**4.4.2 Unexposed specimen**

3322.3 [OH]

2931.3 [CH2, OH]

> Figure 7 corresponds to the SEM of the specimen surface after 60 days of immersion in seawater. Flakes showing corrosion products like metal hydroxides and its oxides can be observed, however no pits or cracks were noticed (Gao *et al*., 2008). The figures also show the presence of micro organisms (plankton) on the surface of the specimen which contributes to the corrosion process. The corrosion process in deep seawaters occurs under very specific conditions and is characterized mainly by high chloride contents, the presence of CO2 and H2S and micro organisms (Yagan *et al*., 2006).

Fig. 7. SEM of Al-Mg-Si alloy surface after 60 days of immersion

Improvement of Corrosion Resistance of Aluminium Alloy by Natural Products 391

The EDS spectrum in Figure 10 shows the existence of carbon (C), oxygen (O) and sulphur (S); due to the carbon, oxygen and sulphur atoms of the NH. These data show that carbonaceous material containing O and S atoms has covered the specimen surface. This layer is absolutely due to the inhibitor, because the carbon signal and the high contribution of the oxygen signal are absent on the specimen surface exposed to uninhibited seawater. It can be seen obviously from the spectra, the Al peaks are dramatically suppressed relative to the samples in uninhibited seawater (Figure 8). This is due to the overlying inhibitor film on

Fig. 10. EDS analysis of Al-Mg-Si alloy immersed in seawater containing 1000 ppm of NH.

Figure 11 portrays the SEM micrograph of Al-Mg-Si alloy immersed in seawater with the presence of 1000 ppm of VL. It was observed that compounds of VL were precipitated on

Fig. 11. SEM of specimen surface after immersion in seawater with presence of 1000 ppm VL

the specimen surface area (Amin *et al*., 2009).

**4.4.4 Inhibited specimen with VL** 

the alloy surface.

The EDS spectrum in Figure 8 presents the elements exist in Al-Mg-Si alloy after immersion test. It shows the presence of sodium (Na) and chlorine (Cl) in the specimen surface. Seawater predominantly consists about 3.5% of sodium chloride (NaCl) and many other ions. Chloride ions are very strong, and could easily penetrate the passive film, and dissolution of the aluminium substrate occurs and results in corrosion.

Fig. 8. EDS analysis of Al-Mg-Si alloy surface after 60 days of immersion.
