Russian Journal of Non-Ferrous Metals最新文献

Abstract

TIG welding is the most common method for producing high-quality aluminium alloy welds. Variants of Tig welding will increase productivity. Some variants of TIG welding are hot wire TIG welding, activated TIG welding, and pulse TIG welding. Activated Tig welding has its own variants, such as FB-TIG, FZ-TIG, etc. for aluminium, TIG welding with argon inert gas is the most suitable welding technique. In activated TIG welding, various fluxes are used for welding SiO₂, TiO₂, and CaF₂, and the mixing of acetone and methanol will increase the penetration in the weldment. In this paper, we discuss the various fluxes used in aluminium welding for different variants of Tig welding and also the effect of welding parameters on aluminium alloys. also, Experiment was performed on aluminium AA7004 alloy with the convention, A-TIG and FB-TIG welding process. For the ensuring of quality of weld hardness, Microstructure, EDS, SEM and Potentiodynamic testing was performed.

Abstract

In this paper, an alloy with a group of Nb5Cr was prepared by hot pressing sintering and its phase composition was characterized. After hot pressing sintering, Cr element exists in the form of solid solution outside the Nb matrix, and a certain amount of NbCr₂ phase is formed. The bending strength of the obtained alloys is not less than 250 MPa, and the fracture toughness is close to that of H11 casting die steel. In addition to the mechanical properties of the alloy, the oxidation behavior of the alloy at different temperatures was also studied. The experimental results show that the change of the alloy is not obvious at 1000°C except for the dissolution of Cr element, and at 1000–1200°C, the alloy can spontaneously form a CrNbO₄ oxide film which is weakly bound to the alloy matrix. This is very conducive to the application of separation between the mold and the casting mold during casting. This product provides the casting industry with a material that can spontaneously form a Self-oxidizing film under high temperature oxidation environment and provides a usable choice for materials used in high temperature casting environment.

Abstract

The paper proposes a method for the formation of superhydrophobic electrochemical coatings based on copper with relatively high mechanical strength. The method of electrodeposition of copper composites with nanodispersed silicon carbide particles is considered as the main approach to obtaining such coatings. Electrochemical codeposition of nanoparticle agglomerates and a copper matrix makes it possible to obtain the required multimodal roughness of coatings. This coating, after treatment with stearic acid, acquires superhydrophobic properties. The paper presents data on the morphology, superhydrophobic properties and chemical composition of coatings. The optimal mode for the formation of such coatings has been determined. According to the results of mechanical tests, the superhydrophobic Cu–SiC composite is superior in resistance to dry friction to many other superhydrophobic coatings formed by electrochemical methods. The resulting coatings have a developed surface morphology, which makes it possible to achieve a wetting angle of 162°. This determines the increased corrosion resistance of copper coated with a superhydrophobic Cu–SiC composite in the salt spray chamber. The time until the first corrosion damages appears on copper in the salt spray chamber increases from several hours (without coating) to 3.5 days (with coating). In this case, the coating continues to remain generally superhydrophobic for more than a day, and after the loss of superhydrophobicity, it remains hydrophobic.

A thermodynamic assessment of the influence of alloying elements (Si, Mg, Cu, Ti) on the processes of phase formation during the production and liquid-phase processing of cast aluminum matrix composite materials with exogenous reinforcement (Al–SiC, Al–B₄C) has been carried out. It is shown that without suppression of the formation of Al–Si–C and Al₄C₃ carbides in the range of carbon concentrations from 0 to 4.5 wt %, the equilibrium phase composition of composites of the Al–SiC system in the solid state at temperatures from 423 to 575ºC lies in the three-phase region (Al) + Si + Al₄SiC₄, and below a temperature of 423ºC, the Al₄SiC₄ ternary carbide is replaced by the Al₈SiC₇ compound. In the Al–SiC–Mg system, the crystallization of composites containing more than 0.58 wt % magnesium ends in the four-phase region (Al) + Al₃Mg₂ + SiC + Mg₂Si. In the Al–SiC–Ti system, the end of crystallization is fixed in the three-phase region (Al) + Al₃Ti + SiC. In the Al–B₄C system, after suppression of the formation of the Al₄C₃ phase, with a deviation from the concentrations of elements that provide 10 vol % B₄C, aluminum borides are formed in the direction of increasing boron, and free carbon is formed in the direction of decreasing boron. Under equilibrium conditions, with a silicon content of up to 0.67 wt %, the crystallization of the Al–B₄C–Si system ends in the four-phase region (Al) + B₄C + AlB₁₂ + Al₈SiC₇, and at a higher silicon content, it ends in the region (Al) + Si + AlB₁₂ + Al₈SiC₇. In the Al–B₄C–Ti system, with a Ti content of less than 0.42 wt %, crystallization ends in the three-phase (Al) + TiB₂ + B₄C region.

This work presents comparative studies of structural and mechanical properties of a new β-Ti alloy Ti–10Mo–8Nb–6Zr exposed to conventional cold rotational forging and equal channel angular pressing (ECAP) at 250°C. The main phase in the initial quenched state after forging and ECAP is the BCC β phase. Broadening of X-ray lines of the β phase and TEM data indicate refinement of structure and increase in concentration of lattice defects after deformational treatment. In the initial state, the alloy has ultimate tensile strength of about 700 MPa, the yield stress of 450 MPa, and relative elongation to failure of ~30%. As a consequence of forging, the ultimate strength and yield stress of Ti–10Mo–8Nb–6Zr alloy increase to 1230 and 950 MPa, and after ECAP, they increase to 1280 and 1270 MPa, respectively; also, the relative elongation decreases to 6%. Significant improvement of strength properties of Ti–10Mo–8Nb–6Zr alloy exposed to ECAP makes it more promising for application in the medical field.

The effect of Na₂O on the viscosity, structure, and crystallization behavior of CaF₂–CaO–Al₂O₃–MgO–TiO₂ slag was studied using the rotating cylinder method, differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray diffraction analyses. The analyses demonstrated that with increasing Na₂O content, the viscosity and melting temperature of the slag decreased; however, the crystallization temperature increased. Na₂O acted as a network modifier to decrease the degree of polymerization in the titanoaluminate structure and consequently increased the mobility of ions in the slag structure. The network structures in the [AlO_nF_{4 – n}]-tetrahedral complexes and [AlO₄]-tetrahedra are depolymerized with the addition of Na₂O; however, the depolymerization had a minimal effect on the Ti–O stretching vibration. During the continuous cooling process of the slag without Na₂O, the crystalline phases of 11CaO·7Al₂O₃·CaF₂ were dominant, followed by CaF₂ and CaTiO₃. In addition to the first three phases, a new precipitated phase of NaAlO₂ was observed in the slag when Na₂O was added, and the sequence of crystallized precipitation during the continuous cooling process was 11CaO·7Al₂O₃·CaF₂, CaF₂, CaTiO₃, and NaAlO₂. The effective activation energy of 11CaO·7Al₂O₃·CaF₂ increased with increase in Na₂O content (0–3.9 wt %) and reached a maximum; however, a further increase in Na₂O content (6.6 wt %) decreased the effective activation energy of 11CaO·7Al₂O₃·CaF₂.

The influence of heating and cooling routes prior to aging of the Ti–22Nb–6Zr shape memory alloy (at %) on the intensity of formation of the isothermal ω_iso phase in the temperature range from 250 to 350°C for 1 and 3 h is studied by X-ray diffraction. It is shown that, for intense formation of the ω_iso phase, the most efficient scheme for entering the aging interval includes rapid water cooling water to room temperature from an annealing temperature of 600°C and subsequent rapid heating to an aging temperature of 300°C. All other routes used for entering in the aging interval, including slow cooling and/or heating, do not lead to the formation of an X-ray identifiable amount of the ω_iso phase, whereas, the β → ω_iso transformation in the temperature range from 250 to 350°C has a pronounced C-shaped kinetics with a maximum at 300°C. Aging in the entire range of 250–350°C leads to the dispersion hardening and an increase in the hardness of the alloy compared to the initial state. Moreover, the hardness gradually increases with an increase in the aging temperature from 250 to 300°C and remains constant in the temperature range of 300–350°C. The β-phase lattice parameter of Ti–22Nb–6Zr alloy remains unchanged over the entire aging temperature range of 250–350°C, which indicates the absence of noticeable diffusional redistribution of elements in the solid solution during the formation of the ω_iso phase. The w_iso phase formed during the aging of the Ti–22Nb–6Zr alloy over the entire temperature range of 250–350°C has the ratio c_ω/a_ω = 0.613 ± 0.002, which is similar to the ratio c_ω/a_ω for the shear-type athermal ω_ath phase, which in turn further emphasizes the identity of these two phase varieties.

In this study, a Mg22Al/10MgO composite could be produced at nearly full density by the field-assisted sintering technique at relatively low temperatures and for short time such as 400°C and 15 min under the vacuum-argon atmosphere. The Mg22Al matrix consists of 22 wt % Al, produced by mechanical alloying for 18h and then mixed 2 h with 10 wt % MgO as a reinforcement material. The microstructure of the sample was analysed using an optical microscope, SEM, EDS and XRD. Mechanical properties such as micro hardness, density and compression strength are also obtained. With a compression strength of 314.4 MPa and a hardness value of 137 HV, the composite obtained nearly theoretical density-TD of 0.99. The crystal distortion was measured and calculated by using XRD results. Furthermore, minor amounts of fine intermetallic compounds and oxides such as Al₃Mg₂, AlMg, γ-Al₁₂Mg₁₇ Al₂O₃ and MgO were detected. The field-assisted sintering technique, which allows rapid and low-temperature sintering, is used in this study to show that the mechanical properties of the mechanically alloyed microstructure are likely to be preserved during sintering. Furthermore, it demonstrates that when Al and Mg are mechanically alloyed, the alloying pair is a very suitable metal matrix material for composites in which a reinforcing phase, such as MgO, forms an insufficient interface.

Simulation model accuracy of quench induced residual stress in wrought magnesium alloy Mg‒Gd–Y–Zr–Ag–Er is tested by applying both isotropic and anisotropic criteria models in residual stress FEM simulation. Both hexagonal close-packed (HCP) lattice structure and asymmetry are considered in the manufacturing process. The distributions of residual stress in isotropic and anisotropic criteria models differ both in distribution and in value, which is due to stress-strain nonuniformity in extrusion direction (ED) and long transverse direction (LTD). Comparing the experimental and predicted errors of the two models, the anisotropic model improves the prediction accuracy by 8.3% in ED and 4.8% in LTD. Residual stress in LTD is always larger than that in ED by the XRD method, and the average deviation between the XRD method and the hole-drilling method is reduced through electropolishing.

Agglomeration of fine particles to produce agglomerates with desired properties (e.g., size distribution, internal pores, and stability) is a critically important precursor to heap leaching. In this work, the effect of the properties of agglomerates prepared by geopolymerization on column bioleaching was investigated. The agglomerates were prepared with different metakaolin addition and alkali activator composition. Reducing the metakaolin addition and increasing the sodium silicate content in the alkali activator was beneficial to increasing agglomerate size. With the increase of agglomerate size, size distribution uniformity also improved. NMR analysis showed that agglomerates prepared with minor metakaolin addition and alkali activator composed of fewer Na₂SiO₃ had more and larger pores. Column bioleaching experiments showed that the agglomerates with more and larger pores had lower permeability and higher copper extraction. For more efficient leaching, the added alkali activator did not need to contain NaOH. This study’s results can guide the agglomeration operation based on geopolymerization to prepare agglomerates that better meet the requirements of heap leaching.