**4.4.4 Inhibited specimen with VL**

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 the alloy surface.

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

Improvement of Corrosion Resistance of Aluminium Alloy by Natural Products 393

The EDS spectrum proved the existence of carbon (due to the carbon atoms of the tapioca starch) and these molecules covered the surface of specimen. These data show that the

Fig. 14. EDS analysis of Al-Mg-Si alloy immersed in seawater containing 1000 ppm of TS

The corrosion inhibition studies of the aluminium alloy were carried out at room temperature using seawater and the results indicate that NH, VL and TS are an effective

The electrochemical studies of the corrosion inhibition process of Al-Mg-Si alloy in seawater using three selected natural products as corrosion inhibitors show that the corrosion rate of the alloy significantly reduced upon the addition of studied inhibitors. PP measurement reveals that the studied inhibitors can be classified as mixed-type inhibitors without changing the anodic and cathodic reaction mechanisms. The inhibitors inhibit both anodic

EIS measurements clarifying that the corrosion process is mainly charge-transfer controlled and no change in the corrosion mechanism occurred due to the inhibitor addition to seawater. It also indicates that the *R*ct values increase with addition of inhibitor whilst, the capacitance values decrease indicating the formation of a surface film. The EIS measurement also confirms the similar corrosion process and mechanism occurs in PP measurements. According to LPR data, the values of *R*p of Al-Mg-Si after addition of the studied inhibitors

corrosion inhibitor of aluminium alloy in that particular solution.

metal dissolution and also cathodic hydrogen evolution reactions.

increase with the following order: NH < VL < TS.

**5. Conclusions** 

carbonaceous material has covered the specimen surface (Figure 14).

The observations mentioned above were confirmed by EDS analysis (Figure 12). The EDS spectra showed an additional line characteristic for the existence of C (due to the carbon atoms of the VL). These data show that carbonaceous material has covered the specimen surface. This layer is absolutely due to the VL compound, because the carbon signal is absent on the specimen surface exposed to uninhibited seawater.

Fig. 12. EDS analysis of Al-Mg-Si alloy immersed in seawater containing 1000 ppm of VL.
