Papers by Keyword: Hot-Dip Galvanizing

Abstract: High corrosion resistance of Zn-Al-Mg (ZAM) alloy is widely used in steel wire rope protection. This alloy, however, due to Mg reactivity, easily induced dross formation containing MgZn2 and Mg2Zn11 which reduced the coating integrity. Thus, in this work, Mg is replaced with various wt.% Sb (ZAS) coated on steel surface will via hot-dip process at the eutectic environment. The thickness of the intermetallic layer and coating thickness were observed using an optical microscope and SEM. It was found that 0.3 wt.% Sb improved the corrosion performance 45.5% (0.00267 mmpy) than ZAM coated steel (0.00490 mmpy) under accelerated corrosive medium of 3.5% NaCl.

Abstract: Alloying zinc melt with nickel is used to control the thickness of the zinc coating on steels with different contents of silicon and phosphorus. Nickel is involved in the formation of iron-zinc phases in the coating and inhibits their growth. The use of zinc-nickel master alloys is well studied and has a significant disadvantage - the significant wastage of nickel in the bottom dross. The application of nickel tablets avoids wastage, because it allows us to distribute nickel evenly throughout the bath volume. The aim of this work was to determine the working concentration of nickel introduced into the melt from nickel tablets for a wide range of silicon-containing steels and for a galvanizing time of 2-5 minutes. It was found that the nickel concentration of 0.04% leads to the coating thickness decrease and normalization of the variation in coating thickness on steels with a silicon equivalent SiEV 0.12-0.28% at the galvanizing time of 2-5 minutes, and on high-silicon steel (SiEV 0.75%) at the holding time of 3 minutes. A nickel concentration of 0.03% is effective for SiEV steels 0.12-0.18% with a galvanizing time of 2-3 minutes. "Sandeline Peak" is completely smoothed out with a holding time of 3-5 minutes in the melt with a Ni content of 0.05%. The nickel presence in the zinc melt modifies the ζ-phase structure in the coating, making it more dense and uniform in thickness.

Abstract: Along with high tensile strength, high carbon steel wires must possess sufficient torsional ductility is to avoid longitudinal splitting along the wire axis, known as delamination. Often, wires ductile in the bright (asdrawn) surface condition exhibit delamination failure after undergoing a post-drawing surface treatment such as hot-dip galvanizing. The objectives of this study were to examine the influence of postdrawing heat treatment time and temperature on drawn wire mechanical properties, and to identify possible treatment conditions that suppress delamination. Stelmor cooling or lead patenting prior to drawing were used to develop a pearlitic microstructure. Salt pot heat treatments simulated postdrawing heat treatments; experimental heat treatments were conducted between 325 °C and 475 °C for 20 s or at 450 °C for immersion times between 1 s and 20 s. Tension and torsion tests quantified the changes in mechanical properties due to aging. Lead patented wires experienced greater tensile strength and torsional ductility changes with aging time and temperature when compared to the Stelmor cooled wires. This increased sensitivity was attributed to greater dislocation recovery in the patented wire after drawing.

Abstract: There is a growing demand for Advanced High Strength Steels (AHSS) in the automotive industry owing to their high specific strength and good formability. The mechanical properties satisfy the demands for improved passenger safety and decreased vehicle weight due to thinner cross sections. Hot-dip galvanizing is a common procedure to prevent corrosion of steel, galvanized steel forms the basis for further processing like organic coating. Industrially, the steel strip is annealed at 840 °C in 5 % H₂ in N₂ at a dew point (DP) of -30 °C. These conditions are reducing for Fe, but oxidizing for oxygen-affine alloying elements as Mn, Si and Cr. These ignoble elements form an external, covering oxide layer on the steel surface, which exhibits poor wettability for the Zn(Al, Fe)-bath. The liquid Zn(Al, Fe) has a temperature of 460 °C and contains 0,2 wt% Al to form a Fe₂Al_5-xZn_x-layer to inhibit the growth of Fe-Zn-intermetallics. Along with the increased amount of alloying elements to improve strength and ductility of AHSS the evolving oxide layer after annealing at the steel surface deteriorates hot-dip galvanizing. The question arises what happens to the surface oxides during immersion in the Zn(Fe, Al)-bath. For this purpose annealed as well as annealed and galvanized 0.8Si-AHSS and 1.5Si-AHSS were compared by glow discharge optical emission spectroscopy (GD-OES) depth profiles. Galvanized specimens show fewer oxides at the steel-zinc-interface as annealed specimens. A possible explanation is an aluminothermic reduction of oxides by 0.2 wt% dissolved Al in the Zn(Al, Fe)-bath. Al is thermodynamically more affine to oxygen than Mn and Si and may reduce Mn- and Si-oxides. An alternative theory is the dissolution of Fe in Zn during reactive wetting, as a side effect the oxides are rinsed off too. Additionally, the influence of DP was investigated. According to Wagner’s theory of selective oxidation, a higher amount of oxygen in the annealing atmosphere leads to internal oxidation of the alloying elements. Experiments were carried out with 0.8Si-AHSS and 1.5Si-AHSS by altering the DP during annealing from -30 °C (380 ppm H₂O) to 0 °C (6000 ppm H₂O). Oxidation mode changed from external (DP -30 °C) to internal oxidation along grain boundaries (DP 0 °C), as predicted by Wagner. These oxide-free surface provides good reactivity to enhance reactive wetting with the Zn(Fe, Al)-bath and form a dense Fe₂Al_5-xZn_x-layer.

Abstract: The aim of the research was the indication of the causes of a difference in thickness of the zinc coating on the surface shaped by plasma cutting. The research was focused on fittings for overhead power lines - a double eyes links made of steel S355J2. The prepared materials were cut by plasma. Then, links were subjected to mechanical treatment (shot-blasting) and chemical treatment (pickling, rinsing and fluxing). The hot-dip galvanizing process was performed in industrial conditions by applying the constant temperature equal to 457°C, and a dipping time equal to 150 s. The research was conducted on the link’s flat surface (after rolling) and the side surface (after cutting). The (Zn) - coating morphologies and sub-layer thicknesses were evaluated on the basis of metallographic analysis and corrosion tests (acc. to EN ISO 9227). The correlation between the results of corrosion test and coatings morphology was determined.The observed changes are closely related to the outer layer steel structure (HAZ) which subsequently influences the mechanism and zinc coating growth kinetics

Abstract: The technology of microalloying zinc melt by nickel is widely used to control the thickness of the zinc coating when the machine steels are subject to hot-dip galvanization. However, in some cases inclusions of Ni-Zn-Fe dross are formed on surface of the products, which leads to their deterioration. The aim of this work is to investigate the microstructure, mechanism of formation and elemental composition of this dross. Conditions for the formation of different phases in the coating were analyzed using Ni-Zn-Fe ternary diagram. It was found that Ni-Zn-Fe dross is a ζ-phase containing about 0.5 at. % nickel and isomorphic with FeZn13-phase. The main reasons for the formation of Ni-Zn-Fe dross are Zn-Fe contamination in the melt, the excess nickel concentration (more than 0.06 at.%), and the irregular nickel concentration in the melt. Methods for preventing this type of defects in hot-dip galvanization have been proposed.

Abstract: Hot-dip galvanized fasteners are key connecting components on power transmission towers and structures. In order to improve the installation code of galvanized fasteners, this paper establishes a three-layer (BP) neural network by using the friction coefficients between threads, nut bearing surface friction coefficients and the associated torque coefficients. In addition, the neural network is trained to predict the torque coefficients of fasteners. It can be seen from the research results that the torque coefficients fall within [0.355, 0.709]. Subsequently, the prediction capability of neural network is verified through tests and statistics upon real galvanized fasteners, proving that BP neural network is an effective model.

Abstract: A new type of laminar composite material has been developed by the bonding of ceramic and metal with a special agglutinate metal. A tube can be made of the laminar composite material and this tube can perform as an outer sheath of an immersion heater. Such heaters can be made to lager size and can be heated using a wide range of energy sources including electricity, gas and oil. Moreover this new heater tube is low cost and has a long working life, is convenient to use and requires little maintenance. This technology allows all kinds of zinc kettle to be heated by immersion heaters.

Abstract: This paper compares and discuses coating cracks on the deformed part of galvanizes dual phase steel after standard 0t bend test. And it is further founded that cracks concentrate on areas where the ζ-FeZn₁₃ phase is dense. Further investigation figures out relationships between cracks generation and ζ-FeZn₁₃ phase.

Abstract: Development process of Hot-dip galvanizing technology and characteristics of different production methods were reviewed in this paper. Presently, the UEC method was utilized widely because of its advantages like high output, high quality, energy saving, lower consumption and low products cost. To improved the corrosion resistance of the coating and declining the cost of hot-dip galvanizing, hot-dip galvanizing alloyed coating has been developed. Although the general hot-dip galvanizing has been developed rapidly in China, we should make great efforts to research deeply and improve the hot-dip galvanizing technology, especilly in the areas such as zinc alloy plating and the corresponding hot-dip galvanizing technology.