of bonded, bolted and bolted-bonded single lap plate joints. Figure 10: _Cont._  
In Figure 11a, the maximum shear force can be seen in CF-CF-bonded samples with \(\sim\)1200 N and the maximum displacement in samples AZ91-AZ91 is \(\sim\)16 mm. In Figure 11b, the maximum shear force can be seen in CF-CF-bolted samples with \(\sim\)1600 N and the maximum displacement is in AZ91-AZ91-bolted samples with \(\sim\)18 mm. In Figure 11c, it can also be seen that the maximum shear force is in CF-CF-bolted-bonded samples with \(\sim\)1600 N and the maximum displacement is in CF-CF-bolted-bonded samples with \(\sim\)18 mm. When the damage images as a result of the four-point bending test are examined in Figure 12, it can be seen that CF-CF bonded samples in Figure 12d and AZ91-CF bonded samples in Figure 12g the plates are separated from each other because the adhesive is broken, but in Figure 12a AZ91-AZ91 bonded samples did not break but they only bent like other bolted and bolted-bonded samples. This shows that bonded samples cannot carry the load and break. It can also be concluded that the adhesive has better adhesion in AZ91 samples than carbon fiber samples. The absence of peeling in the separated samples (Figure 12d,g) indicates that there is good adhesion at the adhesive and material interface. Table 7 shows the standard deviation values of single lap plate joints. Figure 11: _Cont._  
Figure 10: (**a**) AZ91-AZ91, (**b**) Carbon fiber-Carbon fiber and (**c**) AZ91- Four-point bending test force-displacement graph of carbon fiber bonded, bolted and bolted-bonded single lap plate joints. Figure 11: AZ91-AZ91, AZ91-carbon-fiber and carbon fiber-carbon fiber single-lap plate joints (**a**) bonded, (**b**) bolted and (**c**) bolted- bonded four-point bending test force-elongation graph. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**AZ91-AZ91-Bonded** & **AZ91-AZ91-Bolded** & **AZ91-AZ91-Bolded** & **CF-CF-Bonded** & **CF-CF-Bolted** & **CF-CF-Bolted** & **AZ91-CF-Bonded** & **AZ91-CF-Bolted** & **AZ91-CF-Bolted** \\ \hline
1.60 & 1.42 & 1.38 & 1.55 & 1.22 & 0.97 & 1.29 & 0.99 & 0.67 \\ \hline \end{tabular}
\end{table} 
Table 7: Bending test standard deviation values of AZ91-AZ91-carbon-fiber and carbon fiber-carbon fiber bonded, bolted and bolted-bonded single lap plate joints. Figure 12: _Cont._  
Various studies have been carried out to increase the mechanical properties of the AZ91 alloy. Aging after homogenization is one of the known processes of increasing its mechanical properties.