Hot-dip Coatings Research Articles

Aşınma ve Korozyona Dirençli Çelik Yüzeyler Oluşturmak Için Kullanılan Yüzey İşlemleri Üzerine Bir Derleme

Steel alloys are one of the most used engineering material classes due to their superior properties such as yield and tensile strength, good thermal conductivity, machinability, formability, ductility, magnetic properties, and recyclability. In addition to its advantages, steel suffers from two main factors that limit its use, namely wear and corrosion. Wear and corrosion, separately or in combination, cause a material loss in steel, resulting in increased costs in industrial production. However, with appropriate surface treatments, wear and corrosion of steels can be prevented or kept to a minimum. Corrosion and wear resistances provided by appropriate methods have the potential to reduce costs and also expand the set of suitable materials that designers can choose from. In this study, brief information about steel is given and then preventive applications against wear and corrosion of steel materials are examined. Definitions were made about surface treatments such as hot-dip coatings, electrochemical coatings, electroless coatings, thermochemical surface treatments, sol-gel coatings, chemical vapor deposition (CVD), thermal spray coatings, physical vapor deposition (PVD), and the effects of surface treatments on the wear and corrosion properties of steels were investigated. In addition, the effects of some process parameters of surface treatments and post-treatments such as heat treatment on corrosion and wear behavior are presented.

Galvanic corrosion behavior of hot-dip Al and 55Al–Zn coatings applied to steel bolted joints in atmospheric environments

Atmospheric corrosion is one of the most critical issues in steel structures. To improve the structure's durability and reduce its cost, hot-dip coatings are a significant method for steel protection. The corrosion behavior of Al-based hot-dip coatings has been extensively studied. Galvanic corrosion usually occurs when steel members are coated with different hot-dip coatings and placed in direct contact. In this study, galvanic corrosion of an Al coating in contact with a 55Al–Zn coating in an atmospheric environment was investigated through electrochemical and exposure tests. The galvanic corrosion and its mechanism were studied based on open circuit potential (OCP), galvanic current, and X-ray diffraction (XRD) analyses. This study verified the galvanic corrosion of bolt joints in the actual application by the long-term exposure test. The results suggests that 55Al–Zn coating is a good substitute for Zn coating used for bolted joints in contact with Al-coated steel plate.

Microstructure and Corrosion Behavior of ZnAl12Mg3Si0.3 Double-Batch Hot-Dip Coatings

This article presents the microstructure (SEM) and corrosion behavior of ZnAl12Mg3Si0.3 (ZAMS) coatings obtained by the double hot-dip method on Sebisty steel with increased strength. On the basis of chemical composition studies in micro-areas (EDS) and phase composition studies (XRD), structural components of the coating and corrosion products formed on the coating surface after exposure to the neutral salt spray (NSS) test (EN ISO 9227) were identified. The presence of the Fe(Al,Si,Zn)3 intermetallic phase was found in the Fe-Al intermetallic layer, while in the outer layer, dendrites rich in Al and Zn were identified. In these dendrites, the eutectics of Zn/MgZn2 and precipitates of the MgZn2 phase and Si were located. The NSS test showed better corrosion resistance of ZAMS coatings compared to conventional zinc hot-dip coatings. The increase in corrosion resistance is due to the formation of favorable corrosion products: simonkolleite-Zn5(OH)8Cl2·H2O and hydrozincite-Zn5(OH)6(CO3)2, and the presence of the MgZn2 phase in the coating, which is more anodic than other structural components.

Effect of Hot Dip Plating Process Parameters on Microstructure and Properties of Zinc–10%Aluminum–Mischmetal Alloy Coated for Bridge Cable Steel Wire

In this work, the effect of the hot dip plating process on the microstructure and properties of zinc–10%aluminum–mischmetal (Zn-10Al-MM) alloy coated for bridge cable wire was studied by changing the hot dip plating temperature, time, and cooling mode. An optical microscope was used to observe the microstructure of the coating and steel wire at low power; a GeminiSEM300 field emission scanning electron microscope was used to observe the microstructure of the coating and steel wire at high power. The hot dip planting temperature is 450 °C, the hot dip plating time is 30 s and 45 s, whether water cooling or air cooling, the hot dip coating structure is relatively uniform, and the grain size is small, the hot dip coating thickness is thick. The coating with 450 °C, 45 s, and the water-cooling process has the highest tensile strength. The corrosion resistance of the hot dip coatings under different processes is higher in the salt spray test. Based on the results of the electrochemical test and salt spray test, the best corrosion resistance of the coatings under 450 °C, 45 s, and the water-cooling process is obtained.

Peritectic Structure Evolution and Corrosion Behavior in Hot-dip Zn-Al Alloy Coatings

Peritectic Structure Evolution and Corrosion Behavior in Hot-dip Zn-Al Alloy Coatings

Effect of manganese addition on the appearance, morphology, and corrosion resistance of hot-dip galvanized zinc coating

The study investigates the effect of manganese addition in the hot-dip galvanized zinc coating on steel. The ZnMn hot-dip coatings were prepared under ambient conditions on a steel sheet using a custom-made galvanization simulator. The ZnMn hot-dip coatings were always covered with oxides formed during the withdrawal, giving patchy coloration. A novel approach is demonstrated to prevent patchy coloration due to these oxides and produce alloy coated surfaces with homogeneous coloration. The microstructures of the alloy coated sheets were investigated to identify the effect of the Mn addition. The microstructure changes in the alloy coating due to increasing Mn addition were correlated to the composition, hardness of the individual intermetallic layers, and the basal texture. Compared to the hot-dip Zn coating, Mn addition decreased the corrosion rate (icorr from potentiodynamic polarization test) in the alloy coating by 65%. The Mn addition also controlled the degree of the white rust formation and prolonged the life of the alloy coated steels in accelerated salt spray test (> 300 h of exposure, ASTM B117). The bend test results show that Mn addition does not affect the deformation tolerance of the hot-dip alloy coatings.

The effect of silicon on the structure and properties of hot-dip aluminium-based coatings

The continuous increase in demand for aluminum coatings for the automotive industry is associated with the need to improve their quality in terms of protective and mechanical properties. The aluminum coatings produced hot-dip, on the border with the steel substrate formed intermediate phases FeAl3, and Fe2Al5, which reduce the corrosion resistance and limit the possibility of forming a coated article. The paper determines the effect of the addition of 7% Si to an aluminum coating (690°C/60 s) on the microstructure thickness and type of intermediate phases as well as hardness and surface features. It has been shown that the addition of Si results in a 40 % increase in the hardness of the coating and reduce the surface roughness. In addition, is limited interdiffusion of Al and Fe, as a result of which an intermetallic phase layer is formed, Al7-9Fe2Si enriched phase, 4 times thinner than a coating without the addition of Si, while maintaining the thickness of the outer coating layer.

Perspective on “Atmospheric Corrosion Resistance of Skyward- and Groundward-Exposed Surfaces of Zinc- and 55% Al-Zn Alloy-Coated Steel Sheet,” H.E. Townsend, Corrosion 54, 7 (1998): p. 561-565

Abstract:Twenty-year exposure testing of sheet steel panels with hot-dipped coatings of zinc and 55% Al-Zn alloy at rural, industrial, and marine sites was performed with specimens designed to allo...

High-temperature degradation mechanism of aluminide coatings on titanium alloys under cyclic oxidation at 750°C

ABSTRACTAluminide coatings prepared on Ti-6Al-4V substrate were able to improve oxidation resistance of the alloy under cyclic oxidation at 750°C both in dry and moist air conditions due to aluminide’s ability to form a stable alumina oxide scale. However, degradation of the coating due to spallation, cracking, internal oxidation and formation of voids with increased cyclic oxidation reduced the lifespan of the coating and the underneath substrate. The main cause of coating degradation for hot-dip specimens is cracks that initiated and propagated perpendicular to the surface. For the plasma spray specimens, the cracks are parallel to the surface. Initiation of cracks in hot-dip coatings are more accredited to residual stresses due to cooling and presence of brittle intermetallic phases TiAl2 and TiAl. For plasma spray coatings, initiation and propagation of cracks are attributed to presence of entrapped oxides, pores and grain boundaries of the deposited splats whose flattened edges are parallel to the surface of the coating. Presence of water vapor, too, acts as an oxygen carrier and thus promotes oxidation internally, inhibits growth of continuous protective alumina oxide scales and weakens the scale/alloy interfacial toughness. Water vapor therefore accelerates degradation by increasing spallation and cracking rate of the coating.

Influence of Hydrogen Sulfide on the Corrosion-Electrochemical Properties of 20 Steel with Coatings Based on Zinc and Aluminum

We study the corrosion of a hot-dip zinc coating and arc-sprayed aluminum and zinc coatings in chloride- acetate solutions and model seawater saturated with hydrogen sulfide. It is shown that, in chloride–acetate solutions, hydrogen sulfide promotes an increase in the corrosion rate of 20 steel by more than an order of magnitude. For the hot-dip zinc coatings, hydrogen sulfide does not change the corrosion rate, whereas for the arc-sprayed coatings, it decreases the corrosion rate by a factor of ∼ 5. The saturation of model seawater with hydrogen sulfide decreases the corrosion rate of 20 steel by a factor of ∼ 7 and the corrosion rate of the hot-dip zinc coating by a factor of ∼ 1.4 but does not affect the corrosion rate of the arc-sprayed coating. The insoluble corrosion product of zinc, namely, its sulfide, does not passivate these coatings. Hydrogen sulfide leads to an insignificant increase in the corrosion rate of the arc-sprayed aluminum coating both in a chloride–acetate solution and in model seawater. Its values are 3–7 times lower than for 20 steel, which indicates the possibility of application of the coatings based on aluminum for the corrosion protection of steels in hydrogen-sulfide-containing media.

AlSi ALLOYS FOR MAGNETRON DEPOSITION OF THE COATINGS ON CAR EXHAUST MUFFERS – FORECAST OF TECHNOLOGICAL WEAR

In the production of car exhaust system parts, for protection against corrosion and high-temperature oxidation, alumina and AlSi alloy hot-dip coatings are currently especially effective. The authors of this study are conducting investigations into the application of AlSi alloys made by the traditional casting technology to the fabrication of AlSi PVD coatings by the magnetron sputtering method. For the purposes of the present study, three discs of AlSi alloys were subjected to magnetron sputtering. The assessment of the wear of the discs was made by microscopic observations, by mapping the geometric features and roughness of the disc surface with a profilometer, and by making the statistical analysis of the results by the bootstrap method. A similar degree of wear of discs made of all the examined alloys, expressed as the depth of losses, was shown. It was also fund that the surface of discs of alloys with a higher silicon content was characterized by a lower roughness compared to the AlSi7 alloys. The wear rate of discs in the PVD process was estimated at approx. 150 m/h.

Laser resurfacing of Al–Zn–Mg–Si coatings

The feasibility of refinement of Al–Zn–Mg–Si hot dip coatings by diode laser resurfacing has been demonstrated. The microstructure of the laser resurfaced coatings was characterised mainly by transmission electron microscopy and also by scanning electron microscopy. The variance of heat input results in different cooling rates and varying degrees of refinement; that is, the higher the power density, the lower the cooling rate and the larger the secondary dendrite arm spacing of α-Al dendrites. In addition, the inherent variation of chemical composition in coatings also affects the microstructure as well as phase distribution. This laser resurfacing technique has not only reduced the secondary dendrite arm spacing/α-Al dendrites but also changed the solidification path and produce different phases and microstructure in the interdendritic areas.

THE ABRASION OF AL-SI COATINGS WITH DIFFERENT SILICON CRYSTAL MORPHOLOGY, APPLIED IN AUTOMOTIVE SILENCERS

This paper compares the abrasibility of aluminium-silicon coatings with silicon crystals of various forms. The tests were performed on Al-Si coatings with the chemical comp67890-osition corresponding to that of hypoeutectic and peritectic silumins (6-10wt% Si), manufactured by hot-dipping on type X2CrTi12 steel and by cold cladding with 60% cold reduction on AlMn1Cu alloy. The hot-dip coatings deposited on X2CrTi12 steel were investigated as made and after a two-stage heat treatment: 420oC/2h/water and 120oC/2h/air. The morphology, shape, and size of silicon crystals in the coatings were studied under a microscope and with the image analysis technique (determining the shape factor among other parameters). Image analysis was also applied to the evaluation of abrasive wear resistance of the coatings using a ball wear test. Their adhesion strength was tested with the scratch test method. The test results indicated that the change in Al-Si coating silicon crystal morphology (from large sharp edged and needle-like to smaller rounded particles) was heat induced, which, compared to the pre-treatment condition, lowered abrasion resistance values and produced a more uniform abrasion loss. This condition was regarded as more desirable in terms of maintaining the coating continuity during drawing, with no risk of spalling. It was also demonstrated that clad Al-Si coatings could provide an alternative solution for the widely used hot dip coatings on steel sheet.

Resistance of different Zn coatings at elevated temperature air environments

In this work, the structure and oxidation behaviour of three different zinc coatings were examined. The coatings were formed with hot dip galvanizing, pack cementation and thermal spray methods. Three different oxidation conditions were selected for the tests, which correspond to low, medium and intensive oxidation conditions. The oxidized samples were examined by scanning electron microscopy and X-ray diffraction. Results showed that the thermal spray coatings are far more susceptible than the others and suffer from extreme oxidation because of the porous net existing in the coating, which provides diffusion paths to oxygen. Hot dip and pack coatings were proved more resistant under the same exposure conditions, mainly due to the presence of different Fe–Zn phases in their structure and their morphological homogeneity.

Furnace Roll Failure Analysis on Hot-Dip Coating Line Spurs New Design and Welding Process

Abstract A new design and welding process may extend the life of furnace rolls in hot-dip coating lines, which often fail in less than one year. This article is a case study of analysis of a failed furnace roll that led to a proposed improved design to extend component life.

Electrochemical Corrosion Behavior of AISI 409L Stainless Steel Aluminized by Hot-Dip Coating Method in Automotive Exhaust Gas Solution

Electrochemical Corrosion Behavior of AISI 409L Stainless Steel Aluminized by Hot-Dip Coating Method in Automotive Exhaust Gas Solution

Study of the Temperature Effect on the Structure and Thickness of Hot-Dip Zinc Coatings on Fixing Products

Hot-dip galvanizing of steels is usually performed by immersing the metal in a bath with molten zinc in the temperature range from 450 to 460 °C. In some cases it is necessary to obtain a minimal coating thickness. For example, high-strength bolts and other fixing products require a minimal thickness of the coating because a too thick zinc coating requires additional work on re-threading, which leads to spalling of coatings, a loss of corrosion resistance and, consequently, failure of the entire product. The main aim of this work was to study the influence of elevated temperatures of hot-dip galvanizing on the thickness and microstructure of zinc coatings on bolts and nut preform. The microstructure and elemental composition of the coating were studied by scanning electron microscopy and energy dispersion X-ray microanalysis. It was found that the coating thickness obtained in the range between 475 and 535°C decreases with temperature and reaches a minimum at 535°C. The structure of the coating after high-temperature hot-dip galvanizing was fundamentally different from the structure of the coating made at standard temperatures 450-460°C. This coating formed at 535°C was dense, homogeneous, non-porous and composed of a mixture of the δ and ζ-phases without distinct phase boundaries. That’s why it was recommended to maintain the bath temperature in the range between 533°C and 537°C. It allows us to obtain a hot-dip galvanized coating of a minimal thickness and a good quality on fixing products.

Structural Properties of Zinc and ZnMgAl Coatings on Steel Sheets

In the paper mutual comparison of zinc coatings enriched with small additions of Mg and Al (up to 1 wt.% Mg and 1 wt.% Al) and traditional zinc coatings produced by hot dip galvanizing, concerning some important properties of coatings like coating structure, cracks formation after deformation and corrosion resistance of deformed samples was studied. It was shown, that while traditional hot-dip zinc coatings are formed by homogenous zinc layer, exhibiting only low amount of soluble aluminium, coatings enriched by small amounts of Mg and Al, namely 0.6% Mg and 0.8% Al are formed by dendritic zinc matrix and interdendritic phase containing Zn-Mg-Al eutectics. Development of cracks was investigated in the area of maximal deformation of the samples subjected to stretching. It was found, that while traditional zinc coatings showed sporadic long fine cracks, zinc coatings enriched with Mg and Al exhibited aggregation of short thick cracks in the deformed area. Samples of both materials after stretching were also exposed in neutral salt spray atmosphere in corrosion chamber. It can be concluded, that material with coatings enriched with Mg and Al showed better results in corrosion tests contrary to the presence of massive cracks in the coating. This significantly increased corrosion resistance is possible due to excellent adhesion of zinc coatings, containing Mg and Al on drawing steels.

Adhesion of Zinc Hot-dip Coatings

The work is focused on verification of quality adhesion of zinc coating. It describes elements which affect quality and adhesive solidity within the coating. For assessment itself it will be neccessary to get know the basic elements which can affect adhesion of hot-dip coating which will be essential for choosing suitable samples for verification itself. These elements characterise acoustic responses during delamination coating. They affect elements influencing progress of signal. In research there is also a summary of existing methods for testing adhesion of coatings. As a result a new proposal of a new method comes out for purpose of quality testing of adhesion zinc hot-dip coating. The results of verification of this method are put to scientific analysis and findings lead to assessment of proposed method and its application in technical practise.The goal of this contribution is also include to proposed methodology testing adhesion zinc coating by nondestructive diagnostic method of acoustic emission (AE), which would monitor characterise progress of coating delamination of hot-dip zinc from basic material in way to adhesion tests would be practicable in situ. It can be enabled by analysis and assessment of results acquired by method AE and its application within verification of new method of adhesion anti-corrosive zinc coating.

Kinetics of Growth and Structure of Coatings Obtained on Sandelin Steels in the High-Temperature Galvanizing Process

In the paper the author presents the results of tests defining the characteristics of behaviour of Sandelin steel in the high-temperature galvanizing process. The growth kinetics of hot-dip zinc coatings on the substrate of 0.05% Si steel in the temperature range of 540-580°C has been established. The structure of the coatings and their phase composition have been developed and the chemical composition of structural components of the coating has be defined. It has been determined that the coating is composed of a compact layer δ1 and an area of a two-phase mixture of δ1 and Zn. The conducted tests confirmed the presence of phase Γ1 , which does not form a continuous layer but it forms individual precipitates which are irregular in shape. The growth kinetics of the coating indicates that an increase in temperature causes a decrease in the coating thickness, which might prove that dissolving processes prevailed over the processes of diffuse coating growth.