Hot-Dip Aluminizing of Low Carbon Steel Using Al-7Si-2Cu Alloy Baths (original) (raw)
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Formation Behavior of an Intermetallic Compound Layer during the Hot Dip Aluminizing of Cast Iron
ISIJ International, 2012
Hot dip aluminizing (HDA) is an effective way to improve the high temperature corrosion resistance and scaling resistance of ferrous materials. The formation of intermetallic compound layers between the two materials is a dominant factor in determining the properties of hot dip aluminized steel. The formation behavior of the intermetallic compound layer between a Si alloyed Al melt and cast iron has been investigated. The thickness of the intermetallic compound layer was significantly reduced as a result of the increased carbon content of the cast iron matrix. The thickness of the intermetallic compound layer formed in the Al-Si-Fe three-component alloy system remains constant in the early stage of the reaction, and it becomes increasingly rough with increased reaction time. The increased roughness could be attributed to the increased Fe concentration in the Al-Si melt near the cast iron surface, which is a result of the increased inter-diffusion of Al, Si and Fe atoms with increased reaction time by which the formation, melting and spallation of the intermetallic compound layer is enhanced.
The morphology of coating/substrate interface in hot-dip-aluminized steels
Materials Science and Engineering: A, 2008
In hot-dip-aluminized (HAD) steels, the morphology and the profile of the interface between the aluminum coating and the substrate steel, are affected both by the composition of the molten aluminum as well as by the composition, and even the microstructure, of the substrate steel. This effect has been investigated using optical and scanning electron microscopy, and X-ray diffraction. The reaction between the steel and the molten aluminum leads to the formation of Fe-Al inter-metallic compounds on the steel surface. The thickness of the inter-metallic compound layer as well as the morphology of the interface between the steel and the interlayer varies with the silicon content of the molten aluminum. In hot-dip-aluminizing with pure aluminum, the interlayer is 'thick' and exhibits a finger-like growth into the steel. With a gradually increasing addition of silicon into the aluminum melt, the thickness of the interlayer decreases while the interface between the interlayer and the substrate gradually becomes 'smoother'. With an increase in the carbon content of the substrate steel the growth of the interlayer into the steel is impeded by the pearlite phase, whereas the ferrite phase appears to dissolve more readily. X-ray diffraction and electron microscopic studies showed that the interlayer formed in samples aluminized in pure aluminum, essentially consisted of orthorhombic Fe 2 Al 5. It was further observed that the finger-like grains of Fe 2 Al 5 phase exhibited a preferred lattice orientation. With a gradual addition of silicon into the aluminum melt, a cubic phase based on Fe 3 Al also started to form in the interlayer and replaced most of the Fe 2 Al 5 .
Heat treatment was introduced onto the aluminum coated low carbon steel to promote the formation of thin layer of oxide for enhancement of oxidation protection of steel. This process has transformed the existing intermetallic layer formed during hot dip aluminizing process. Experiment was conducted on the low carbon steel substrates with 10mm x 10mm x 2mm dimension. Hot dip aluminizing of low carbon steel was carried out at 750 ºC dipping temperature in a molten pure aluminum for 5 minutes. Aluminized samples were heat treated at 600 ºC, 700 ºC, 800 ºC, and 900 ºC for 1 hour. X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and EDAX were used in investigation. From the observation, it showed the intermetallic thickness increased with the increase in temperature. The result of EDAX analysis revealed the existence of oxide phase and the intermetallics. The XRD identified the intermetallics as Fe2Al5 and FeAl3. ABSTRAK Rawatan haba telah diperkenalkan ke atas aluminium bersalut keluli berkarbon rendah menggalakkan pembentukan lapisan nipis oksida untuk peningkatanperlindungan pengoksidaan keluli. Pembinaan ini telah mengubah lapisan antaralogam sedia ada membentuk semasa pencicah pedas pengaluminiuman proses.Eksperimen dijalankan di substrat keluli berkarbon rendah dengan 10mm x 10mmdimensi x 2mm. Pengaluminiuman pencicah pedas keluli berkarbon rendah telah dijalankan di 750 suhu pencelupan ºC di satu aluminium tulen lebur selama 5 minit.Contoh-contoh Aluminized ialah haba merawat di 600 ºC, 700 ºC, 800 ºC , dan 900 ºC untuk 1 jam. Belauan Sinar-x (XRD), Scanning Electron Microscope (SEM) and EDAXtelah digunakan dalam penyiasatan. Dari pemerhatian, ia menunjukkan ketebalan antara logam menambah dengan kenaikan itu dalam suhu. Keputusan analisis EDAXmendedahkan kewujudan fasa oksida dan intermetallics. XRD mengenal pastiintermetallics sebagai Fe2Al5 and FeAl3.
Properties and Growth Rate of Intermetallic Al-Fe through Hot Dipped Aluminizing
Advanced Materials Research, 2014
Hot dipped aluminizing is the one of the most famous and effective method of the surface protection. The growth behavior in the intermetallic layer by introducing a different dipping time and various of molten aluminium temperature had been detail investigated. The result showed that the top portion of the coated steel substrate is compose of a thin layer of α-Al 2 O 3 , followed by thicker Aluminium pure layer, thinner layer of FeAl 3 , and then a much thicker of Fe 2 Al 5 . The intermetallic layer is 'thick' and exhibits a finger-like growth into the steel. The thickness of Al-Fe intermetallic layer on the steel base is increased with the increasing of hot dipping temperature and time. The micro hardness testing result shown that increasing of the aluminizing temperature was increased the hardness of the intermetallic layer.
Materials Science : An Indian Journal, 2010
316L stainless steel; Aluminizing; Al-Si alloys; Intermetallic layer; Microhardness. KEYWORDS ABSTRACT 316L stainless steel was coated by hot-dipping into commercially pure Al and two Al-Si alloys of 7%Si and 11.5% Si contents at dipping time varying from 1 to 60 min and temperatures ranging from 750 to 900ºC. Moreover, 5%Fe was added to each bath at 900C. Microstructure observation, morphology of the alloy layer, element distribution, chemical composition and microhardness determination were performed by optical microscopy, scanning electron microscope (SEM) with an energy dispersive X-ray facility (EDX), and microhardness tester. The thickness of the intermetallic layer formed increases with increasing both the bath temperature and dipping time. Based on the experimental data, it is found that the largest and most uniform layer thickness was obtained at 800ºC and time 20 min in pure Al molten bath, and this is also the case when aluminizing in Al-11.5%Si molten bath, but when using Al-7%Si molten bath, the optimum dipping temperature was about 750C also at time 20 min. The existence of Si reduces the intermetallic layer thickness and increases its microhardness. The addition of 5%Fe to the melt increases the layer thickness.
Multidiszciplináris tudományok, 2021
The investigation in this paper is based on the existence of carbon content and its role in the formation of Fe-Al intermetallic layer in unalloyed carbon steel C45 with a carbon content of 0.44 wt.%. Several sophisticated techniques such as PFIB SEM equipped with EDS and EBSD, GD-OES were employed for the in-depth surface analysis. The results of the metallographic examination reveal that the carbon would appear and could be well detected at the interface between the solidified aluminum and the solid iron-base steel substrate and got also incorporated in the top aluminum layer. Furthermore, due to the dissolution and outward diffusion of iron into the liquid aluminum melt during the HDA process, plus its involvement in the formation of the solid intermetallic surface layer, thus the carbon atoms gaining higher chemical affinity there will also be more likely to form carbide precipitates of different kinds like Fe3AlC and AlC inside these developing surface layers on the C45 type st...
Morphological and microstructural studies on aluminizing coating of carbon steel
2013
Hot dip aluminizing is one of the most effective methods of surface protection for steels and is gradually gaining popularity. The morphology and microstructure of an inter-metallic layer form on the surface of low carbon steel by hot dip aluminization treatment had been studied in detail. This effect has been investigated using optical and scanning electron microscopy, and X-ray diffraction. The result shows that the reaction between the steel and the molten aluminium leads to the formation of Fe-Al inter-metallic compounds on the steel surface. X-ray diffraction and electron microscopic studies showed that a two layer coating was formed consisting of an external Al layer and a (Fe 2 Al 5 ) inter metallic on top of the substrate after hot dip aluminizing process. The inter-metallic layer is 'thick' and exhibits a fingerlike growth into the steel. Microhardness testing shown that the intermetallic layer has high hardness followed by steel substrate and the lowest hardness was Al layer
Microstructure of hot dip coated Fe–Si steels
Thin Solid Films, 2011
Hot dipping is a coating technique pre-eminently used in industry to galvanize machine parts or steel sheets for constructional applications. However, other hot dipping applications have been developed in order to have a positive effect on specific material properties. For instance, in Fe-Si electrical steels, a Si/Al rich top layer is applied and followed by diffusion annealing to increase the electrical resistivity of the material and consequently, lower the power losses. Hot dipped aluminised mild steels have been developed with increased corrosion resistance for high temperature applications by the development of a dense Al 2 O 3 layer. Regardless of the type of steel coated and the intended application, after the interaction between the molten Al and the solid material, three constituents are formed: Fe 2 Al 5 , FeAl 3 and an Al-rich alloy. The structural morphology, which can negatively affect the wear resistance and the thermal stability, also appears to be highly dependent on the chemical composition of the base material. To study thermo-mechanical and compositional effects on the coating behavior after hot dipping, cold rolling with different reductions was performed on different Fe-Si materials. It was demonstrated that hardness differences between the layers caused crack formation inside the Fe 2 Al 5 layer during subsequent deformation. The present work reports the results obtained on materials that were hot dipped in a hypo-eutectic Al + 1 wt.% Si bath. The bath was used to coat Fe-Si steel substrates with variable silicon content with dipping times ranging from 1 to 20 s. Before dipping, the samples were heated to 700°C and subsequently immersed in the liquid bath at temperatures of 710°C, 720°C and 740°C. To further evaluate the interactions between Al, Si and Fe, a diffusion annealing treatment at 1000°C was performed. The main diffusing elements during this treatment are Al and Fe, although small variations in Si content are also observed. At a certain distance from the surface, voids were observed, which most probably can be related to the Kirkendall effect. A characterization of the formed intermetallics was performed by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffraction (XRD) and Electron Backscatter diffraction (EBSD).
A low temperature aluminizing treatment of hot work tool steel
2013
Conventional aluminizing processes by pack cementation are typically carried out at elevated temperatures. A low temperature powder aluminizing technology was applied to the X40CrMoV5-1 hot tool steel. The aluminizing temperature was from 550 °C to 620 °C. Effects of temperature and time on the microstructure and phase evolution were investigated. Also, the intermetallic layer thickness was measured in the aluminized layer of a steel substrate. The cross-sectional microstructures, the aluminized layer thickness, and the oxide layer were studied. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and glow discharge optical spectroscopy (GDOS) were applied to observe the cross-sections and the distribution of elements.
Coatings
Pre-treated low carbon steel specimens with flux or flux + tin mixture were coated by hot-dip aluminizing process. Al alloy (6061) was melted and hold at 750 °C. Fluxed and pre-tinned low carbon steel samples were dipped in a molten bath for time intervals of 0.5, 1, 2.5 and 3.5 min. Applying double coating processes via tinning-aluminizing techniques facilitated the formation of Fe-Al intermetallic interface and increasing the thickness of homogenous coating layer over the substrate material. The presence of Sn facilitates to great extent the formation of a better interlayer-free bond of residual flux and/or oxides. The fluxed–dipped steel substrates have inhomogeneous distribution of Al alloy coating as well as an interface with residual flux and oxides for dipping time up to 2.5 min. A homogenous distribution with good thickness morphology of the Al alloy coating and homogeneous thin intermetallic interface was achieved for tinned steel substrate at all applied dipping times. The...