Steel producers use various organic and inorganic coatings to protect cold-rolled steel (CRS) sheets from corrosion during shipment and storage. It is well known that CRS sheets can be protected from corrosion by galvanizing, phosphating, chromating, topcoating with organic, or their combinations. The chromate rinsing is particularly effective for preventing white rusting of galvanized steel. But there is an increasing interest in a replacement for the chromating process because of environmental and health concerns. The objective of the present work is to develop a chrome-free conversion coating for steel sheets. Various carboxylic acids and their salts have been studied for coating phosphated electrogalvanized (EG) steel sheets, including 10-undecenoic acid (UA), oleic acid (OA), and other fatty acids such as stearic acid (SA) and palmitic acid (PA). When they were used alone, or subsequently coated with resin, they could produce a highly hydrophobic surface and improve the corrosion resistance. Thiols such as 1-octadecanethiol (ODT) can form a self-assembled monolayer on metal substrates. This close-packed monolayer could provide an excellent corrosion resistance for EG steel sheets. It was capable of withstanding 50~60 hours of salt spray test (SST) although its thickness was only a few nanometers. The EG steel itself usually started rusting only after 2~4 hours of salt spray. In another coating system, thiols were mixed with a conventional resin to improve the corrosion resistance of EG steel. This new technique gave 100~120 hours of corrosion resistance. When the resin was applied directly on EG steel surface, its corrosion resistance was less than 72 hours. It was shown that further optimization of this technique increased the corrosion resistance to 200 hours and more in the standard SST. / Ph. D.

The purpose of this research is to investigate the mechanical, microstructural and corrosion performance of the ferritic stainless steel coarse powders, used in Metal Injection Molding (MIM) process. Three coarser powders made by Höganäs AB, were examined along with a commercially available fine MIM powder and samples from sheet metal. The studied powders were individually mixed with binders and then injection molded in the shape of dog bone shaped tensile bars. These green samples were then debinded and sintered to examine under different characterization methods. The methods used for examining the samples were tensile test, hardness test, metallography, SEM, chemical analysis, and salt spray test. After a comparative study of these different materials, it turns out that the chemical composition and the process parameters have more effect on materials properties compared to only particle size distribution in studied materials. After this study, 434 coarse powder was preferred upon the PolyMIM 430 fine powder, because of its lower price and same performance as that of PolyMIM 430.

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

Influence of atmospheric and chemical environments on metal products leads usually to the corrosion damage. This master´s thesis deals with way to protect metals from corrosion, especially by polysiloxane coatings in combination with coatings containing zinc. Corrosion resistance of created coatings systems is tested by laboratory accelerated tests in corrosion chamber, where the natural atmospheric conditions are simulated. Chemical resistance in selected environments is verified by drop test. Quality characteristics coatings – thickness, adhesion to the underlying material, hardness and stability of the coating colour and gloss are evaluated too.

Organic coatings are extensively used as protective coatings in several industries including the automotive and aircraft industries. The last few years have witnessed an increased interest in improving not only the mechanical properties but also the corrosion protection properties of organic coatings. Among the currently investigated methods of improving the performance of organic coatings is the incorporation of additives in the organic paint matrix. Vapor grown carbon nanofibers (VGCNFs) are a class of carbon fibers that are produced by catalytic dehydrogenation of a hydrocarbon at high temperatures. Depending on the method of synthesis and the post-treatment processes, the diameter of the VGCNFs is normally in the 10-300 nm range. The small size, light weight, high aspect ratio, and unique physical, thermal, mechanical, and electrical properties of VGCNF make it an ideal reinforcing filler in polymer matrix nanocomposites to enhance the mechanical properties of the pure polymeric material in high performance applications in several industries such as the automotive, aircraft, battery, sensors, catalysis, electronics, and sports industries. The main objective of the current investigation was to study the corrosion protection offered by the incorporation of VGCNFs into a commercial alkyd paint matrix applied to the surface of mild steel coupons. The corrosion protection was investigated by immersing samples in air saturated 3% NaCl solution (artificial seawater). The samples were studied by electrochemical impedance spectroscopy (EIS) along with other measurements, including electrochemical (open circuit potential, cyclic voltammetry), chemical (salt spray test), electrical conductivity, and surface analysis (SEM, AFM, optical profilometry, and nanoindentation). The study involved the investigation of the effect of the weight percent (wt %) of the VGCNF as well as the coating film thickness on the corrosion protection performance of the coated steel samples when exposed to the corrosive electrolyte. By way of contrast, the EIS behavior of steel coupons coated with a paint coating incorporating different weight percents of powdered silicon carbide (SiC) particles was also studied. The EIS spectra were used to calculated and graph several corrosion parameters for the investigated systems. At the end, the studied coatings were ranked in order of their anticorrosive properties.