Fe-Zn Intermetallic Compounds Research Articles

Influence of phosphorus on the growth of Fe–Zn intermetallic compound in Zn/Fe diffusion couples

Zn/Fe and Zn/Fe–P liquid–solid diffusion couples were annealed at 450°C to investigate the effect of phosphorus in steel on the growth kinetics of Fe–Zn intermetallic compounds in diffusion zone. The results show that phosphorus in steel can delay or suppress the growth of Г phase and promote the growth of ζ phase. The higher the content of phosphorus in steel is, the faster the growth of the ζ phase is. The growth kinetics of the total layer of Fe–Zn intermediate phases in Zn/Fe–0.123wt.%P diffusion couple is the same as that in Zn/Fe diffusion couple. But the growth behavior of Fe–Zn intermediate phases in Zn/Fe–0.340wt.%P diffusion couple differs remarkably from that in Zn/Fe diffusion couple. The diffusion path model is introduced to explain this phenomenon.

Phase Relationships in the Zn-Rich Corner of the Zn-Fe-Zr System

The phase relationships in the Zn-rich corner of the Zn-Fe-Zr system at 450, 600 and 800 °C were investigated by means of x-ray powder diffraction (XRD) and scanning electron microscopy coupled with energy/wave dispersive spectroscopy (SEM-EDS/WDS). Two ternary compounds were found in the system. One of them was designated as ZrFe2Zn20 according its narrow composition range. It is a CeCr2Al20-type compound with lattice parameter a = 1.3941 nm. ZrFe2Zn20 is stable below 878.6 °C and can co-exist with all binary compounds in the Zn rich corner of the system. The other one was designated as Zr2Fe3Zn5. SEM-WDS analysis indicated that Fe was hardly detected in ZrZn22, Zr5Zn39 and ZrZn3. And no Zr was dissolved in all Fe-Zn intermetallic compounds.

Whisker growth from an electroplated zinc coating

The formation of Zn whiskers threatens the reliable operation of electronic equipment with an electrical shorting hazard. As with tin whiskers (much more intensively researched than Zn whiskers), the mechanism of formation is still not clear. This work investigated the Zn whisker growth mechanism for an electroplated Zn coating above a carbon steel substrate from a raised floor tile. Iron–zinc (Fe–Zn) intermetallic and Zn oxides were identified by x-ray diffraction analysis (XRD) and electron probe microanalysis (EPMA). Fe–Zn intermetallic compounds formed on the surface of the Zn layer in addition to the interface between the Zn coating and the steel substrate. Zn oxides formed primarily on the surface of the Zn coating. Fe–Zn intermetallic compounds and Zn oxide formation can be the source of a residual stress that promotes Zn diffusion to the surface of electroplated Zn coating, resulting in the formation of Zn whiskers.

Microstructure of the coating and mechanical properties of galvanized chromium-rich martensitic steel

Protecting the modern high-strength steels against corrosion is a challenge because the coating technology must be compatible with forming and must preserve the mechanical performances. Batch galvanizing after hot stamping could provide a simple solution to this complex problem. A commercial high-strength martensitic steel containing 13wt.% Cr, 0.35wt.% Si, 0.3wt.% Mn and 0.15wt.% carbon has been galvanized with a commercial zinc alloy. Galvanizing produces a ~15μm thick coating that is bright, continuous and metallurgically bonded. The intermetallic layer is made of ς crystals, which forms an open 3-dimensional structure. Tin, nickel and aluminium are found able to moderate the Sandelin effect. Comparison with other steels galvanized the same way indicates that chromium slows down the kinetics of the metallurgical reaction. Chromium distributes both in the ς and η phases, and follows a diffusion-like profile in the coating. The nickel from the alloy concentrates in the Fe–Zn intermetallic compound. Aluminium segregates at the surface and interface. It also provides a gettering effect that fixes silicon in sub-micron particles dispersed in the ς and η phases. Tensile experiments and fatigue tests demonstrate that the mechanical performances of the martensitic steel are preserved after coating. Comparison with similar experiments performed on a TRIP800 steel indicates that using galvanized martensitic steel is best worth in static applications.

HR-TEM observation of laser pressure weld of galvannealed steel and pure aluminium

Laser pressure welding was conducted by changing the laser power and the roller pressure in the previous experiment. It was revealed that dissimilar metal welding of galvannealed steel and pure aluminium was feasible in a wide range of welding conditions. When the roller pressure was more than 1.96 kN at the laser powers equal to or less than 1400 W, the joint strengths were so high that the specimens in the tensile shear and the peel tests fractured in the A1050 parent metal. In order to know the reason for such high strengths of joints with thick compound layers and the joining mechanism, the compound layer was observed by HR-transmission electron microscopy (TEM). The TEM observation results revealed that the main phase in the compound layer was the solid solution of Al + Zn. Moreover, the intermetallic compound was identified as FeAl, Fe2Al5, Fe4Al13 and Fe2Al5Zn0.4 phase by electron diffraction. The Fe3Zn10 (Γ phase) of Fe–Zn intermetallic compound was confirmed on a Fe base material. It is guessed that the joining areas were heated at a range of 782°C more than 665°C, a melting point of Al, by laser irradiation because the δlk phase aspect was not confirmed. Because the surfaces of A1050 and Zn plated layer were melted thinly, the layer was over 10 μm thicker. The reason for the production of high-strength joints with a relatively thick intermetallic compound layer was attributed to the formation of (Al + Zn) phase with finely dispersed intermetallic compounds.

Laser pressure welding of aluminium and galvannealed steel

Dissimilar metal joints of galvannealed steel and commercially available pure aluminium (A1050) sheets were produced by changing the laser power and the roller pressure by the laser pressure welding method. In this method, the YAG laser beam was irradiated into a flare groove made by these dissimilar metal sheets. In addition, the laser beam was scanned at various frequencies and patterns through the fθ lens using two-dimensional scanning mirrors. Then the sheets were pressed by the pressure rolls to be joined. The compound layers in the weld interface were observed by optical microscope, and the layer thicknesses were measured. The thicknesses were in the range of 7–20 μm. The mechanical properties of welded joints were evaluated by the tensile shear test and the peel test. In the tensile shear test, the strengths of the joints produced under the most welding conditions were so high that the fracture occurred through the base aluminium sheet. In the peel test of the specimens subjected to the laser beam of 1200–1400 W power under the roller pressure of 2.94 kN, the specimen fracture took place in the base aluminium sheet. Even if the compound layer was thick, high joint strength was obtained. In order to know the reason for such high strength of joints with thick compound layers and the joining mechanism, the compound layer was observed by the HR-TEM. The TEM observation results revealed that the main phase in the compound layer was the solid solution of Al + Zn. Moreover, the intermetallic compound was identified as FeAl, Fe2Al5, Fe4Al13, and Fe2Al5Zn0.4 phase by electron diffraction. The Fe3Zn10 (Γ phase) of Fe–Zn intermetallic compound was confirmed on a Fe base material. It is assumed that the joining areas were heated in a range of 782°C more than 665°C, a melting point of Al, by laser irradiation because the δlk phase aspect was not confirmed. Because the surfaces of A1050 and Zn plated layer were melted thinly, the layer was over 10 μm thicker. The reason for the production of high strength joints with the relatively thick intermetallic compound layer was attributed to the formation of (Al + Zn) phase with finely dispersed intermetallic compounds.

X-ray diffraction and scanning electron microscopy of galvannealed coatings on steel

The formation of Fe-Zn intermetallic compounds, as relevant in the commercial product galvannealed steel sheet, was investigated by scanning electron microscopy and different methods of X-ray diffraction. A scanning electron microscope with high resolution was applied to investigate the layers of the galvannealed coating and its topography. Grazing incidence X-ray diffraction (GID) was preferred over conventional Bragg-Brentano geometry for analysing thin crystalline layers because of its lower incidence angle alpha and its lower depth of information. Furthermore, in situ experiments at an environmental scanning electron microscope (ESEM) with an internal heating plate and at an X-ray diffractometer equipped with a high-temperature chamber were carried out. Thus, it was possible to investigate the phase evolution during heat treatment by X-ray diffraction and to display the growth of the zeta crystals in the ESEM.

レーザ圧接された合金化溶融亜鉛めっき鋼板と工業用純アルミニウム異材接合部の微細組織観察

The laser pressure welding was conducted by changing the laser power and the roller pressure in the previous experiment. It was revealed that dissimilar metals welding of GA steel and pure aluminum was feasible in a wide range of welding conditions. When the roller pressure was more than 1.96 kN at the laser powers equal to or less than 1400W, the joint strengths were so high that the specimens in the tensile shear and the peel tests fractured in the A1050 parent metal. In order to know the reason for such high strength of joints with thick compound layers and the joining mechanism, the compound layer was observed by the HR-TEM. The TEM observation results revealed that the main phase in the compound layer was the solid solution of Al+Zn. Moreover, the intermetallic compound was identified as FeAl, Fe2Al5, Fe4Al13 and Fe2Al5Zn0.4 phase by electron diffraction. The Fe3Zn10 (Γ phase) of Fe-Zn intermetallic compound was confirmed on a Fe base material. It is guessed that the joining areas were heated in a range of 782°C more than 665°C, a melting point of the Al, by laser irradiation because the δ1K phase aspect was not confirmed. Because the surfaces of A1050 and Zn plated layer were melted thinly, the layer was over 10μm thicker. The reason for the production of high strength joints with the relatively thick intermetallic compound layer was attributed to the formation of (Al + Zn) phase with finely dispersed intermetallic compounds.

450°C isothermal section of the Zn–Fe–Bi ternary phase diagram

The 450 °C isothermal section of the Zn–Fe–Bi ternary phase diagram has been determined experimentally using scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction (XRD). Five three-phase regions exist in the 450 °C isothermal section. Experimental results indicate that Bi is almost insoluble in the four Fe–Zn intermetallic compounds and in α-Fe phase, and the solid solubility of Fe in Bi-rich phase is also limited at 450 °C.

Influence of Ni-electrodeposited pretreatment on galvanized coatings of reactive steels

Four types of steel sheets containing 0.04%, 0.09%, 0.14% and 0.36% Si, respectively, were electrodeposited with a nickel layer of 3 μm in thickness and then galvanized in molten Zn at 450°C for various periods of time. The formation and growth of intermetallic compound layers on the surface of the samples were investigated by SEM and EDS. The experimental results show that the method of Ni-electrodeposited pretreatment can distinctively restrain the over-growth of the galvanized coatings of reactive steels and get eligible coatings with a proper thickness, bright appearance and strong adherence. EDS results indicate that a series of Ni-Zn intermetallic compounds γ′, γ and δ2 are first formed on the surface of the samples. With a prolonged immersion time, the Γ2-Fe-Zn-Ni and δ-Fe-Zn are formed accompanied by the gradual disappearance of γ′, γ and δ2 layer. After a longer immersion time, the lumpy ζ-Fe-Zn occurs between δ and liquid Zn and the Γ-Fe-Zn does between steel substrate and δ. Subsequently, ζ is in the form of a continuous and compact layer. The method of Ni-electrodeposited pretreatment changes the formation of Fe-Zn intermetallic compounds, which delay the growth of lumpy ζ and promote the growth of compact δ. Consequently, the abnormal growth of reactive steels is eliminated.

Friction and formability of galvannealed interstitial free sheet steel

Abstract Galvannealing is a process by which zinc-coated steel sheet is heat-treated. During heat treatment, the zinc and the iron diffuse into each other. The coating of a galvannealed steel sheet is composed of a mixture of Fe–Zn intermetallic compounds. The coefficient of friction and powdering of the coating are two important properties that need to be controlled in order to effectively use these coated sheet steels in stamping operations. The distribution of the intermetallic phases on the surface of the coating is a major factor affecting the friction and powdering behavior. A single interstitial-free steel with four different distributions of intermetallic phases in the coating as well as steels from commercial producers were examined. A flat-die tribometer and a bending-under-tension tribometer were used to investigate the frictional behavior of these sheet steels. The double-Olsen powdering test was used to investigate the powdering behavior of these sheet steels. As the amount of the zinc-rich (iron lean) ζ-phase (zeta phase) increased on the surface of the coating, the friction coefficient increased. The coefficient of friction also increased as the amount of iron content in the coating decreased. In contrast, with increased iron content in the coating the amount of powdering increased. In order to use a galvannealed sheet steel in a metalforming operation, there needs to be a compromised choice between frictional resistance and powdering behavior.

Correlation between the surface chemistry of annealed IF steels and the growth of a galvanneal coating

An attempt is made to establish possible relationships between the quantity of oxides and hydroxides of the alloying elements on the outer interstitial-free steel surface after the annealing process and the characteristics of the galvanneal coating formed. XPS measurements reflect a clear influence of the alloying element contents and the water vapour content or dew point (DP) of the atmosphere on the oxide and hydroxide coverage of the steel surface. In general, much less Fe–Zn intermetallic formation is seen on the Ti steel substrate than on the Ti–Nb steel. The reason for this may be related with the higher oxide/(Fe + Mn) atomic ratio on the external surface of the Ti steel substrate. With the Ti–Nb–P steel, an absence of Fe was observed in the coatings obtained on the surface of this steel annealed in atmospheres with a DP of −45 or −10 °C. A clear direct relationship has been found between the inhibition of growth of Fe–Zn intermetallic compounds and the fraction of the steel substrate surface covered by manganese oxides as a result of the annealing process. For the Ti–Nb–P steel the increase in the DP of the galvannealing atmosphere to 10 °C resulted in the incorporation of a significant Fe content in the coating. XPS analysis suggests a change in the surface film, and the formation of a phosphate enriched layer, instead of manganese oxide. A lower fraction of oxide coverage on the annealed steel substrate resulted in less of an impediment to the diffusion of iron atoms from the steel substrate to the zinc coating in the galvannealing process.

Thermal stress-induced fracture of coating layer of galvannealed steel

The thermal stress-induced multiple fracture of the Fe-Zn intermetallic compound coating layer of galvannealed steel was investigated for samples with IF (interstitial free steel) and SPCC (steel plate cold commercial, Japanese Industrial Standard) as substrates. The analysis of the measured length of the multiply fractured coating layer showed that the fracture strength of the coating layer was 260–280 MPa and the residual stress around 720–740 MPa of the coating layer was reduced to around 130–140 MPa through the multiple fracture. The influences of the coating layer thickness and the stress–strain curve of the substrate on the multiple fracture behavior of the coating layer were also clarified.

FIB and TEM Observations of Defects in Hot-Dip Zinc Coatings

The characteristic ability of FIB (focused ion beam) fabrication to remove materials from a very small and/or precisely located slab using an accelerated Ga ion beam were employed to prepare cross-sectional thin films of zinc-coated steel sheets composed of Fe-Zn intermetallic compounds. A few defects observed frequently on the galvannealed (GA) coating surface were analyzed. Streaky marks indicated the rich concentration of oxides at the interface between the galvannealed coating and the steel substrate. The annealing experiment indicated the existence of Mn and Si oxides on the steel substrate. The grain size of ferrite in the extreme surface of the substrate was smaller as compared with conventional IF (Interstitial Free) steels. Furthermore, some superlattice spots were observed at the fine ferrite grain. Defects that are termed 'wavy pattern' and 'dross' were also analyzed by the combination of the FIB and TEM (Transmission Electron Microscope) techniques.

<i>In-situ</i> Observation of Growth Behavior of Fe-Zn Intermetallic Compounds at Initial Stage of Galvannealing Process

In-situ observation was performed with X-ray diffraction technique using synchrotron radiation to reveal growth behavior of the Fe-Zn intermetallic compounds, theand � 1 phases, at the initial stage of galvannealing process. The galvanized sample and electroplated sample were used in the observation. The diffraction peak profiles were successfully obtained at intervals of 1 second with heating the sample, and the growth of the Fe-Zn intermetallic compounds was observed dynamically. In the galvanized sample including a small amount of aluminum in the coating, there was an incubation period of 7 seconds before the � 1 phase started to grow. The thickness estimated with the peak intensity of the � 1 phase increased in proportion to the square root of heating time when the incubation period was taken into account. In the electroplated sample including no aluminum in the coating, the thickness ofphase increased in proportion to the square root of heating time. The � 1 phase started to grow as soon as thephase occupied the entire coating. The thickness of the � 1 phase also increased in proportion to the square root of heating time. These results suggest that that the growth behavior of the � 1 phase at the initial stage of galvannealing is dominated by the interdiffusion between Fe and Zn, neither by interfacial reaction nor by autocatalytic reaction whether the coating contains aluminum or not. However, the growth behavior of the Fe-Zn during galvanizing or galvannealing process has been observed by static analyses such as a cross-sectional observation of the coating with an optical or electron microscope, and a measurement of iron contents in the coating using the samples quenched after annealing. In these analyses, it is very difficult to understand the growth behavior in detail because those reactions occur in a short period. Therefore, a rapid detection, i.e. ,' 'in-situ observation'' system is required to follow those reactions dynamically. The in-situ observation using X-ray diffraction method is a very useful technique to identify the Fe-Zn intermetallic compounds and to quantify their growth in the coating. In order to perform the in-situ observation of the growth behavior of the Fe-Zn in the coating, penetration length of X-ray and time definition of detector are important factors because it is necessary to observe the whole of coating having 10� 20 mm thickness, and to observe the rapid reaction. Although it is an easy way for achieving good time definition of detector to increase the intensity of source, it is very difficult for a conventional X- ray source to obtain enough intensity for the in-situ observation. Therefore, synchrotron radiation, which has higher energy and higher intensity than those of the conven- tional X-ray source, is necessary for the in-situ observation as an X-ray source. Recently, some synchrotron radiation experiments applied to an observation of the Fe-Zn reaction has been reported. 9-11) In this study, the in-situ observation of the growth of the Fe-Zn intermetallic compounds in the zinc coating during galvannealing process was performed with X-ray diffraction method using synchrotron radiation. In the experiment, a time dependency of diffraction profiles was detected quanti- tatively with galvanized samples including aluminum in the coating and electroplated samples including no aluminum in the coating. The growth behavior of the � 1 andphase in the coating at the initial stage of the galvannealing process was discussed with the quantitative results of their growth. Furthermore, the effect of aluminum in the coating on the growth behavior was also discussed.

Formation of the ζ phase at an interface between an Fe substrate and a molten 0.2 mass% Al–Zn during galvannealing

An interstitial free (IF) steel was dipped in a bath of molten Zn containing 0.2 mass% Al. The as-dipped (galvanized) steel was then annealed above the melting point of Zn (galvannealed), say at 773 K, for a period ranging from 1 to 30 s. Evolution of the microstructure of the Zn-containing coating was examined by transmission electron microscopy (TEM) and the chemical composition around the Zn(Al)/Fe interface was analyzed by energy dispersion spectroscopy (EDS) in a dedicated scanning transmission electron microscope (STEM). In the as-dipped (galvanized) steel a continuous layer of Fe 2Al 5 existed at the Zn(Al)/Fe interface, but no Fe–Zn intermetallic compounds were observed. Galvannealing at 773 K for 1 s resulted in the formation of the ζ phase at the Zn(Al)/Fe 2Al 5 interface, which grew at the expense of the Zn(Al) coating during the subsequent galvannealing. Possible mechanisms of nucleation of Fe–Zn intermetallic compounds are discussed.

In-situ high-voltage electron microscopy observations of reactions between molten Zn and Fe

Reactions between molten Zn and Fe have been observed directly by means of an in-situ heating experiment in a high-voltage electron microscope. In order to suppress evaporation of Zn during the in-situ heating experiment the specimen was coated with a plasma-polymerized hydrocarbon film. Mechanisms for the formation of Fe-Zn intermetallic compounds are discussed and it is concluded that all the models proposed so far are of doubtful validity.

The development of Fe–Zn intermetallic compounds in solid Fe/Zn and Fe/Zn–Al diffusion couples during short-term annealing at 400°C

The effect of aluminium alloying additions of up to 0.2wt.%Al to zinc in the early-stage formation of Fe–Zn intermetallic compounds was studied by means of diffusion couple experiments. Diffusion annealing was employed on Fe/Zn, Fe/Zn–0.1wt.%Al and Fe/Zn–0.2wt.%Al couples at 400°C for times ranging from 10 to 50 min. It was found that aluminium additions to the zinc alloy initially inhibited intermetallic compound formation. Furthermore, a localised phase was noted at the δ p / ζ interface in the ternary couples at short times (<30 min) which also inhibited phase growth. However, this phase was noted to have dissolved on further annealing (≥40 min), with the intermetallic phases that formed growing more rapidly than the binary couple at these times. It was also noted that intermetallic phase growth in the binary couple was dominated by the ζ phase at short times, but δ p growth dominated at times greater than 30 min. In contrast, the relative rate of growth of the ζ and δ p phases in the ternary couples remained almost constant with annealing time.

Factores que afectan a la estructura de los recubrimientos de cinc obtenidos por inmersión

Coating solidification during hot-dip galvanizing is a very complex process due to Al-Fe, Al-Fe-Zn and Fe-Zn intermetallic compounds development. Fe-Zn intermetallic are brittle and detrimental for the coating ductility, while the diffusion towards the surface of a segregated insoluble alloying such as antimonium causes the sheet darkness. Steel sheets of different roughness were hot-dip galvanized under different operation conditions using a laboratory scale simulator. The effect of steel roughness and process parameters upon coating characteristics were analyzed. Experimental results showed that the steel roughness affects the coating thickness, zinc grain size and texture as well as the out-bursts development, while the process parameters affects the Fe2Al5 morphology and antimonium segregation.

Characterization of the Fe-Al Interfacial Layer in a Commercial Hot-dip Galvanized Coating.

Recently there has been substantial interest in the formation of transient Fe-Al interfacial layers during hot-dip galvanizing and galvannealing. These layers delay the formation of Fe-Zn intermetallic compounds by preventing the interdiffusion of Zn and Fe. Despite the industrial importance of this inhibition phenomenon and the resulting research on the subject, there remains considerable uncertainty about the nature of the Fe-Al inhibition layer. In this study, the inhibition layer on commercially produced hot-dip galvanized steel is characterized using a combination of conventional and analytical SEM and TEM and X-ray diffraction. A reproducible technique for extracting the interfacial layer for the purpose of making plane-view TEM specimens is presented. Using this combined TEM, SEM, X-ray diffraction method, it is shown that the inhibition layer is composed of a layered structure of Fe2Al5 and FeAl3. It is also demonstrated that X-ray diffraction alone may fail to detect the FeAl3 phase and that a combined method using both TEM and X-ray diffraction is best suited for characterizing these interfacial layers. Additionally, it is shown that grain boundary diffusion of Zn within the Fe-Al interfacial layer may play an important role in the eventual transformation of the inhibition layer.