## 3 Results
### ATR-FTIR Analysis  
Figure 10 shows the ATR-FTIR spectra of a reference filler material Al alloy, Al composite materials, with all three concentrations, and binder system (functionalized PP; MAPP) in the range of 4000 and 500 cm\({}^{-1}\). The binder systems include MA grafted PP (MAPP), thermal stabiliser, and PP wax. The spectrum of the binder system showed characteristic peaks for polypropylene at 2950, 2917, 2868, 2842, 1456, 1374, and around 1018 cm\({}^{-1}\). Characteristic vibration at 2917 cm\({}^{-1}\) corresponds to CH\({}_{2}\) asymmetric stretching, the band at 2950 cm\({}^{-1}\) to CH\({}_{3}\) stretching, 2868 cm\({}^{-1}\) CH\({}_{2}\) asymmetric stretching. The characteristic peaks in the region at 1456 and 1374 cm\({}^{-1}\) were determined for CH\({}_{3}\) CH\({}_{2}\) rocking vibration. These peaks are in line with characteristic vibrations (symmetrical and asymmetrical) of hydrocarbon chains of PP, namely of CH\({}_{3}\) and CH\({}_{2}\) groups [64]. The spectrum of MAPP was investigated at wavelengths between 2000 and 1400 cm\({}^{-1}\). Three functional groups were present in MAPP. At 1778 cm\({}^{-1}\) a peak was associated with symmetric C = O stretching in cyclic anhydride. The characteristic peak at 1736 cm\({}^{-1}\) corresponded to the vibrations of ester groups (-C-O = O). In the 1240 cm\({}^{-1}\) region a characteristic vibration for C-O bond occurred. All three peaks suggest the functionalisation of PP with an anhydride, MAPP (maleic anhydride) [65]. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Material** & **Element** & **Atomic \%** & **Material** & **Element** & **Atomic \%** \\ \hline \multirow{8}{*}{AlSi10 Mg} & Oxygen & 43.24 & & Oxygen & 47.74 \\  & Carbon & 19.99 & & Carbon & 29.24 \\  & Aluminium & 19.96 & & Iron & 13.01 \\  & Silicon & 5.88 & & Manganese & 7.81 \\  & Magnesium & 10.57 & & Silicon & 4.24 \\  & Zinc & 0.34 & & Chromium & 2.19 \\  & Oxygen & 47.84 & & Oxygen & 55.97 \\  & Carbon & 29.86 & & Silicon & 26.08 \\  & Titanium & 15.79 & & & Boron & 8.78 \\  & Aluminium & 6.68 & & Sodium & 3.62 \\  & Vanadium & \textless{}0.5 & & Carbon & 3.47 \\  & & & & Aluminium & 2.08 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Elemental composition of the surface of the fillers measured by XPS. The aluminium materials usually show vibration peaks from 800 to 200 cm\({}^{-1}\). The ATR spectrum of Al filler (AlSi10 Mg) indicated an oxidation process on the surface. The peak at 1073 cm\({}^{-1}\), can be associated with Al-O vibrations, the peak at 900 cm\({}^{-1}\) can be related to OH vibrations and peak at 588 cm\({}^{-1}\) to Al-O vibrations. ATR spectra of Al composite materials (Al_30, Al_45, and Al_60) showed the characteristic peaks for PP, with the majority belonging to the \(-\)CH\({}_{2}\), \(-\)CH\({}_{3}\) groups of the aliphatic chain of the composites. In further analysis, we focused on the characteristic peaks for PP functionalised with maleic acid, between 1400 and 1800 cm\({}^{-1}\) wavelengths. It was observed that the vibration peak at 1778 cm\({}^{-1}\), related to cyclic anhydride PP disappeared and the vibration peak of MAPP at 1736 cm\({}^{-1}\) decreased. It is reasonable to assume that the MA anhydride PP ring opened and reacted with the Al filler. Additionally, a peak shift from 1073 to 1040 cm\({}^{-1}\) (associated with Al-O-H vibrations of filler) was observed, which indicates the binding of Al-O surface group located on Al filler material to the binder system and formation of a covalent bond between Al filler and MAPP. The same changes were observed regardless of the filler concentration. The main mechanism of chemical bonding between Al alloy and functionalised MAPP is shown in the lower right corner of Figure 10.  
Figure 11 shows the characteristic vibrations of the binder system (functionalised PP-MAPP), 316L composite materials at all three concentrations and as a reference, the spectrum of 316L filler material. As expected, typical vibrations peaks of PP, MAPP, and thermal stabiliser, were detected.