Corrosion Resistance Of Steel Sheets Research Articles

Effects of Si Addition on Interfacial Microstructure and Corrosion Resistance of Hot-Dip Zn–Al–Mg–Si Alloy-Coated Steel

Alloy coatings protect steel from corrosion in various applications. We investigated the effects of Si addition on the microstructure, electrochemical behavior, and corrosion resistance of steel sheets coated with a hot-dip Zn–Mg–Al–Si alloy using a batch-type galvanization process. Microstructural analysis revealed that the Zn–Al–Mg alloy coating layer contained a significant amount of Fe that diffused from the substrate, leading to delamination due to the formation of brittle Fe–Zn intermetallic compounds. However, the introduction of Si resulted in the formation of a stable Fe2Al3Si inhibition layer at the substrate–coating interface; this layer prevented interdiffusion of Fe as well as enhanced the coating adhesion. Additionally, the formation of acicular Mg2Si phases on the coating surface improved the surface roughness. As the Si content increased, the corrosion resistance of the coating improved. Specifically, the Zn–Al–Mg coating layer with 0.5 wt.% Si exhibited excellent anti-corrosion performance, without red rust formation on its surface even after 2600 h, during a salt spray test.

The effect of cerium pre-treatment on the corrosion resistance of steel sheets

The steel samples have been coated with cerium layer by cathodic electrolytic deposition from the Ce(NO3)3·6H2O solution in aqueous ethyleneglycol in the presence of hydrogen peroxide. The influence of the coating parameters (cathodic current density, pH, cerium concentration, hydrogen peroxide concentration, temperature, and treatment duration) on the surface properties; the optimum conditions of the formation of corrosion preventing coating have been elucidated. Hydrogen peroxide concentration and pH are the major factors influencing the deposition process. The corrosion resistance has been further enhanced after treatment with Na3PO4·12H2O solution. The cerium-coated samples have been subsequently coated by cathodic electrostatic deposition from the colloidal solution of the paint. The coated materials have been subjected to mechanical testing (hardness, impact, cross cut, bending, and cupping tests), and their structure has been visualized by electron microscopy. The cerium coating has been found to improve the steel corrosion resistance by 15%.

Aqueous dispersion of submicron-sized diamond particles for thermally conductive polyurethane coating

To improve corrosion resistance of steel sheet, polymeric resin coating has been practiced in steel industry. However, this method has a drawback to use because polymeric coating layer decreases the thermal conductivity. With an aim to enhance the thermal conductivity of the polymeric coating layer on steel sheet, submicron-sized diamond (μD) particles were employed as a thermally conductive material. Various anionic and non-ionic surfactants were tested in order to stabilize heavy μD particles in aqueous phase. Among them, 1-pyrenecarboxylic acid (PCA) endowed the best stability to μD particles. The polyurethane-based coating layer containing PCA-stabilized μD particles was applied on the steel sheet. The thermal conductivity of the coating layer effectively increased from 0.351W/(mK) (0wt% μD) to 0.434W/(mK) (for 1.0wt% μD). Furthermore, the corrosion behavior was not observed upon salt spray test for 144h.

Effect of Polyaniline Film by Electro-synthesis on Corrosion Resistance of Steel Sheets in the Aqueous Solution of Sodium Chloride

Increasing environmental concerns require to solve the problem produced due to the use of heavy metals in coating formulations. Therefore, it is necessary to develop new coating strategy employing inherently conducting polymers such as Polyaniline(PANI). Polyaniline films were electrosynthesized by oxidation of aniline on cold rolled and weathering sheets using the potentiostatic mode from an aqueous oxalic acid medium. Potentiodynamic polarization curves were obtained for cold rolled and weathering sheets in the aqueous solution of 3% sodium chloride. The structure and properties of polyaniline film were elucidated using SEM, DSC, SST. A high corrosion resistance of polyaniline films were observed with a gain of the corrosion potential around 600-900 mV positive in the substrate covered with polyaniline than in the case without it.

Vapour deposited Zn–Cr Alloy coatings for enhanced manufacturing and corrosion resistance of steel sheets

In the present work, various Zn–Cr alloy coatings were deposited on automobilistic steels by a vacuum process, in which Zn and Cr are evaporated from resistance heated sources. After ion etching, different Zn:Cr evaporation rates were applied to produce several compositions in the films until a final coating thickness of 4μm was obtained. The coatings were characterized with respect to morphology (SEM), structure (XRD) and hardness (by nanoindentation). The structure changed from the hexagonal Zn–Cr solid solution to a cubic (bcc) phase as the amount of Cr in the coating increased. Nanoindentation tests showed that the presence of Cr can significantly change coating hardness: this effect can be correlated with compositional and microstructural changes. To optimise the adhesion, the necessity of a multistage pre-treatment of the steel substrates was recognized. Further to Ar+ sputter cleaning of the substrates, the deposition of a thin Cr interlayer is necessary. It was observed that, without suitable pre-treatments, the coatings are poorly adherent.Salt spray corrosion tests revealed that even small Cr additions are able to significantly improve the corrosion resistance of Zn coatings. The time for red rust to appear is very long (at least four times) when compared to pure Zn vapour deposited, or steel sheet electroplated with Zn (reference specimens). The generation of protective corrosion products which can suppress cathodic reaction is considered an important factor for that improvement.

蒸着Ａｌ‐Ｃｒ合金めっき鋼板の耐食性

The corrosion resistance of steel sheets continuously vapor-deposited with Al-Cr alloy and the crystal structure of the deposited layer were studied. Furthermore, investigation of the electrochemical corrosion behavior and an analysis on the morphology and the state of the corrosion products were conducted. Al-Cr alloy deposited steel sheets with Cr content of about 10wt% had superior corrosion resistance and revealed about eight times higher corrosion resistance in salt spray environments when compared to steel sheets vapor-deposited with pure Al. Increase of the corrosion potential and the pitting potential and improvement in the corrosion resistance of the deposited layer itself were confirmed with an increase of Cr content. It is considered that the drastic decrease in the corrosion resistance of Al-Cr alloy deposited steel sheets with Cr content of over 10wt% is caused by the reduction of the galvanic protection of the deposited layer to the steel sheet. The corrosion products mainly consist of dense bayerite (β-Al(OH)3) and do not contain Cr compounds. The corrosion behavior was also discussed in connection with the crystal structure.

ポリエステル樹脂系接着剤を塗布したポリ塩化ビニル被覆鋼板の交流インピーダンス法による耐久性評価

A study was conducted on the durability of steel sheet coated with PVC using polyester adhesives that can be activated at a temperature of 180°C. Assuming a case in which the PVC becomes degraded and a corrosive electrolyte reaches the adhesive layer, the corrosion behavior of Zn-Co-Mo electroplated steel sheet coated with polyester adhesive only in 5%NaCl was studyed mainly by the AC impedance method. The film resistance (Rf) of polyester adhesives cured at 180°C was higher than that of conventional acrylic/epoxy adhesives, and the decrease in Rf and the increase in the capacitance (Cf) were smaller than those of conventional acrylic/epoxy adhesives in 5%NaCl immersion tests. It was found that there was good correlation between AC impedance measurement and corrosion resistance and adhesion. It is considered that the excellent corrosion resistance of steel sheet coated with polyester adhesives is due mainly to the addition of silane coupling agent to the polyester adhesives.

交流インピーダンス法によるポリ塩化ビニル被覆鋼板の耐食性に及ぼす下地鋼板の影響の測定

A study was conducted on the effect of base metals on the corrosion resistance of steel sheet coated with PVC using polyester adhesives. To examine the corrosion behavior at the adhesive/base metal interface, AC impedance measurements were made on steel sheets coated with adhesive only, when immersed in 5%NaCl. Base metals investigated were Zn and Zn-Co-Mo electroplated steel sheets and hot-dipped Zn, Zn-5%Al and Zn-55%Al plated steel sheets. The film resistance and corrosion resistance of the adhesives were affected by the plating of base metal, with Zn-Co-Mo plating showing superior corrosion resistance to Zn plating. In the cace of hot-dip plating, steel sheets plated with alloys containing Al showed excellent corrosion resistance. It was considered that the corrosion products, such as Co, Mo and Al compounds, under the adhesives affected the film resistance of adhesives measured by the AC impedance method and corrosion resistance.

Hydrolysis of trifunctional alkoxysilanes and corrosion resistance of steel sheets coated with alkoxysilane-derived films

Hydrolysis of trifunctional alkoxysilanes and corrosion resistance of steel sheets coated with alkoxysilane-derived films

Factors affecting the quality of hot-dip-galvanized steel sheets

The coating quality and corrosion resistance of steel sheets hot-dip galvanized by the conventional method in a semiautomatic plant were studied. The effect of various treatment processes such as surface pretreatment, dipping techniques and post-treatment processes on the coating quality, type and extent of defects was investigated. It was found that the coating quality was markedly influenced by the mode and the amount of zinc bath additives, in particular aluminium or antimony. The required amounts of such additives should be added at intervals in the form of binary zinc master alloys with a maximum aluminium or antimony content of 10%. The correlation of the bath temperature and the withdrawal speed with the sheet thickness is an important factor for quality improvement. The corrosion rate and electrochemical behaviour of sheets galvanized in a pure zinc bath and in baths containing various amounts of aluminium or antimony (0.02–0.1 wt.%) were examined in 1 N NaCl solution. Addition of aluminium or antimony slightly increases the corrosion resistance of the galvanized steel sheets. The corrosion resistance increases in the following order: pure zinc < ZnAl < ZnSb.