Fe-Al Alloy Layer Research Articles

Study of Hot-Dip Aluminium Plating Based on Micro-Morphology and Coating Bond Strength

Hydrogen barrier coatings with Al2O3 as the main component are a good choice for solving the hydrogen embrittlement problem during hydrogen transportation in long-distance pipelines. However, the difference in the coefficients of thermal expansion between the substrate and the Al2O3 coating limits its further utilisation and development. In this study, rare earth oxides were added to the molten aluminium solution, and a Fe-Al transition layer was introduced on the surface of X80 steel by hot-dip plating to solve the thermal mismatch. Here, the microstructure and bonding strength of the hot-dip aluminium layer were investigated. It is found that the hot-dip aluminium coating consists of the outermost aluminium-rich layer and the inner Fe-Al alloy layer, and the microstructure of the two will change with the change in dip plating parameters. The best overall performance of the hot-dip aluminium layer was obtained from X80 steel substrate at a dip plating temperature of 700 °C and a dip plating time of 5 min. This coating has a good interface, moderate thickness, and a bond strength of 49 N. This study provides a reference value for solving the thermal mismatch between the steel substrate and the Al2O3 hydrogen barrier coating generated by subsequent anodising.

Experimental Measurements and Kinetic Investigation of Fe-Al Alloy Layer During the Galvanizing Process

Experimental Measurements and Kinetic Investigation of Fe-Al Alloy Layer During the Galvanizing Process

Defect Formation in Aluminum-coated Steel by Heat Treatment

A carbon tool steel plate was coated with an aluminum foil with a thickness of 100 μm by explosive welding. This aluminum-coated steel was heat-treated in the temperature range of 973−1273 K for up to 3.6 ks in the atmosphere to form a Fe-Al alloy layer on the steel surface. The alloy layer was basically composed of Fe2Al5, two kinds of FeAl (Al-rich FeAl and Fe-rich FeAl), Fe3Al containing carbon (Fe3Al(C)) and ferrite stabilized by aluminum diffusion (α-Fe(Al)). FeAl2 was also detected together with Fe2Al5 at more than 1223 K. At 1273 K, island-shaped Fe3Al(C) was produced in α-Fe(Al), and the Fe-rich FeAl/α-Fe(Al) interface became indistinct. In addition, defects like a crack and a void were observed in the vicinity of Fe-rich FeAl. The purpose of the present study is to investigate the reason for the defect formation. Various heat treatments were conducted for the aluminum-coated steel, and it was found that a temperature-rising step was responsible for the defect formation. This consideration got support from the results of two-step heat treatment, which was a heating process at 1273 K immediately after holding for 600 s near the eutectoid temperature in the Fe-C binary system.

Preparation of Fe-Al alloy layer on CLAM steel

Reduced activation ferritic/martensitic steel is one of the candidate materials for tritium breeding module in the fusion reactor. In order to control the permeability of tritium in an acceptable range, coating with low hydrogen isotope permeability, known as tritium permeation barrier, is usually prepared on the surface of such structural materials. The FeAl/Al<sub>2</sub>O<sub>3</sub> is the first choice of tritium permeation barrier for many countries, because of its fine performance of high permeation reduction factor, corrosion resistance and high-temperature resistance. The surface morphology and microstructure of Fe-Al infiltrated layer have important influence on the quality of Al<sub>2</sub>O<sub>3</sub> coating. In this study, Al coating on the surface of CLAM steel is prepared by electroplating of aluminum from AlCl<sub>3</sub>-EMIC. Then the Fe-Al infiltrated layer is obtained by diffusion between Al and substrate by annealing. The effects of annealing time and temperature on the microstructure of Fe-Al infiltrated layer are studied by X-ray diffraction, scanning electron microscope and energy dispersive spectrometer. The results show that 20-μm-thick aluminum coating is obtained on the CLAM steel surface by electroplating. The Al coating is uniform and compact, and the size of its surface columnar grain decreases with electroplating current density increasing. Annealing results show that neither hole nor gap is observed between the Fe-Al infiltrated layer and the substrate. In addition, the infiltrated layer is found to be tightly bound to the substrate with a thickness ranging from 7 μm to 45 μm, depending on the annealing parameters. At the initial stage of annealing, Cr enriched Fe-Al alloy is formed evidently. However, such a Cr enrichment disappears at higher annealing temperature or longer annealing time due to diffusion. The surface of infiltrated layer changes from aluminum-rich phase to aluminum-poor phase, and its thickness increases with annealing time or temperature rising. The temperature dependence of the growth rate of Fe-Al infiltrated layer can be described by Arrhenius equation. At this time, the Arrhenius activation energy of aluminization on CLAM steel is calculated to be 78.48 kJ/mol. At 640 ℃ and 760 ℃, the growth of Fe-Al infiltrated layer is controlled by the grain boundary as well as the volume diffusion. When the reasonable thickness and microstructure of Fe-Al alloy layer are used and annealing time or temperature keeps as low as possible, the optimal annealing temperature and time are 700 ℃/10 h, respectively.

EFFECT OF Mg AND TEMPERATURE ON Fe–Al ALLOY LAYER IN Fe/(Zn–6%Al–x%Mg) SOLID–LIQUID DIFFUSION COUPLES

Fe/(Zn–6%Al–[Formula: see text]%Mg) solid–liquid diffusion couples were kept at various temperatures for different periods of time to investigate the formation and growth of the Fe–Al alloy layer. Scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD) were used to study the constituents and morphology of the Fe–Al alloy layer. It was found that the Fe2Al5Znxphase layer forms close to the iron sheet and the FeAl3Znxphase layer forms near the side of the melted Zn–6%Al–3%Mg in diffusion couples. When the Fe/(Zn–6%Al–3%Mg) diffusion couple is kept at 510[Formula: see text]C for more than 15[Formula: see text]min, a continuous Fe–Al alloy layer is formed on the interface of the diffusion couple. Among all Fe/(Zn–6%Al–[Formula: see text]%Mg) solid–liquid diffusion couples, the Fe–Al alloy layer on the interface of the Fe/(Zn–6% Al–3% Mg) diffusion couple is the thinnest. The Fe–Al alloy layer forms only when the diffusion temperature is above 475[Formula: see text]. These results show that the Fe–Al alloy layer in Fe/(Zn–6%Al–[Formula: see text]%Mg) solid–liquid diffusion couples is composed of Fe2Al5Znxand FeAl3Znxphase layers. Increasing the diffusing temperature and time period would promote the formation and growth of the Fe–Al alloy layer. When the Mg content in the Fe/(Zn–6%Al–[Formula: see text]%Mg) diffusion couples is 3%, the growth of the Fe–Al alloy layer is inhibited. These results may explain why there is no obvious Fe–Al alloy layer formed on the interface of steel with a Zn–6%Al–3%Mg coating.

Microstructural Evolution of 11Al-3Mg-Zn Ternary Alloy-Coated Steels During Austenitization Heat Treatment

This study details the microstructural evolution of a commercial hot-dip 11Al-3Mg-Zn-coated steel during austenitization. After 5 minutes of austenitization at 1173 K (900 °C), the ternary alloy coating transformed to consist of a nearly pure Zn as the major layer, a Fe-Al alloy layer at the interface, and a thin oxide overlay. The Fe-Al alloy layer effectively acted as the inhibition layer to prevent Fe from diffusing and reacting with Zn, which in turn retained the molten Zn layer and the integrity of the surface oxide layer. Moreover, the potential difference between the 11Al-3Mg-Zn coating and the steel substrate remained similar after austenitization, signifying the resulting coating kept its sacrificial protection capability.

High temperature corrosion of hot-dip aluminized steel in Ar/1%SO2 gas

Carbon steels were hot-dip aluminized in Al or Al-1at%Si baths, and corroded in Ar/1%SO2 gas at 700-800 °C for up to 50 h. The aluminized layers consisted of not only an outer Al(Fe) topcoat that had interdispersed needle-like Al3Fe particles but also an inner Al-Fe alloy layer that consisted of an outer Al3Fe layer and an inner Al5Fe2 layer. The Si addition in the bath made the Al(Fe) topcoat thin and nonuniform, smoothened the tongue-like interface between the Al-Fe alloy layer and the substrate, and increased the microhardness of the aluminized layer. The aluminized steels exhibited good corrosion resistance by forming thin α-Al2O3 scales, along with a minor amount of iron oxides on the surface. The interdiffusion that occurred during heating made the aluminized layer thick and diffuse, resulting in the formation of Al5Fe2, AlFe and AlFe3 layers. It also smoothened the tongue-like interface, and decreased the microhardness of the aluminized layer. The non-aluminized steel formed thick, nonadherent, nonprotective (Fe3O4, FeS)-mixed scales.

High Temperature Corrosion of Al Hot-Dipped Low Carbon Steels in N<sub>2</sub>/H<sub>2</sub>S-Mixed Gases

A low carbon steel was hot-dip aluminized, and corroded in the N2/0.4%H2S-mixed gas at 650-850°C for 20-50 h in order to find the effect of aluminizing on the high-temperature corrosion of the low carbon steel in the H2S environment. A thin Al topcoat and a thick Al-Fe alloy layer that consisted primarily of Al5Fe2 and some FeAl and Al3Fe formed on the surface after aluminizing. The corrosion rate increased with an increase in temperature. Hot-dip aluminizing increased the corrosion resistance of the carbon steel through forming a thin protective α-Al2O3 scale on the surface. The α-Al2O3 scale was susceptible to spallation. During corrosion, internal voids formed in the Al-Fe alloy layer, where the Al5Fe2, AlFe, and Al3Fe compounds gradually transformed through interdiffusion.

Effect of Al Hot-Dipping on High-Temperature Corrosion of Carbon Steel in N2/0.1% H2S Gas

High-temperature corrosion of carbon steel in N2/0.1% H2S mixed gas at 600–800 °C for 50–100 h was studied after hot-dipping in the aluminum molten bath. Hot-dipping resulted in the formation of the Al topcoat and the Al-Fe alloy layer firmly adhered on the substrate. The Al-Fe alloy layer consisted primarily of a wide, tongue-like Al5Fe2 layer and narrow Al3Fe layer. When corroded at 800 °C for 100 h, the Al topcoat partially oxidized to the protective but non-adherent α-Al2O3 layer, and the interdiffusion converted the Al-Fe alloy layer to an (Al13Fe4, AlFe3)-mixed layer. The interdiffusion also lowered the microhardness of the hot-dipped steel. The α-Al2O3 layer formed on the hot-dipped steel protected the carbon steel against corrosion. Without the Al hot-dipping, the carbon steel failed by forming a thick, fragile, and non-protective FeS scale.

Aluminizing and Corrosion of Carbon Steels in N2/0.5%H2S Gas at 650-850℃

The effect of hot-dip aluminizing on the corrosion of the low carbon steel was studied at <TEX>$650-850^{\circ}C$</TEX> for 20-50 h in <TEX>$N_2/0.5%\;H_2S$</TEX> gas. The aluminized steel consisted primarily of the Al topcoat and the underlying Al-Fe alloy layer. Aluminizing drastically improved the corrosion resistance by forming the <TEX>${\alpha}-Al_2O_3$</TEX> surface scale. Without aluminizing, the steel formed nonadherent, fragile, thick scales, which consisted of FeS as the major phase and iron oxides such as FeO, <TEX>$Fe_3O_4$</TEX> and <TEX>$Fe_2O_3$</TEX> as minor ones.

Effect of Ti on the growth of the Fe–Al layer in a hot dipped Zn–6Al–3Mg coating

This present study discusses the effect of Ti addition to a Zn–6Al–3Mg galvanizing bath on the growth of an Fe–Al alloy layer. When the Ti content in a Zn–6Al–3Mg bath is less than 0.052wt.%, a subsequent increase of Ti in the bath causes a reduction in the average thickness of the resulting FeAl3Znx layer and the Fe2Al5Znx layer. The restraining effect of Ti on the growth of the Fe2Al5Znx layer is attributed to the occupation of Ti atoms in vacancies within the Fe2Al5Znx phase. The average thickness of the FeAl3Znx and Fe2Al5Znx layers increases significantly when the Ti content exceeds 0.052wt.%. The linear growth of the FeAl3Znx layer suggests that an interfacial reaction controls the growth process. The growth curve of the Fe2Al5Znx layer is parabolic, implying that its growth is controlled by the diffusion of Fe atoms. The effect of Ti on the growth of the Fe–Al alloy layer in the Zn–6Al–3Mg bath with different amounts of Ti has been explained based on different mechanisms.

Growth of Fe&lt;sub&gt;2&lt;/sub&gt;Al&lt;sub&gt;5&lt;/sub&gt; Phase on Pure Iron Hot-Dipped in Al–Mg–Si Alloy Melt with Fe in Solution

We have examined the growth and morphology of the Fe–Al alloy layer (Fe2Al5-η and FeAl3-θ phases) on pure Fe sheets hot-dipped at 750°C in an Al-8.2Mg-4.8Si–Fe (wt.%) and Al–Fe alloy melts which are saturated with Fe where the effect of Fe dissolution from the solid Fe can be eliminated. In both the Al–Mg–Si–Fe and Al–Fe melts, the total thickness of Fe sheets increased during the dipping, indicating that the diffusion of Al from the melt side is dominant in the growth of the Fe–Al alloy layer. The growth rate constant of the η phase layer in the both melts was close to 0.5 while the growth rate in the Al–Mg–Si–Fe alloy melt was approximately one order of magnitude slower than that in the Al-Fe melt. The θ phase layer appeared continuous in the Al–Mg–Si–Fe alloy melt, whereas the layer was discontinuous in the Al–Fe melt. The sluggish growth of the η phase layer in the Al–Mg–Si–Fe alloy melt is discussed.

Microstructure and Erosion Resistance of Hot-Dip-Aluminized 3Cr13 Steel

Fe-Al intermetallic coating was prepared on 3Cr13 steel by hot-dip aluminizing and diffusion process. The morphology and phase of the coating were analyzed; the erosion behavior of hot-dip-aluminized 3Cr13 steel was investigated. Results showed that the thickness of the coating increased with diffusion temperature, but decreased when diffusion temperature exceeded 800°C. The Fe-Al alloy layer diffused at 900°C presented compacted microstructure, and mainly contained FeAl and a few Fe3Al. Fe-Al intermetallic coating possessed obviously declined erosion loss compared with unaluminized 3Cr13 steel and represented typical erosion characteristics of ductile material.

Structure and Performance of Fe-Al Alloy Layer for Twin Wire Surfacing on the Steel Substrate

Surfacing of Fe-Al alloy layer is achieved on the surface of Q235 steel plate by using the twin wire consisting of one aluminum welding wire and one steel welding wire in the shielding of pure argon. When the ER1100 aluminum welding wire of Φ1.6mm and ER50-6 steel welding wire of Φ1.2mm are selected as the master wire and slave wire respectively, with preheating and interlayer temperature reaching 350°C by controlling filling volume of aluminum and steel , the Fe-Al alloy layer featured by well-formed welding line is thus gained with no macroscopic defect. As the mechanical performance testing shows, the shear strength of surface combining surfacing layer and steel substrate is higher than 270MPa. The rupture position is located in surfacing layer and it turns out to be brittle fracture; the micro-hardness of surfacing layer ranges from 320HV to 420HV. Abrasion resistance testing indicates that abrasion resistance of surfacing layer is better than that of base material. According to micro-structure observation, the welding line is a coarsening columnar structure with a great deal of precipitated phase. According to EDAX, the aluminum content of precipitated phase in surfacing layer ranges from 24% to 32% (at), and the steel content ranging from 76% to 68% (at) - it is thus considered a Fe3Al structure through XRD.

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.

Effects of Heat Treatment Conditions on Formation of Fe-Al Alloy Layer during High Temperature Aluminizing

Diffusion couples of Fe 2 Al 5 and various substrates with different carbon content, pure iron, 0.27 mass% C steel and 0.45 mass% C steel were processed, and the formation of an Fe-Al alloy layer in the temperature range from 750 to 1 000°C was investigated. FeAl 2 , FeAl, and aluminum solid solution (αFe(Al)) were confirmed in the alloy layer formed by heating the diffusion couples. Voids were generated inside the Fe 2 Al 5 layer and near the interface between the FeAl layer and αFe(Al) layer. The layer growth of FeAl and αFe(Al) obeyed the parabolic law of the diffusion time, t 1/2 . However, the thickness of FeAl saturated over a diffusion time longer than 3.6 ks at 950°C because of the concentration of voids at the FeAl layer/αFe(Al) layer interface and the disappearance of the Fe 2 Al 5 layer. The activation energy for the formation of the FeAl layer in all kinds of the substrates was approximately 200 kJ/mol in the whole temperature range and the substrate. On the other hand, the activation energies for the αFe(Al) layer in the 0.27 mass% C steel and the 0.45 mass% C steel were larger than that in pure iron at 750-800°C.

Phase Structure Of Fe-Al Alloy Layer On The Surface Of A New Aluminized Steel

Phase Structure Of Fe-Al Alloy Layer On The Surface Of A New Aluminized Steel

X-ray diffraction and TEM analysis of Fe–Al alloy layer in coating of new hot dip aluminised steel

The phase structure in the Fe-Al alloy layer of a new hot dip aluminised steel has been researched by means of electron probe microanalysis, X-ray diffraction and TEM, etc. The test results indicated that the Fe-Al alloy layer of the new aluminised steel was composed of Fe3Al, FeAl, a few Fe2Al5 and α-Fe (Al) solid solution. There was no brittle phase containing higher aluminium content, such as FeAl3 (59.18 wt-%Al) and Fe2Al7 (62.93 wt-%Al). The tiny cracks and brittlement, formerly caused by these brittle phases in the conventional aluminium coated steel, were effectively eliminated. There was no microscopic defect (such as tiny cracks, pores or loose) in the coating. This is favourable for resisting high temperature oxidation and corrosion of the aluminised steel.

Fine structures in Fe3Al alloy layer of a new hot dip aluminized steel

The fine structure in the Fe-Al alloy layer of a new hot dip aluminized steel (HDA) was examined by means of X-ray diffractometry (XRD), electron diffraction technique, etc. The test results indicated that the Fe-Al alloy layer of the new aluminized steel mainly composed of Fe3Al, FeAl and α-Fe (Al) solid solution. There was no brittle phase containing higher aluminum content, such as FeAl3 (59.18% Al) and Fe2Al7 (62–93% Al). The tiny cracks and embrittlement, formerly caused by these brittle phases in the conventional aluminum-coated steel, were effectively eliminated. There was no microscopic defect (such as tiny cracks, pores or loose layer) in the coating. This is favourable to resist high temperature oxidation and corrosion of the aluminized steel.

鉄-アルミニウム合金層を介した鉄と固体亜鉛との反応

鉄-アルミニウム合金層を介した鉄と固体亜鉛との反応