Thermochemical Analysis of Phases Formed at the Interface of a Mg alloy-Ni-plated Steel Joint during Laser Brazing

The thermodynamic stability of precipitated phases at the steel-Ni-Mg alloy interface during laser brazing of Ni-plated steel to AZ31B magnesium sheet using AZ92 magnesium alloy filler wire has been evaluated using FactSage thermochemical software. Assuming local chemical equilibrium at the interface, the chemical activity–temperature–composition relationships of intermetallic compounds that might form in the steel-Ni interlayer-AZ92 magnesium alloy system in the temperature range of 873 K to 1373 K (600 °C to 1100 °C) were estimated using the Equilib module of FactSage. The results provided better understanding of the phases that might form at the interface of the dissimilar metal joints during the laser brazing process. The addition of a Ni interlayer between the steel and the Mg brazing alloy was predicted to result in the formation of the AlNi, Mg₂Ni, and Al₃Ni₂ intermetallic compounds at the interface, depending on the local maximum temperature. This was confirmed experimentally by laser brazing of Ni electro-plated steel to AZ31B-H24 magnesium alloy using AZ92 magnesium alloy filler wire. As predicted, the formation of just AlNi and Mg₂Ni from a monotectic and eutectic reaction, respectively, was observed near the interface.     

Investigation on effect of pulse correction on structure property in dissimilar welds of galvanized steel and aluminum alloy obtained by gas metal arc welding cold metal transfer

Gas metal arc welding cold metal transfer (GMAW-CMT) method with AlSi₃Mn filler wire was performed on welding of the 5754 aluminum alloy with thickness of 3 mm to the galvanized steel with thickness of 2 mm aluminum alloy to investigate the effect of pulse correction on structure and mechanical properties of welded samples. In accordance with results, GMAW-CMT provides good tensile performance. It was attributed to the various throat weld size and wetting actions because of the influence of pulse correction on structure of welded joints. It was inferred that on employing +5 pulse correction resulted in better and consistent tensile strength of 209 MPa. Furthermore, the results showed that increasing the pulse correction led to increasing of flow in the filler wire and in fact raising of brazed seam width and throat weld size. In addition, the thickness of intermetallic compound layer which was formed along the interface during the GMAW-CMT was varied by changing of pulse correction. It has been found that by increasing the pulse correction from–5 to +5, the throat weld size increased and consequently led to a change in the tensile strength of the welded joints.     

Analysis of various versions of the deoxidation of rail steel at OAO NTMK

The deoxidation of steel melted using various types of deoxidizers during out-of-furnace treatment is studied. The total oxygen and nitrogen content and the oxygen contents in the main types of oxide nonmetallic inclusions are determined by fractional gas analysis of steel samples taken from heats performed by various schedules. The main types of nonmetallic inclusions and their size distributions are found with qualitative and quantitative metallography. The oxygen content in the rail steel is minimal (5 ppm) when calcium carbide CaC₂ is introduced into the metal in tapping of a converter. When the metal is deoxidized using a steel wire filled with calcium or a steel wire filled with silicocalcium, the oxygen content in rail steel is ≈8 and ≈11 ppm, respectively. A comparison of various processes of rail steel deoxidation under the OAO NTMK conditions shows that the limitation of the aluminum content (no more than 30 ppm) or the use of a wire with a calcium or calcium carbide filler is more effective than the use of a wire filled with silicocalcium.     

Investigation of Microstructure and Mechanical Properties of Steel‐Aluminium Joints Produced by Metal Arc Joining

Joints of zinc coated steel (DX54D+Z200) to aluminium alloys (AW6181‐T4 and AW5182‐H111) were produced by the Cold Metal Transfer (CMT) technique, a modified metal inert gas (MIG) joining process. The aluminium alloy sheets and the AISi3Mn1 filler material are welded, while brazing occurs between the AISi3Mn1 filler and the steel sheet. At the interface between the Al‐based filler and the steel sheet, aluminium‐rich intermetallic Fe_xAl_y‐phases are formed. The comparatively low heat input of the CMT process and the choice of filler composition limit the thickness of the intermetallic phase seam (IMP) to a few micrometers. The structure of the intermetallic phase and its morphology are strongly influenced by the alloying elements (Mn, Si) of the filler. Tensile tests and crash tests of the steel to aluminium alloy joints revealed good mechanical properties.     

Production of thick 10XCHДΦ steel sheet of optimized composition for the construction industry

On the basis of newly developed steel, thick sheet for the construction industry may be produced, by smelting and casting, hot rolling, and subsequent heat treatment. In the oxygen-converter shop at OAO Magnitogorskii Metallurgicheskii Kombinat (MMK), a 370-t melt of steel is produced as a trial run. The metal is cast to slabs (thickness 300 mm), which are rolled on a 5000 mill to sheet (thickness 22–50 mm). A production technology for thick vanadium-steel sheet on the 5000 mill is developed: rolling with subsequent heat treatment (quenching + tempering); or controlled rolling with subsequent accelerated cooling to ensure the required strength class 390 and impact strength (KCU_?60, KCV_?20, KCA₂₀). The structure of the cast 10XCHДΦ steel sheet is investigated. Control tests of sheets used in the manufacture of metal structures for the Kazan football stadium confirm the high quality of the sheet.     

Friction Stir Brazing: a Novel Process for Fabricating Al/Steel Layered Composite and for Dissimilar Joining of Al to Steel

A novel process of friction stir brazing (FSB) for fabricating Al/steel layered composite (by multipass) and for joining Al to steel (by single pass) was proposed to avoid the wear of pin by steel, in which a tool without pin was used. FSB of 1.8-mm-thick Al sheet to steel sheet was conducted using a cylindrical tool with 20-mm diameter but without pin and using 0.1-mm-thick zinc foil as filler metal. For the rotational speed of 1500 rpm, sound joints were reliably obtained at the medium range of traverse speed of 75 to 235 mm/min, which fractured within Al parent sheet during tensile shear test. Furthermore, for peel test on the sound joints, Al and steel parent sheets tended to crack and deform, respectively. Metallographic examination showed that most Zn was extruded and the resultant interfacial structure consisted of several Al-Fe intermetallic compounds (IMCs) with a little Zn, less than 3 at. pct. The thickness of IMCs can be controlled to be less than 10 μm by properly increasing traverse speed (e.g., 150 mm/min). The metallurgical process of FSB was investigated by observing the microstructure of the longitudinal section of a friction stir brazed joint obtained by the suddenly stopping technique.     

Study on the Formation and Characterization of the Intermetallics in Friction Stir Welding of Aluminum Alloy to Coated Steel Sheet Lap Joint

Multimaterial fabrication such as joining of steel and aluminum is currently prominent in a variety of industries. Friction stir welding is a novel solid-state welding process that causes good joint strength between steel and aluminum. However, the phenomenon contributing significant strength at the interface is not yet clear. In the present study, the interface of the friction stir lap-welded aluminum and coated steel sheet having joint strength maximum (71.4 pct of steel base metal) and minimum, respectively, under two parameter combinations, i.e., 1000 rpm 50 mm min^?1 and 500 rpm 100 mm min^?1, was exclusively characterized by X-ray diffraction, transmission electron microscopy (TEM), concentration profile, and elemental mapping by electron-probe microanalysis. A TEM-assisted EDS study identifies the morphologies of large size Al₁₃Fe₄ and small size Fe₃Al-type intermetallic compounds at the interface. The diffusion-induced intermetallic growth (thickness) measured from a backscattered image and concentration profile agreed well with the numerically calculated one. The growth of these two phases at 1000 rpm 50 mm min^?1 is attributed to the slower cooling rate (~3.5 K/s) with higher diffusion time (44 seconds) along the interface in comparison to the same for 500 rpm 100 mm min^?1 with faster cooling rate (~10 K/s) and less diffusion time (13.6 seconds). The formation of thermodynamically stable and hard intermetallic phase Al₁₃Fe₄ at 1000 rpm and travel speed 50 mm min^?1 in amounts higher than 500 rpm and a travel speed of 100 mm min^?1 results in better joint strength, i.e., 71.4 pct, of the steel base metal.     

Production and Mechanical Properties of Roll Bonded Bulk Metallic Glass/Aluminum Laminates

Twin roll casting has been used to produce sheet of Mg₆₀Cu₂₉Gd₁₁ bulk metallic glass (BMG). Sheet can be produced with thicknesses between 1 and 4 mm, the width of sheet produced can be between 25 and 75 mm. The dimensional stability of the produced sheet in a cast run is ±1 mm in the width direction and ±0.05 mm in the thickness direction. As with all magnesium-based BMGs the sheet produced is strong yet brittle at room temperature. The maximum flexural stress of a twin roll cast Mg₆₀Cu₂₉Gd₁₁ BMG strip is 150 MPa with a flexural strain of 0.005. The Charpy impact energy of a Mg₆₀Cu₂₉Gd₁₁ BMG strip is 0.02 J. In order to improve the toughness values of the Mg₆₀Cu₂₉Gd₁₁, BMG strip laminates of BMG and aluminum alloy (UNS A91100) were produced via roll bonding. The introduction of aluminum layers to the sheet structure provides a barrier to shear band movement stopping the sudden catastrophic failure of the sheet. After rolling the BMG was examined via X-ray diffraction (XRD) to confirm that the BMG layer remained amorphous. The flexural stress, flexural strain, and Charpy impact energy properties of BMG-Al laminates are improved when compared to monolithic glass properties. The flexural stress values for laminates compared to the monolithic glass improve by 60 pct from 150 to 250 MPa. The flexural strain values improve by over an order of magnitude from 0.005 to 0.14. The Charpy impact energies increase by 2 orders of magnitude from 0.02 to 2.5 J.     

Surface aluminum alloy formation by electrodeposition from alkali chloride melts and by laser techniques

The work presented here deals with the surface aluminum alloys formation on AFNOR 35NCD16 steel substrate using two different methods: electrolytic surface alloy formation followed by a laser surface melting; laser surface alloying by aluminum powder injection in the remelted surface. The electrolytic-formed alloy presents the highest microhardness values (900 HV_80g) in comparison with that measured on the aluminum surface alloy obtained by laser techniques (520 HV_80g) and 550 HV_80g). Al₅Fe₂ phase was the only one identified in the electrolytic coating, before laser treatment. After laser melting of the electrolytic deposit, AlFe₃ phase is present. In the case of laser alloy formation by aluminum powder injection non-alloyed aluminum as well as the AlFe phase was identified.     

Study of the deoxidation of steel with aluminum wire injection in a gas-stirred ladle

In the present work, the deoxidation of liquid steel with aluminum wire injection in a gas-stirred ladle was studied by mathematical modeling using a computational fluid dynamics (CFD) approach. This was complemented by an industrial trial study conducted at Uddeholm Tooling AB (Hagfors, Sweden). The results of the industrial trials were found to be in accordance with the results of the model calculation. In order to study the aspect of nucleation of alumina, emphasis was given to the initial period of deoxidation, when aluminum wire was injected into the bath. The concentration distributions of aluminum and oxygen were calculated both by considering and not considering the chemical reaction. Both calculations revealed that the driving force for the nucleation fo Al₂O₃ was very high in the region near the upper surface of the bath and close to the wire injection. The estimated nucleation rate in the vicinity of the aluminum wire injection point was much higher than the recommended value for spontaneously homogeneous nucleation, 10³ nuclei/(cm³/s). The results of the model calculation also showed that the alumina nuclei generated at the vicinity of the wire injection point are transported to other regions by the flow.     

Wire rod of boron-bearing low-carbon steel for direct deep drawing

The Moldavian Metallurgical Plant has developed an integrated technology for making steel, a continous-cast semifinished product, and wire rod in accordance with the requirements of international standards. The technology involves optimizing the chemical composition of the steel (normalizing the contents of the chemical elements and the carbon equivalent C _e , inoculating the steel with calcium to lower its content of nonmetallic inclusions, and microalloying it with boron) and using efficient regimes for rolling and two-stage cooling (thermomechanical treatment) of the wire rod on a Stelmore line. The low-carbon wire rod is easily cleaned of scale by mechanical or chemical means and can be reduced from 5.5 to 0.5 mm in diameter by drawing at speeds up to 30 m/sec without an intermediate heat treatment to soften the wire rod/wire.     

Influence of Mode of Metal Transfer on Microstructure and Mechanical Properties of Gas Metal Arc-Welded Modified Ferritic Stainless Steel

This article describes in detail the effect of the modes of metal transfer on the microstructure and mechanical properties of gas metal arc-welded modified ferritic stainless steel (SSP 409M) sheets (as received) of 4 mm thickness. The welded joints were prepared under three modes of metal transfer, i.e., short-circuit (SC), spray (S), transfer, and mix (M) mode transfer using two different austenitic filler wires (308L and 316L) and shielding gas composition of Ar + 5 pct CO₂. The welded joints were evaluated by means of microstructural, hardness, notched tensile strength, Charpy impact toughness, and high cycle fatigue. The dependence of weld metal microstructure on modes of metal transfer and filler wires has been determined by dilution calculation, WRC-1992 diagram, Cr_eq/Ni_eq ratio, stacking fault energy (SFE), optical microscopy (OM), and transmission electron microscopy (TEM). It was observed that the microstructure as well as the tensile, Charpy impact, and high cycle fatigue of weld metal is significantly affected by the mode of metal transfer and filler wire used. However, the heat-affected zone (HAZ) is affected only by the modes of metal transfer. The results have been correlated with the microstructures of weld and HAZ developed under different modes of metal transfer.     

Analysis of Fluxless,Reactive Brazing of Al Alloys Using Differential Scanning Calorimetry

During this investigation, a technique was developed, using differential scanning calorimetry (DSC), to quantitatively analyze the influence of a Ni-based electrolytic braze promotor surface deposit on the furnace brazing of aluminum alloys. The purpose of this braze promoter was to induce a large exothermic surface reaction capable of disrupting a tenacious oxide present on the aluminum braze sheet faying surface. A cyclic DSC methodology was developed which was capable of a quantitative determination of the exothermic reaction (ΔH _exo) induced by the Ni plating. Samples with a small quantity of Ni plating exhibited significant “pre-reaction” between Ni and Al in the solid state which resulted in very low ΔH _exo values. Samples with higher quantities of Ni plating exhibited large ΔH _exo values up to 85 kJ/mole.     

New explosive welding technique to weld

Various aluminum alloys and stainless steel were explosively welded using a thin stainless steel intermediate plate inserted between the aluminum alloy driver and stainless steel base plates. At first, the velocity change of the driver plate with flying distance is calculated using finite- difference analysis. Since the kinetic energy lost by collision affects the amount of the fused layer generated at the interface between the aluminum alloy and stainless steel, the use of a thin stainless steel intermediate plate is effective for decreasing the energy dissipated by the collision. The interfacial zone at the welded interface is composed of a fine eutectic structure of aluminum and Fe₄Al₁₃, and the explosive welding process of this metal combination proceeds mainly by intensive deformation of the aluminum alloy. The weldable region for various aluminum alloys is decided by the change in collision velocity and kinetic energy lost by collision, and the weldable region is decreased with the increase in the strength of the aluminum alloy.     

Absorbed energy during compression and crushing of high strength steel sheets

The absorbed energy(E _a orE _a′) in static and dynamic compression of the test specimens constructed from high-strength steel sheets, and the influence of the mechanical properties of the sheet steels, on the first buckling load(P _max), were studied experimentally. The influence of sheet thickness and test specimen size onE _a, E_a′, andP was also investigated. The following relations were obtained: In static compression: P_max = 4.57(Σε =0.02)^0.62 · t^2.0 x 10³ (N) E _a = 79.4(Σε=0.02)^0.84· t^1.9 (J) and in dynamic compression:E _a′=K·(ΣB)^0.6 · t^1.9 (J) E_a′/E_a decreases with increasing tensile strength of steel sheet, and approaches about 1.2 at above 400 N/mm².     

Genetic Evolution of Inclusions in Interstitial-Free Steel During the Cold Rolling Processes

In present work, the genetic evolution behavior of inclusions in interstitial-Free steel sheets during the cold rolling processes have been investigated based on nano-indentation. The genetic evolution of inclusions in shape and position has been calculated by 2-D finite element model. The inclusions spread along the rolling direction and compress along the IF steel sheets thickness direction. The inclusion’s profiles calculated by simulation are consistent with that obtained by experiments. After multi-pass cold rolling, the inclusions can be moved a short distance toward the sheet surface. When the Al₂O₃ and TiN sizes are less than 30 and 20 μm, the displacements are approximately 6 and 10 μm respectively. While the diameter of Al₂O₃ is 100 μm, the maximum displacement is approximately 30 μm. Both the Al₂O₃ and TiN in the position of 1/2 of the sheet have little displacements after multi-pass rolling. On the contrary, the inclusion located at 1/8th position of the sheet, the actual displacements are more than 30 μm. The shorter the distance between the inclusion and the IF steel sheet surface, the larger the inclusion displaces. Furthermore, the relationship between inclusions and surface defects have also been discussed.     

The influence of boron uponr m value in aluminum killed drawing quality steel

The influence of boron levels up to 40 ppm on ther _m value and mechanical properties of an aluminum killed steel have been investigated. It is shown that boron levels in excess of 15 ppm cause a marked deterioration inr _m value from a level of 1.7 to that of 1.2. This change inr _m value is associated with a characteristic change in grain shape from elongated to equiaxed, an inhibition of aluminum nitride precipitation in the annealed sheet and a lowering of the intensity of {111{ poles. The influence of boron on aluminum nitride formation is discussed.     

Influence of Filler Wire Diameter on Mechanical and Corrosion Properties of AA5083-H111 Al–Mg Alloy Sheets Welded Using an AC Square Wave GTAW Process

In this work, the influence of filler wire diameter on AA5083-H111 weldments was studied. For that, square butt joints were made using an AC square wave gas tungsten arc welding process with the addition of filler wires of diameter 1.2 and 2.4 mm separately. The experimental results revealed that changing the filler wire diameter influenced the bead geometry and a complete penetration was achieved in both welds. The weldment processed with smaller diameter filler wire consisted of a wider heat affected zone with recrystallized grains and a fusion zone with coarser grain structure, thus reducing the mechanical properties and corrosion resistance. However, the use of larger diameter filler wire assisted in faster torch speed, resulting in lower heat input and thus finer equiaxed grains were produced in fusion zone. Also, finer grains along with the dispersion of finer Al₆(Fe,Mn) particles supported in obtaining the superior tensile and corrosion properties.     

Production of sheet with regulated surface microtopography

The production of sheet (including auto-industry sheet) with regulated surface microtopography is considered, beginning with the surface preparation of the working rollers and ending with the formation of roughness beyond the deformation region. The dependence of the impressionability (K _Ra in terms of the amplitude and K _Pc in terms of the frequency) on the individual and combined effect of various factors—such as the surface properties of the sheet, the reduction in the deformation region, the sheet thickness, the rough-ness of the blank, the presence of tempering or washing fluid, the roller diameter, and the tensile stress in the deformation region—is analyzed. The results are consistent with the model of supporting stress in the deformation region. This information is of practical interest to technologists producing sheet with regulated surface microtopography.     

Thermodynamic Calculation on Calcium Treatment for 26CrMo4S/2 Steel

Because CaSi core wire was not fed in external refining process for 26CrMo4S/2 steel making, it was found that the molar ratio of calcium versus alumina was very low and subsequently resulted in generation of much more non-metallic inclusions. Hence, it was reasonable to sugguest feeding appropriate amount of Ca core wire. Before the performance, the thermodynamic calculation had been carried out to obtain the theoretical amount of Ca wire to be fed. According to the practical data from steel plant and the thermodynamic data, it was calculated that only when 1.38 × 10^–4[%Al]_T^2/3 ≥ [%Ca]_T ≥ 4.97×10^–5[%Al]_T^2/3 in molten steel the Al₂O₃ inclusions could be properly modified.