Galvanic inhibition mechanism

The inhibition mechanism of fluorides described above also operates on magnesium alloys in commercial coolants. For example, the inhibition effect of KF on the general corrosion of AM-SCl in MBL coolant at room temperature is illustrated in Fig. 11.10. The general corrosion rate of AM-SCl decreases as the concentration of KF increases. When the concentration of KF is greater than 1 wt%, the corrosion rate becomes lower than the corrosion rate threshold of 0.67 mg/cm /week [26]. However, for galvanic corrosion at high temperature, KF does not work very well in the MBL coolant. 

Motte, C., M. Poelman, M. Jourdier, D. Dispa, and M. G. Ohvier, Study of the inhibition mechanism of chrome free inhibitors on the galvanized steel corrosion by classical and local electrochemical techniques, Chimie Nouveau, 27, 2009, 1. 

The principle of this mechanism is based on the fact that conductive (p-doped) coatings could provide anodic galvanic protection to the metal substrate and act as an oxidizer to maintain the metal in the passive domain. This mechanism can lead to passivation of the exposed metal surface at small defects in the passive layer. A considerable number of reports have been made claiming the formation of passive films at the exposed site, with subsequent inhibition of further metal dissolution [129]. 

Ure2] Kirkaldy, J.S., Mechanism of Iron Attack Inhibition Arising from Additions of Aluminium to Liquid Zn (Fe) during Galvanizing at 450°C , Z. Metallkd., 64, 899-910 (1973) (Experimental, 26)... 

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