SiO₂-Al₂O₃ sol gel coating solution was used for coating of mild steel substrate by dip coating technique with withdrawing speeds of 250, 500, 750 and 1000 mm/min. The coatings were subsequently heat treated at 200°C for 1 hour in order to improve their corrosion resistance properties. The coating sol was synthesised using Glycidoxypropyltrimethoxysilane (C₉H₂₀O₅Si) and Aluminium triisopropylate (C₉H₂₁O₃Al). The corrosion resistance of the both coated and uncoated samples was evaluated by the Tafel polarization in NaCl solution. Fourier transformed infrared (FTIR) and energy dispersive spectroscopy (EDS) analyses were used to identify the presence of various functional groups in the coating solution. A comparison of the corrosion resistance of the coated and uncoated mild steel is presented. Variation of corrosion potential (E_{corr}) has increased and corrosion current density (i_{corr}) has decreased in the coated samples. i_{corr} values of coated specimens, heat treated at 200°C, were 12 to 14 times smaller than those of uncoated specimen. The measured electrochemical parameters indicate that the corrosion resistance was improved by the coating.
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An investigation was carried out to examine the effect of austempering on the microstructure and mechanical properties of nodular cast iron GGG 50 (DIN EN 1563) alloyed with different amount of copper. Optical, scanning electron microscopy and energy dispersive spectroscopy analyses were performed for microstructural characterization. In addition, hardness and tensile tests were carried out for mechanical properties determination. Specimens were austenitized at 900°C for an hour, then austempered for an hour at 330°C in salt bath and cooled at a room temperature in air. The results indicated that the addition of Cu to GGG 50 encouraged pearlite formation in the matrix structure. In addition, with the austempering heat treatment, the structure was transformed from ferrite + pearlite into ausferrite and retain austenite. Furthermore, for the alloy with 2 wt% Cu addition, it was noted that the graphite nodules diverged from sphericity and Cu was concentrated around the graphite. After austempering, mechanical properties were significantly improved and the highest mechanical properties were found at 1.5 wt% Cu.
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