Corrosion and protections of Somaloy® components

Abstract: Corrosion protection is very significant for metals in modern society from the view of industrial development. This thesis work project involves a research study that is aimed to investigate the effect of corrosion on the mechanical strength and magnetic properties of four no treated or treated Somaloy® component samples (Somaloy®700 1P,  Somaloy®700 3P, Somaloy®700HR 5P and Somaloy®110i 5P) provided by Höganäs AB and laminated steel sheets by salt spray test. The coatings for protection are phosphoric acid coating, sodium silicate coating, DCA-Modified silicone conformal coating and water-borne single coat paint respectively. Then the protective properties are evaluated by Electrochemical Impedance Spectroscopy (EIS) in 0.1 mol/L NaCl solution after 7 days exposure.   From transverse rupture strength (TRS) and hysteresis loop measurements by salt spray test, although the bar samples are treated coating, the corrosion decreases the mechanical strength to a certain extent more or less over time. For the magnetic properties, the corrosive environments hardly influence the magnetic parameters of the no treated or four types of coatings treated Somaloy® components. But the all kinds of magnetic parameters for laminated ring samples have a great variation after salt spray test.   In the EIS measurements, for the no treated samples, the initial corrosion resistance is only several hundred ohms and decreases after 1 hour, 8 hours and 1day exposure, then increases to a certain extent with time due to the corrosion products formed on the surface. For the sodium silicate coating, the initial corrosion resistance is approximately several ten thousands ohms and decreases rapidly only after 1 day exposure to several hundred ohms due to the sodium silicate film dissolves in the electrolyte solution and has no effective protective property. Then the following corrosion process is almost same as the no treated samples. For the water-borne single coat paint, the initial corrosion resistance can reach to several Giga-ohms and decreases over time, but can still stay at  level, indicating that this coating has a very good and effective protective properties.   EIS experiments indicate that water-borne single coat paint has a more effective protection than sodium silicate coating and can apply a better corrosion protection for the Somaloy® components   Key words: corrosion protection, soft magnetic composites, phosphoric acid coating, sodium silicate coating, DCA-Modified silicone conformal coating , water-borne single coat paint, salt spray test, TRS, hysteresis loop, EIS