Corrosion Properties of Calcium Stearate-Based Hydrophobic Coatings on Anodized Magnesium Alloy

Abstract

A calcium stearate-based hydrophobic coating was formed on an anodized magnesium alloy by the electrodeposition method. The influences of the working voltages on the characteristics of the coatings were researched. The results indicate that the working voltages have significant effects on the morphology, thickness, roughness, and wettability of the hydrophobic coatings, but little influence on the phase composition. Higher working voltages promote the nucleation of the coatings during the deposition process. The thickness, roughness, and water contact angle of the coatings increase with the increase in working voltage. In addition, the influences of the working voltages on the corrosion properties and corrosion mechanisms of the coated magnesium alloys are discussed in detail. When the working voltage is 50 V, the best corrosion resistance is obtained, but when the working voltages are 20 V and 100 V, respectively, a low corrosion resistance is obtained because of the presence of the thinner and cracked coating on the substrate surfaces.

Polyvinyl butyral/3‐Hydroxy‐2‐naphthoic hydrazide/Poly (methylhydrosiloxane) Composite Coatings for Improved Stainless Steel Anticorrosion in Salt, Acid, and Alkali Solution

“…Wettability is one of the most important means to characterize the hydrophilic or hydrophobic properties of material surface, which is described by the spreading ability of water droplets on the solid surface [38,39] . The water contact angle (CA) and surface free energy (SFE) are significant standards to measure the spreading ability of water droplets of the coating, which have a great influence on its corrosion resistance.…”

“…As can be seen in the figure, different colors indicate different relative altitudes on the basis of the scaleplate on the right, the coating surface was relatively flat without large undulation with small amount of point bulge, which can form a layer of air cushion between the coating surface and water droplet, decrease the contact regions between solid-liquid, and improve the hydrophobicity of the coating. [13,39] Table 1 showed the results of surface roughness test of different coating samples, S a represented the surface arithmetic mean height which reduced from PVB coating (1.75 μm) to PVB/HNH/PMHS coating (0.46 μm), and S z represented the sum of the highest peak and the lowest valley of test area which decreased from PVB coating (18.73 μm) to PVB/ HNH/PMHS (14.58 μm). [33] In conclusion, the PVB/HNH/PMHS coating cut down the absorption of corrosive particles on metal surface notably and improved the corrosion resistance.…”

“…Wettability is one of the most important means to characterize the hydrophilic or hydrophobic properties of material surface, which is described by the spreading ability of water droplets on the solid surface. [38,39] The water contact angle (CA) and surface free energy (SFE) are significant standards to measure the spreading ability of water droplets of the coating, which have a great influence on its corrosion resistance. It can be conducted from Figure 5 (a) that different samples have different contact angle and surface free energy, when CA is greater than 90°, the coating is hydrophobic; when CA is less than 90°, the coating gets hydrophilic.…”

A Study on the Corrosion Resistance of Hydrophobic Coatings on 65Mn Steel

“…From the inset in Figure 3a, the protrusions are composed of nanoscale pore structures. By extending the electrodeposition time to 15 min (Figure 3b), cracks in the image become obvious (indicated with arrows), which might be caused by internal stress from the fast nucleation and growth rate of the coating [38]. The average size of protrusions increases to about 15 µm and some of them grow into honeycomb-like structures.…”

“…In summary, this work demonstrates a simple and effective pathway to prepare calcium stearate hydrophobic coatings, which improve the corrosion resistance of the 65Mn substrate. These coatings applied on the surface of magnesium alloys have been studied for use in the biomedical area [26,38], where they show superior corrosion resistance as well. However, 65Mn steel used for tools should have good mechanical stability, like friction and wear properties, adhesive strength, which shall be the focus of our future research.…”