Hot-dip Aluminizing Research Articles

Study on the mechanism of aluminum melt corrosion of Fe-SG series metals

This paper investigates the corrosion behavior of Fe-SG series metals with different graphite nodule counts to molten Al by using the ultrasonic vibration hot-dip aluminum experimental method. Fe-SG series metals to aluminum melt exhibited a much better corrosion resistance compared to H13 tool steel. As the graphite nodule count increases, the hot melting loss rate of Fe-SG series metals gradually decreases, indicating an improvement in corrosion resistance to aluminum melt. Scanning and EDS analysis of the samples after hot-dip aluminum testing revealed that the thickness of the product layer increased progressively with the extension of hot-dip aluminum time. Through the analysis of the structure and composition of the product layer, it was found that the corrosion products in H13 steel were composed of Fe2Al5 and FeAl3. In addition to the two phases, the product layer of the Fe-SG series metals also contained granularly distributed Fe-Al-Si intermetallic compounds within the Fe2Al5 phase. This resulted in a better corrosion resistance to aluminum melt.

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.

Characterizing sliding wear behavior of A1100/AlFe (p) composites produced via repeated fold-forging and annealing

Abstract Aluminum matrix/aluminum-iron intermetallic composite materials pose challenges in plastic processing due to the susceptibility of hard intermetallic compound particles to fracture. This study introduces a novel fabrication method involving pure iron mesh, hot-dip aluminum plating, and solidification. Through ten consecutive folding, forging, and intermediate annealing cycles, aluminum matrix and iron undergo diffusion, leading to the formation of Fe2Al5 and FeAl3 interface reaction layers, as confirmed by X-ray diffraction analysis. Subsequent forging cycles cause the breakage or detachment of Fe2Al5 and FeAl3 particles from the interface, resulting in the formation of large-sized Fe2Al5 and small-sized Fe2Al5 intermetallic particles. FeAl3 intermetallic particles are observed via microscopic examination. These particles can be uniformly dispersed within the aluminum matrix through plastic flow, enabling the successful fabrication of A1100/Fe2Al5 and AlFe3 composite sheets. Furthermore, the study investigates the impact of intermetallic compound content, sliding speed, and forward load on the dry sliding wear of A1100/FeAl composites. It is found that Fe2Al5 and AlFe3 intermetallic compound particles effectively mitigate adhesive wear, plowing, and oxidative wear of the composites. With an AlFe intermetallic compound content of 4.3 wt.%, the volume wear rate remains low under conditions corresponding to PV = 56.652 (equivalent to a normal load of 19.6 kPa and a sliding speed of 2.87 m s−1).

Molten Aluminum-Induced Corrosion and Wear-Resistance Properties of ZrB2-Based Cermets Improved by Sintering-Temperature Manipulation.

During the hot dip aluminum plating process, components such as sinking rollers, pulling rollers, and guide plates will come into long-term contact with high-temperature liquid aluminum and be corroded by the aluminum liquid, greatly reducing their service life. Therefore, the development of a material with excellent corrosion resistance to molten aluminum is used to prepare parts for the dipping and plating equipment and protect the equipment from erosion, which can effectively improve the production efficiency of the factory and strengthen the quality of aluminum-plated materials, which is of great significance for the growth of corporate profits. With AlFeNiCoCr as the binder phase and ZrB2 as the hard phase, ZrB2-based ceramic composites were prepared by spark plasma sintering (SPS). SEM, EDS and XRD were used to characterize the microstructure and properties of the sintered, corroded, and abraded material samples. The density, fracture toughness, corrosion rate and wear amount of the composite material were measured. The results show that ZrB2-AlFeNiCoCr ceramics have compact structure and excellent mechanical properties, and the density, hardness and fracture toughness of ZrB2-AlFeNiCoCr increase with the increase in sintering temperature. However, when the composite material is at 1600 °C, the relative density of the sintering at 1600 °C decreases due to the overflow of the bonding phase. Therefore, when the sintering temperature is 1500 °C, the high entropy alloy has the best performance. The average corrosion rate of ZrB2-1500 at 700 °C liquid aluminum is 1.225 × 10-3 mm/h, and the wear amount in the friction and wear test is 0.104 mm3.

Effect of hot isostatic pressing on microstructure and properties of cooled hot dip aluminum coating in magnetic field

The effect of hot isostatic pressing (HIP) on the microstructure and properties of hot dip aluminum coating cooled in a magnetic field was investigated in this study. In order to improve the microstructure and properties of magnetic dip aluminum coating, hot isostatic pressing technology was used for post-treatment. Initially, a traditional aluminum-impregnated coating was prepared on the surface of titanium alloy TA15, an alternating electromagnetic field was applied during the forming and solidification process of the coating. Finally, the coating was treated with hot isostatic pressing technology. Analyzed three different coatings of the microstructure and element distribution, and tested the microhardness of the coatings at various positions. The test results revealed that the TA15 titanium alloy hot-dip aluminum coatings obtained through the three different processes exhibited a gradient structure. Compared with the traditional hot-dipped aluminum air-cooled coating, when an appropriate intensity of alternating electromagnetic field was applied during the coating solidification process, the outer coating structure was enhanced, the number of holes was reduced, the microstructure density increased, and the number of cracks significantly decreased. The defects of the 800 °C hot isostatic magnetic cold and hot dip aluminum coating were repaired under high temperature and pressure, resulting in a uniform and fine microstructure. The comprehensive properties of the magnetic cold and hot dip aluminum coating on the surface of the titanium alloy were effectively enhanced through hot isostatic pressing.

Spontaneous growth of Sn whisker on the hot-dipping Al[sbnd]Sn alloy coating on Fe-Cr-B cast steel

Although the MAX phase solid solutions and spontaneous growth of Sn whiskers had been reported widely, the study on the spontaneous growth of whisker at room temperature on the MAB phase was very rare. In our previous work, the periodic layered structure consisted of alternatively arranged Cr-Al-B MAB phase and FeAl3 was formed during the hot-dip aluminizing of Fe-Cr-B cast steel. Herein, the Cr-(Al, Sn)-B MAB phase solid solution was prepared by HDA of Fe-Cr-B cast steel in a AlSn alloy melt and subsequently thermal diffusion treatment. Sn atoms in the Al melt could partially occupy the positions of Al atoms in the Cr-Al-B MAB phase by A-site replacement approach, which resulted in the formation of the Cr-(Al, Sn)-B MAB phase solid solution. Subsequently, spontaneous growth of β-Sn whisker occurred on the Cr-(Al, Sn)-B MAB phase solid solution at room temperature. The original Sn source was the pure Sn phase among the grains of Cr-(Al, Sn)-B MAB phase solid solution. The mass transport pathway for maintaining the spontaneous growth of Sn whiskers was: pure Sn among the grains of Cr-Al-B MAB phase→ Cr-(Al, Sn)-B MAB phase→ SnO2 → Sn whisker. The spontaneous growth of Sn whisker in the air resulted in the deep grooves covered on the surface of whisker, while, growth in the vacuum resulted in the prism structure at the bottom of whisker. The spontaneous growth of Sn whisker could grow from both the bottom and the tip. The findings will expand the family of MAB phase and help well understand the growth mechanism of Sn whisker.

Formation and Evolution of Interfacial Structure in Al–Si–Mg/Stainless Steel Bimetals during Hot-Dipping Process

Understanding trends in the formation of the intermetallic compound (IMC) layer in Al/Fe bimetallic composites can aid in significantly improving their mechanical properties. However, it is currently challenging to predict IMC layer formation during hot-dip aluminizing. Furthermore, the results from previous studies are difficult to compare owing to the variation in the process parameters used. Therefore, to understand how temperatures and holding times affect the thickness and hardness properties of IMC layers, we investigated the interfacial properties of aluminized stainless steel in molten Al-Si-Mg. AISI 420 stainless steel was hot-dip aluminized in an Al–Si–Mg alloy melt for 10–120 min at four different temperatures: 700, 750, 800, and 850 °C. Morphology, type, and element distribution of the phases formed in the reaction layer and the reduction rate of the aluminizing process were studied. Notably, while the reaction layer thickness increased with increasing aluminizing temperature when the holding time was low, long-term reaction caused the reaction layer to become thicker at lower temperatures. The mechanism of this morphological transformation is discussed. The results demonstrated effective trends in controlling the morphology of the intermetallic compound layer with respect to various hot-dip Al plating process parameters.

Effects of Annealing and Oxidation on the Microstructure of Hot-Dipped Aluminum–Silicon Coating of 316L Stainless Steel

Effects of Annealing and Oxidation on the Microstructure of Hot-Dipped Aluminum–Silicon Coating of 316L Stainless Steel

Hot-dip aluminizing of Fe–Cr–B cast steel in Al–Ti–B alloy melt

The periodic layered structure (PLS) composed of alternative arrangement of Cr–Al–B MAB phase and FeAl3 was formed at the (Cr, Fe)2B/Al interface during hot-dip aluminizing (HDA) of Fe–Cr–B cast steel in molten Al. However, the effect of alloying element in the Al melt on the PLS was still unknown. This work focused on the effect of Ti on the interfacial reaction between Fe–Cr–B cast steel and molten Al–Ti–B alloy. The Ti atoms in Al–Ti–B alloy melt could partially replace the Cr atoms in the M-sites of the Cr–Al–B MAB phase contained in the PLS after it formed in-situ, leading to the formation of (Cr, Ti)–Al–B MAB phase solid solution. The B atoms in the melt absorbed by the Cr–Al–B MAB phase also accounted for the blackening of the Cr–Al–B MAB phase. It was the first time that the M-site MAB phase solid solution in the Cr–Al–B system was prepared by hot-dip aluminizing.

Aluminizing of the EP33 alloy by hot-dipping

The features of hot-dip aluminizing of the EP33 alloy were studied and the structure transformation of the resulting coating during high-temperature treatment was investigated. Aluminizing the EP33 alloy leads to the formation of a continuous 120 μm thick coating, consisting of an aluminum matrix with the Cr2Al13 intermetallic compound inclusions and a continuous layer of FeAl3 intermetallic compound along the boundary with the substrate. Heat treatment of the aluminized alloy at 1100 °C ensures the formation of a layered coating structure. The phase composition of the coating from the surface to the substrate changes in the following sequence: FeAl(Ni,Cr,Ti,Mo) → FeAl(Ni,Cr,Ti,Mo)+Ni(Fe,Cr,Al,Ti,Mo) → FeAl(Ni,Cr,Ti,Mo)+Fe(Al,Ni,Cr,Ti,Mo).

Hot-Dip Aluminizing of Flow-formed AISI 4140 Steel

Cold plastic deformations recognizably cause increasing lattice imperfections such as point defects and dislocations in the structure, which could then have an effect on diffusion characteristics of the material. In order to explore such an effect of flow forming, a flow formed AISI 4140 steel and an annealed 4140 steel were subjected to the HDA process in a molten Al7020 bath at 750◦C for 4 min, and a subsequent diffusion annealing was performed at 800◦C, and their coating characteristics such as coating thickness and hardness were compared. The results indicated that the coating thickness of the flow formed samples was higher (80◦m) than that of the annealed sample (50◦m) after the HDA process. Diffusion annealing increased the coating thickness of both samples five times, reaching 400◦m and 250◦m for the flow formed and the annealed samples, respectively. Comparing the measured thickness of the coatings revealed that flow forming accelerates diffusion during the HDA process, probably due to the defect structure induced by the flow forming. On the other hand, the coating hardness was in between 1000-1100 HV for both samples, implying that the initial condition of the sample does not have a remarkable effect on hardness after the HDA process.

On the effect of thermal diffusion treatment on the hot-dipped Al-Si alloy coating on Fe-Cr-B cast steel

The periodic layered structures (PLSs) consisting of alternatively arranged Cr-Al-B MAB phase and FeAl3 were formed in-situ at the (Cr, Fe)2B/pure Al melt interface during hot dip aluminizing (HDA) of Fe-Cr-B cast steel. In the present investigation, HDA of a novel Fe-Cr-B cast steel was carried out in an Al-5.7 wt% Si alloy melt at 750 ℃ for 30 min. The HDA samples were given thermal diffusion treatment (TDT) at 750 ℃. The microstructural evolution of the Al-Si coating during HDA and TDT were analyzed in details. Results showed that Si in Al melt had a great influence on the compositions of PLSs. During HDA, Si atoms in the melt partially replaced Al atoms in the Cr-Al-B MAB phase, and Si-rich phase were rich at the boundary of Cr-Al-B MAB phase. While, during TDT, the Si-rich phase dissolved into the adjacent FeAl3. The formation process of PLSs during TDT experienced the both transformation from the laminar structure formed in the initial stage to the graininess structure at last and from disordered to ordered arrangement.

Morphology, phase composition, surface roughness evolution and growth mechanism of hot-dip aluminum coating on Mo substrate

The Al-rich hot-dip aluminum composite coatings were synthesized on Mo surface by hot-dip aluminizing under different deposition processes. The aluminide coatings present a very smooth dense coating structure with a lower surface roughness and fine grain size, the average surface roughness (RSa) values are only 0.118–0.869 μm, and the corresponding surface area growth rate (Sdr) values are 3.85–80.19 %. Increasing the deposition temperature is beneficial for the transition of low melting point compounds of the coating surface to high melting point compounds, and extending the hot dip time is profit for the diffusion and enrichment of Al atoms on the coating surface. Besides, increasing the deposition temperature or time can also promote the growth of Al4Mo grains, thereby significantly increasing the coating thickness. When the deposition temperature is 750 °C, the thicknesses of Al4Mo and Al8Mo3 layers increases in a parabolic law with deposition time, and the Kp values both of them are 3.46 × 10−13 m2/s and 1.47 × 10−15 m2/s, respectively. The growth of the coating depends on the continuous diffusion of Al atoms towards the substrate direction, and the difference in chemical potential between Al atoms in each phase is the main driving force for coating growth.

Effect of reaction temperature and holding time on the interfacial microstructure of Al–Si–Mg/Cu bimetals manufactured by hot-dip aluminizing

This study investigates the effects of reaction temperature and holding time on intermetallic compounds (IMCs) at the Al–Si–Mg/Cu bimetals interface fabricated by hot-dip aluminizing. Previous research has demonstrated that the presence of IMC layers in Al–Si–Mg/Cu bimetals significantly increased the interface hardness. This study aims to achieve a continuous change in hardness at the interface by forming Cu3Al layers, thus exhibiting the lowest hardness and highest ductility among the Al–Cu IMCs. The thickness and morphology of the Al–Cu IMC layer depend on the reaction temperature and holding time. Al–Cu intermetallic phases with higher Cu contents, such as Cu3Al, Cu9Al4, Cu3Al2, CuAl, and CuAl2, were closer to the Cu surface. The formation of Cu3Al leads to continuous changes in the hardness of the Cu and IMC layers. Furthermore, the growth kinetics of IMCs and their formation mechanisms are discussed. The results indicate that hot-dip aluminizing is an effective method for controlling the composition and thickness of the IMC layer to achieve a continuous change in the interfacial hardness.

Effect of Si Content on Microstructures and Electrochemical Properties of Al-xSi-3.5Fe Coating Alloy

Hot-dip aluminum alloy is widely used in the engineering fields. However, during the aluminum plating process, Fe inevitably enters and reaches a saturation state, which has a significant impact on the corrosion resistance and microstructure of the coating. Currently, adding Si during the hot-dip aluminum process can effectively improve the quality of the coating and inhibit the Fe-Al reaction. To understand the effect of Si content on the microstructure and electrochemical performance of Al-xSi-3.5Fe coating alloys, the microstructure and post-corrosion morphology of the alloys were analyzed using SEM (Scanning Electron Microscope) and XRD (X-ray Diffraction). Through electrochemical tests and complete immersion corrosion experiments, the corrosion resistance of the coating alloys in 3.5 wt.% NaCl was tested and analyzed. The results show that the Al-3.5Fe coating alloy mainly comprises α-Al, Al3Fe, and Al6Fe. With the increase in Si addition, the iron-rich phase changes from Al3Fe and Al6Fe to Al8Fe2Si. When the Si content reaches 4 wt.%, the iron-rich phase is Al9Fe2Si2, and the excess Si forms the eutectic Si phase with the aluminum matrix. Through SKPFM (Scanning Kelvin Probe Force Microscopy) testing, it was determined that the electrode potentials of the alloy phases Al3Fe, Al6Fe, Al8Fe2Si, Al9Fe2Si2, and eutectic Si phase were higher than that of α-Al, acting as cathode phases to the micro-galvanic cell with the aluminum matrix, and the corrosion form of alloys was mainly galvanic corrosion. With the addition of silicon, the electrode potential of the alloy increased first and then decreased, and the corrosion resistance results were synchronous with it. When the Si content is 10 wt.%, the alloy has the lowest electrode potential and the highest electrochemical activity.

Damage cause analysis of coating failure of pot roll for hot-dip aluminizing

Hot-dip aluminized steel is produced by immersing cold-rolled steel in a molten aluminum bath for a certain period. However, the pot rolls immersed in the aluminum bath suffer significant surface damage due to the reactions with the molten bath. This study identified the cause of surface damage of the stabilizer roll used for continuous hot-dip plating of aluminum at 660 °C. The damage was caused by molten Al infiltrating a defective structure with interconnected pores and splat boundaries. This molten Al dissolves the metal components of both the coating and substrate. As the lower part of the coating melts and liquefies, repetitive external frictional forces lead to the formation and growth of cracks in the upper coating. That eventually leads to the upper part of the coating partially or entirely detaching, resulting in surface defects in the form of pits. Possible ways to extend the lifetime of the port rolls to suppress such damage have been proposed.

Influence of calcium on the morphology and corrosion performance of hot-dip Al–Si coatings

Hot-dip aluminizing coatings are gaining attention owing to their corrosion resistance under harsh conditions and economic viability. Although Ca incorporation into metal alloy coatings has been demonstrated to improve the corrosion resistance, Ca addition to hot-dip aluminizing coatings is yet to be reported. Here, we investigated the effect of the Ca content on the microstructures and electrochemical properties of hot-dip aluminizing coatings on commercial quality steel. Defect-free coatings were obtained by optimizing the hot-dipping parameters. Ca promoted the precipitation of CaAl2Si2, altering the morphology of the coating and improving the corrosion resistance. However, owing to the limited stability of the passive layer, the inclusion of Ca did not significantly affect the long-term corrosion characteristics of the Al alloy coating.

Kinetics of intermetallic compound layers between AISI 321 stainless steel and molten aluminum

The interfacial reaction between liquid aluminum and solid steel is critical to understanding the evolution of intermetallic compounds (IMCs) in the brazing and weld brazing processes of aluminum-to-steel dissimilar alloys. In this study, hot dip aluminizing of AISI 321 stainless steel at different temperatures was conducted to reveal the influence of reaction temperature and time on interfacial IMCs. Electron microscopy analyses were employed to investigate the interfacial microstructures. A single layer of θ-Fe4Al13 was observed at 700°C. In contrast, the IMCs of interfaces dipped at 800–1000°C consisted of a thin inner layer of η-Fe2Al5 + ζ-FeAl2 next to the steel and a thick layer of θ-Fe4Al13 close to the aluminum. For the inner layer, the thickness increased with increasing dipping temperature and time. Its growth was described by a parabolic rate law, which suggested a diffusion-controlled mechanism at the interface. An activation energy of 66.5 kJ mol−1 was obtained. For the Fe4Al13 layer, the thickness evolution at different temperatures was different from that of the inner layer, with a thick IMC layer at 700°C, a thinner IMC layer at intermediate temperatures (from 800 to 900°C), and a slightly thicker IMC layer from 950 to 1000°C. The growth kinetics of Fe4Al13 at 700°C were controlled by diffusion, interfacial reactions, and dissolution mechanisms. The evolution of Fe4Al13 between 800 and 1000°C was governed by diffusion and dissolution mechanisms. The appearance of the inner layer and the evolution kinetics of Fe4Al13 accounted for the decrease in thickness with increasing temperature between 700 and 900°C.

A Study on the High-Temperature Molten Salt Corrosion Resistance of Hot-Dip Aluminum/Carburizing Composite Coating on Ti65 Titanium Alloy

This article presents a new method for preparing a coating on Ti65 titanium alloy using a two-step procedure comprising hot-dipped aluminum and solid carburization. The effects of the carburization on the hot-dipped aluminum coating against the presence of a NaCl deposit at 810 °C were systematically studied. In this article, the microstructure, morphology, phase composition of the coating, and corrosion products were investigated using SEM (Scanning Electron Microscopy), EDS (Energy Dispersive Spectrometer), and X-ray diffraction. The results indicated that the corrosion resistance of the hot-dip aluminum/carburizing composite coating was not significantly enhanced with the hot-dip aluminum coating. This can be attributed to the formation of TiC and Ti3AlC after carburization, which promoted the formation of loose and unprotected TiO2 in the coating during molten salt corrosion. In addition, the oxidation of the carbon atom into CO2 led to a high concentration of pores in the coating, creating channels for NaCl to penetrate the coating and accelerate the corrosion rate.

Effects of Zn and Si on the microstructure evolution of the Cr-Al-B MAB phase contained in the periodic layered structure formed in-situ

The MAB phases gain large attention in today's world because of their combination of metallic and ceramic. In our previous work, the periodic layered structures (PLSs) containing Cr-Al-B MAB phase were formed at the Fe-Cr-B cast steel/molten Al interface. This work reports the preparation method of the new A-site alloyed Cr-Al-B MAB phase through hot-dip aluminizing (HDA) in different Al melts and subsequent thermal diffusion treatment (TDT) of Fe-Cr-B cast steel. It was found that the Zn and Si in the Al melts had great effects on the formation and microstructure evolution of the Cr-Al-B MAB phase formed during HDA and TDT. Both Zn and Si could partially replace the Al atoms in Cr-Al-B MAB phase, leading to forming a solid solution with double A atoms. The Cr-(Al, Zn)-B and Cr-(Al, Si)-B MAB phases were achieved by A-site replacement in Cr-Al-B MAB phase. Meanwhile, Zn thickened the thickness of this MAB phase, while, Si decreased that of the MAB phase. However, when they were dopped simultaneously, Zn atom preferentially replaced Al atom in Cr-Al-B MAB phase with that of the substitution of Si not happening.