Hot-dip Aluminizing Research Articles

Preliminary study of HDA coating on CLAM steel followed by high temperature oxidation

A hot-dip aluminizing process is expected to produce aluminide coatings on structural materials to resist tritium permeation, corrosion, and magnetohydrodynamic (MHD) effects in the fusion reactor blanket. China Low Activation Martensitic (CLAM) steel, which is the candidate structural material for the LiPb blanket system in China, was coated with pure aluminum and with an Al–Si alloy. Factors affecting the thickness and morphology of the aluminide coatings were studied. After the hot-dipping treatment, FeAl3 and Fe2Al5 were observed at the Al/steel interface. The existence of silicon in the molten aluminum suppressed the growth of Fe2Al5, built up the thickness of FeAl3 slightly, and contributed to reducing the thickness of the intermetallic layer. The brittle phase of Fe2Al5 had completely transformed to ductile phases of FeAl2, FeAl and α-Fe(Al) after high temperature heat-treatment in air. Kirkendall voids were found in the diffusion layer, due to the rapid interdiffusion of iron and aluminum during oxidation. Cracks and pores were observed on the coating surface and at the interlayer. Grazing incidence X-ray diffraction indicates the presence of α-Al2O3 in the oxide layer.

Aluminising of Mild Steel Plates

Hot dip aluminising of low carbon steel was done at temperatures 690°C and 750°C for dipping time ranging from 300 to 2400 seconds. During aluminising a mixture of ZnCl2 and NH4Cl was used as flux. During aluminising components of the flux decomposed and zinc formed interacted with the Fe and Al. The aluminised samples were characterised for iron-aluminium intermetallic layer formation, morphology, and local composition. It was observed that intermetallic layer was predominantly Fe2Al5 and FeAl3 at 690°C and at 750°C coating consisted of FeAl3 layer and a layer with Al/Fe ratio greater than 3.26. For both temperatures, coating thickness increased with increase in time. For a given dipping time, deposition was less at higher temperature and this is attributed to changes in the kinetics of growth of individual layers due to dissolved zinc in the aluminium, at 750°C. Also, spalling of intermetallic layers was observed at elevated temperatures and longer dipping times.

The Influence of Temperature on the Oxide Layer Formation of Aluminized Carbon Steel

The growth of thin oxide layer due to the variation in temperature on the surface of aluminized carbon steel was investigated. Hot dip aluminizing of low carbon steel was carried out at 750 °C in a molten pure aluminum for 5 minutes. Aluminized samples were heat treated at 600 °C, 700 °C, 800 °C, and 900 °C for 1 hour. The formation of aluminum oxide layer was investigated in this study. Optical microscopy, Atomic Force Microscopy (AFM), SEM and EDAX were used in investigation. From the observation, the appearance of aluminum oxide layer increased with the increase in temperature. The result of EDAX analysis revealed the existence alumina phase. Surface roughness measurement showed increment with the increase in oxidation heat treatment temperature.

A Study of Double-Coating of Hot-Dip Aluminizing

Double-coating of hot-dip aluminizing is a process of protecting steel from being oxidized. The process is featured that the component is firstly hot-dip galvanized and finally hot-dipped with aluminum. The comparison of interface morphology was conducted for single hot-dip aluminizing and double-coating of hot-dip aluminizing on Q235 steel sheets. The metallographies of the cross-sections were observed and analyzed with SEM, XRD and EDS, respectively for the specimens prepared by the two processes. The experimental results indicate that there is no Zn-Fe alloy layer formed in the double-coating, and both single and double coating have similar phase compositions. However, the interface between the alloy layer and the steel matrix is smoother for the double-coating than that for single-coating.

Improving Corrosion Resistance of the Hot-Dip Aluminum Coating on 22MnB5 Steel Surface

Keywords: Hot-Dip Aluminum; Corrosion resistance; Fe-Al Intermetallic alloys Abstract. The hot-dipping Al coating was developed on 22MnB5 steel surface. Effects of corrosion resistance with different dipping time coatings were investigated in this paper. It is describes an approach to improve the corrosion resistance of 22MnB5 steel. The results of the polarization curves show that the dipping 2min coatings have the highest corrosion potential (Ecorr) and the lowest corrosion current (icorr), indicating that this coating is a best corrosion inhibitor. It is similar results with EIS for corrosion resistance, respectively. The proper thickness (~20µm) of Fe-Al compounds between Fe substrate and Al coatings must be selected (750°C, hot-dipping 2min) in order to improve corrosion resistance for 22MnB5 steel.

High-temperature oxidation of hot-dip aluminizing coatings on a Ti3Al–Nb alloy and the effects of element additions

Hot-dip aluminizing and interdiffusion treatment were used to develop TiAl3-rich coatings on a Ti3Al–Nb alloy. The addition of Si, Mn, or Ag to the coatings improves the thickness uniformity and reduces the formation of the through-thickness transverse cracks. The element additions promote the formation of dense and continuous Al2O3-rich scales during the high-temperature oxidation. A layered structure of Al2O3/TiAl3/(TiAl3+TiAl2)/TiAl/Ti-depleted alloy/alloy from the outside to the inside forms after oxidation at 900°C without changing the main body of the Si- or Mn-modified coating, and the Ag-modified coating develops a layered structure of Al2O3/TiAl3/(TiAl3+TiAl2)/(TiAl2+TiAl3)/TiAl/alloy.

Study on the Factors Influencing Plating Coat Thickness in Ultrasonic-Aided Hot-Dip Aluminizing Facing Remanufacturing

An aluminum layer can be gotten on the worn-out work piece surface through ultrasonic-aided hot-dip and converted into alumina layer having wear-resistance performance though micro arc oxidation which can realize remanufacturing. The key technology of hot-dip aluminizing phase in above remanufacturing process is controlling the plating coat thickness. The influences of withdrawing speed, hot-dip temperature and hot-dip time on the plating coat thickness are analyzed in this paper.

TEM Analysis and Corrosion Resistance of the Ceramic Coatings on Q235 Steel Prepared by Hybrid Method of Hot-Dipping Aluminum and Plasma Electrolytic Oxidation

The hybrid method of plasma electrolytic oxidation (PEO) and hot-dipping aluminum (HDA) was employed to deposit composite ceramic coatings on the surface of Q235 steel. The cross-section microstructure and surface morphology of the treated specimens were investigated with scanning electron microscopy (SEM). Especially, the composition of the composite coatings was investigated with transmission electron microscopy (TEM). The corrosion resistance was analyzed by immersing and corrosion polarizing experiments. The results indicate that metallurgical bonding can be observed between the ceramic coatings and the steel substrate. There are many micro-pores which act as discharge channels in the PEO coatings. The phase composition of the ceramic coatings is mainly composed of amorphous phase and crystal Al2O3 oxides. The crystal Al2O3 phase includes κ- Al2O3, θ- Al2O3 and β- Al2O3.The corrosion resistance of the PEO samples is much better than that of the HDA samples whether immersed in the NaCl solution or in the sea water.

Formation Behavior of an Intermetallic Compound Layer during the Hot Dip Aluminizing of Cast Iron

Formation Behavior of an Intermetallic Compound Layer during the Hot Dip Aluminizing of Cast Iron

Effect of hot-dip aluminizing on the oxidation resistance of Ti–6Al–4V alloy at high temperatures

Hot-dip aluminizing and interdiffusion treatment were used to develop a TiAl3-rich coating on Ti–6Al–4V alloy. Interrupted oxidation at temperatures from 600 to 900°C and isothermal oxidation at 700 and 800°C of the coating were conducted. The coating markedly decreases the oxidation rate in comparison with the alloy at temperatures below 800°C during the interrupted oxidation. The oxidation kinetics follows parabolic relations at 700 and 800°C during the isothermal oxidation. A layered structure of Al2O3/TiAl3/TiAl2/TiAl/alloy from the outside to the inside forms after oxidation at 700°C without changing the main body of the coating.

TEM analysis and wear resistance of the ceramic coatings on Q235 steel prepared by hybrid method of hot-dipping aluminum and plasma electrolytic oxidation

The hybrid method of PEO and hot-dipping aluminum (HDA) was employed to deposit composite ceramic coatings on the surface of Q235 steel. The composition of the composite coatings was investigated with X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The cross-section microstructure and micro-hardness of the treated specimens were investigated and analyzed with scanning electron microscopy (SEM) and microscopic hardness meter (MHM), respectively. The wear resistance of the ceramic coatings was investigated by a self-made rubbing wear testing machine. The results indicate that metallurgical bonding can be observed between the ceramic coatings and the steel substrate. There are many micro-pores and micro-cracks, which act as the discharge channels and result of quick and non-uniform cooling of melted sections in the plasma electrolytic oxidation ceramic coatings. The phase composition of the ceramic coatings is mainly composed of amorphous phase and crystal Al2O3 oxides. The crystal Al2O3 phase includes κ-Al2O3, θ-Al2O3 and β-Al2O3. The grain size of the κ-Al2O3 crystal is quite non-uniform. The hardness of the ceramic coatings is about HV1300 and 10 times higher than that of the Q235 substrate, which was favorable to the better wear resistance of the ceramic coatings.

주철 - 알루미늄 합금의 Hot Dip Aluminizing시 흑연 및 금속간화합물 층의 형성 거동

Hot dip aluminizing (HDA) is widely used in industry for improving corrosion resistance of material. The formation of intermetallic compound layers during the contact between dissimilar materials at high temperature is common phenomenon. Generally, intermetallic compound layers of and are formed at the Al alloy and Fe substrate interface. In case of cast iron, high contact angle of graphite existed in the matrix inhibits the formation of intermetallic compound layer, which carry with it the disadvantage of a reduced reaction area and mechanical properties. In present work, the process for the removal of graphite existed on the surface of specimen has been investigated. And also HDA was proceeded at for 3 minutes in aluminum alloy melt. The efficiency of graphite removal was increased with the reduction of particle size in sanding process. Graphite appears to be present both in the region of melting followed by re-solidification and in the intermetallic compound layer, which could be attributed to the fact that the surface of cast iron is melted down by the formation of low melting point phase with the diffusion of Al and Si to the cast iron. Intermetallic compound layer consisted of and , the layer formed at cast iron side contained lower amount of Si.

Interfacial reaction of intermetallic compounds of ultrasonic-assisted brazed joints between dissimilar alloys of Ti [sbnd]6Al [sbnd]4V and Al [sbnd]4Cu [sbnd]1Mg

Ultrasonic-assisted brazing of Al 4Cu 1Mg and Ti 6Al 4V using Zn-based filler metal (without and with Si) has been investigated. Before brazing, the Ti 6Al 4V samples were pre-treated by hot-dip aluminizing and ultrasonic dipping in a molten filler metal bath in order to control the formation of intermetallic compounds between the Ti 6Al 4V samples and the filler metal. The results show that the TiAl 3 phase was formed in the interface between the Ti 6Al 4V substrate and the aluminized coating. For the Zn-based filler metal without Si, the Ti 6Al 4V interfacial area of the brazed joint did not change under the effect of the ultrasonic wave, and only consisted of the TiAl 3 phase. For the Zn-based filler metal with Si, the TiAl 3 phase disappeared and a Ti 7Al 5Si 12 phase was formed at the interfacial area of the brazed joints under the effect of the ultrasonic wave. Due to the TiAl 3 phase completely changing to a Ti 7Al 5Si 12 phase, the morphology of the intermetallic compounds changed from a block-like shape into a lamellar-like structure. The highest shear strength of 138 MPa was obtained from the brazed joint free of the block-like TiAl 3 phase.

Tribological investigation on friction and wear behaviour of coatings for hot sheet metal forming

Abstract Since hot sheet metal forming has become a key technology to produce high strength steel parts for modern automotive construction, detailed knowledge of tribological behaviour of coated steel blanks at elevated temperatures is necessary. Therefore, hot dip aluminium–silicium and electro-plated zinc alloy coatings for hot forming applications have been evaluated according to their friction and wear behaviour. The coefficient of friction was revealed in hot strip drawing experiments. Moreover, mass loss of the workpiece has been measured to characterize the amount of wear. According to the different constitution of the Al–Si coating in comparison to the electro-plated Zn–Ni after heat treatment, the zinc alloy coating showed higher mass loss but lower coefficient of friction. Additionally, wear characteristics have been evaluated in hot forming tests. Herein, parts formed of Al–Si coated blanks showed as well a lower mass loss but more aggressive wear behaviour by means of adhesive wear to the die, resulting in metallic build-up onto the die radius. In contrast, the workpiece related mass loss was higher for Zn–Ni but considerable metallic build-up layers onto the die did not occur. This may be advantageous in production lines hence maintenance and reconditioning frequency of the forming tools could be reduced.

Influence of Temperature and Oxygen Pressure on the Oxidation Process for Preparing Tritium Permeation Barrier

In ITER D-T fuel will be used for fusion plasma. Therefore a material capable of acting as a tritium permeation barrier on stainless steel is required. It is well known that thin alumina layer can reduce the tritium permeation rate by several orders of magnitude. A technology is introduced here to form a ductile Fe/Al layer on the steel with an alumina over-layer, which consists of two main steps, hot-dip aluminizing (HDA) and subsequent oxidation process. According to the experiments that have been done, Fe-Al intermetallic layer and outer aluminum coat were formed after the HDA process. In this report, we have studied the influence of temperature and oxygen pressure on the formation of ductile phases and alumina over-layer in the oxidation treatment. At the temperature of 900°C, the brittle Fe-Al intermetallic layer and aluminum coat transformed into ductile phase (FeAl and α-Fe(Al)) and a γ-Al2O3 over-layer was formed under the oxygen pressure about 5Pa. It was found that the low pressure of environment suppressed the formation of pores or cracks as well.

Heat Transfer during the Solidification of Hot Dip Aluminizing Coating

Hot dip aluminizing is one of the most effective methods of surface protection for steels and is gradually gaining popularity.Although the pulling speed is one of the most important parameters to control the coating thickness of aluminizing products,however,there are few publications on the mathematical modeling of pulling speed during the hot dip process.In order to describe the correlation among the pulling speed,coating thickness and solidification time,the principle of mass and heat transfer during the aluminizing process is investigated in this paper.The mathematical models are based on Navier-Stokes equation and heat transfer analysis.Experiments using the self-designed equipment are carried out to validate the mathematical models.Specifically,aluminum melt is purified at 730 ℃.The Cook-Norteman method is used for the pretreatment of Q235 steel plates.The temperature of hot dip aluminizing is set to 690 ℃ and thedipping time is set to 3 min.A direct current motor with stepless speed variation is used to adjust the pulling speed.The temperature change of the coating is recorded by an infrared thermometer,and the coating thickness is measured by using image analysis.The validate experiment results indicate that the coating thickness is proportional to the square root of pulling speed for the Q235 steel plate,and that there is a linear relationship between coating thickness and solidification time when the pulling speed is lower than 0.11 m/s.The prediction of the proposed model fits well with the experimental observations of the coating thickness.

Evolution of micro-arc oxidation behaviors of the hot-dipping aluminum coatings on Q235 steel substrate

Micro-arc oxidation (MAO) is not applicable to prepare ceramic coatings on the surface of steel directly. In this work, hybrid method of MAO and hot-dipping aluminum (HDA) were employed to fabricate composite ceramic coatings on the surface of Q235 steel. The evolution of MAO coatings, such as growth rate, thickness of the total coatings, ingrown and outgrown coatings, cross section and surface morphologies and phase composition of the ceramic coatings were studied. The results indicate that both the current density and the processing time can affect the total thickness, the growth rate and the ratio of ingrown and outgrown thickness of the ceramic coatings. The total thickness, outgrown thickness and growth rate have maximum values with the processing time prolonged. The time when the maximum value appears decreases and the ingrown dominant turns to outgrown dominant little by little with the current density increasing. The composite coatings obtained by this hybrid method consists of three layers from inside to outside, i.e. Fe–Al alloy layer next to the substrate, aluminum layer between the Fe–Al layer and the ceramic coatings which is as the top exterior layer. Metallurgical bonding was observed between every of the two layers. There are many micro-pores and micro-cracks, which act as discharge channels and result of quick and non-uniform cooling of melted sections in the MAO coatings. The phase composition of the ceramic coatings is mainly composed of amorphous phase and crystal Al2O3 oxides. The crystal Al2O3 phase includes κ-Al2O3, θ-Al2O3 and β-Al2O3. Compared with the others, the β-Al2O3 content is the least. The MAO process can be divided into three periods, namely the common anodic oxidation stage, the stable MAO stage and the ceramic coatings destroyed stage. The exterior loose part of the ceramic coatings was destroyed badly in the last period which should be avoided during the MAO process.

Study on the Green Remanufacturing of Ultrasonic Vibration Aided Hot-Dip Aluminizing and Micro Arc Oxidation

In this paper alumina ceramic layer on worn stainless steel work piece was gotten using ultrasonic vibration aided hot-dip aluminizing and micro arc oxidation to realize green remanufacturing. Aluminum layer was gotten on the surface of stainless steel work piece using ultrasonic vibration aided hot-dip aluminizing method. The action mechanism of the hot-dip aluminizing process and the influence of ultrasonic vibration to hot-dip aluminizing process were studied and the best process parameters were achieved. Alumina ceramic layer of high hardness and wear resistance was achieved using micro arc oxidation method. The influence of current density to the characteristic of ceramic layer was investigated. The technology described in this paper can be used for the remanufacturing of worn stainless steel work piece.

Effect of Water Rinsing Temperature for Steel Substrate on Corrosion Behavior of Hot-Dip Aluminizing Coatings

The relationship between the morphology and protective action of hot-dip aluminizing coatings on Q235 steel have been investigated by SEM, EDS and EIS in 3.5 wt% NaCl aqueous solution. The results indicated that the anti-corrosion performance of the hot-dip aluminizing coatings using steel substrate rinsed by the distilled water at 25 oC was higher than that at 80 oC. The evolution of localized corrosion from pitting to exfoliation corrosion has been found on the aluminum coating surface during immersion, and corresponding equivalent circuit models were proposed to fit the EIS data in the initiation and propagation stages of corrosion process.

The Investigation of Hot-Dip Aluminum and Micro-Arc Oxidation Multilayer Coating on 080A15 Steel

By the combined process of hot-dip aluminum and micro-arc oxidation, multilayer ceramic coatings were obtained on the surface of commercial 080A15 steel plates. The microstructures and chemical elements of the coatings were investigated by means of scanning electron microscopy (SEM) and energy-dispersive spectrometry (EDS), respectively. The results show that the conversion coating on the surface of 080A15 steel plate is mainly composed of three layers, they are the outer layer of alumina ceramic coating, the middle layer of pure aluminum, and the inner layer of FeAl intermetallic compound. The FeAl intermetallic compound layer appears as branch-like to grow into the steel substrate. The alumina ceramic layer is a porous structure attached on the pure aluminum layer. The distribution of composition elements on the interface between the each layer is gradient transition, which is one of metallurgical adhesive characteristics.