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The corrosion behavior of austempered ductile iron (ADI) in molten aluminum (Al) is investigated in the present study. The results indicate that ADI demonstrates a superior corrosion resistance when exposed to molten Al for an extended period. The intermetallic compounds (IMCs) layer is primarily composed of Fe2Al5 and FeAl3. The thickness of intermetallic layer decreases from 49 to 30 μm with the increase of corrosion time, in which the thickness of Fe2Al5 decreases, while that of FeAl3 remains relatively unchanged. This outcome is primarily attributed to the formation of fine graphite nodules resulting from the decomposition of ausferrite. Additionally, the formation of Fe–Al–Si compound at the interface of IMC and ADI impedes the diffusion of Al atoms into ductile iron. [ABSTRACT FROM AUTHOR]

Online monitoring and real-time feedback on inclusions in molten metal are essential for metal quality control. However, existing methods for detecting aluminum melt inclusions face challenges, including interference, prolonged processing times, and latency. This paper presents the design and development of an online monitoring system for molten metal inclusions. Initially, the system facilitates real-time adjustment of signal acquisition parameters through a multiplexer. Subsequently, it employs a detection algorithm capable of swiftly extracting pulse peaks, with this task integrated into our proprietary host computer software to ensure timely detection and data visualization. Ultimately, we developed a monitoring device integrated with this online monitoring system, enabling the online monitoring of the aluminum alloy filtration process. Our findings indicate that the system can accurately measure the size and concentration of inclusions during the filtration process in real time, offering enhanced detection speed and stability compared to the industrial LiMCA CM (liquid metal cleanliness analyzer continuous monitoring) standard. Furthermore, our evaluation of the filtration process demonstrates that the effectiveness of filtration significantly improves with the increase in inclusion sizes, and the synergistic effect of combining CFF (ceramic foam filter) and MCF (metallics cartridge filter) filtration methods exceeds the performance of the CFF method alone. This system thus provides valuable technical support for optimizing filtration processes and controlling inclusion quality. [ABSTRACT FROM AUTHOR]

Comparative studies of the heat resistance of titanium, nickel, and carbon steel with coatings based on aluminides obtained by liquid-phase aluminizing with diffusion annealing at 850, 950°C were conducted. The influence of the holding time of aluminized samples of titanium, nickel, and carbon steel at 950°C on changes in their mass and oxidation rate was determined. [ABSTRACT FROM AUTHOR]

The heat resistances of titanium, nickel, and carbon steel with aluminum-based coatings produced by liquid-phase aluminizing with diffusion annealing at 850 and 950°C are studied and compared. The influence of the holding time of aluminized titanium, nickel, and carbon steel specimens at 950°C on the changes in their weight and oxidation rate is revealed. [ABSTRACT FROM AUTHOR]

In A356 aluminum alloy, the effect of electromagnetic stirring process on the melt quality such as density index, hydrogen and oxygen content, and the inclusion amount were investigated. To determine the optimal EMS condition for the aluminum alloy, a numerical study of EMS was applied and the electromagnetic force strength, which is the main source for stirring the melt, was predicted according to the EMS application conditions. In this study, the melt cleaning effect of the EMS process was analyzed by measuring the cleanliness of the solidified A356 alloy samples cast with and without the EMS process. After applying EMS process, the deviation of density index (DI) and hydrogen content in the cast samples according to the specimen position decreased, and it was confirmed that EMS was effective in homogenizing molten metal quality. In the case of the center of the top position, the hydrogen content in the sample decreased by 39.8% after EMS application, and a clear degassing effect was observed. Compared to the cast sample without EMS application, the amount of inclusions decreased by 40 to 55% when EMS was applied. From this, it can be concluded that EMS process has the effect of homogenizing and improving molten metal quality. [ABSTRACT FROM AUTHOR]

The heat resistance of titanium with coatings based on titanium aluminides deposited by liquid-phase aluminizing followed by a high-temperature hold is studied. The effect of the duration of the hold of titanium specimens in an aluminum melt and of the duration of the high-temperature exposure of the aluminized specimens on the chemical and phase composition, structure and heat resistance of the coatings is determined. [ABSTRACT FROM AUTHOR]

Aluminizing process of titanium in aluminum melts A7 and AK12 was investigated. The influence of aluminizing regime on the structure and chemical composition of the coating on the titanium alloy VT1-0 was established. [ABSTRACT FROM AUTHOR]

The oxide film on the scrap surface is one of the primary sources of oxide inclusions in the aluminum melt. Understanding the evolution of the oxide films in the aluminum melt is an important step for developing efficient recycling technologies and controlling the quality of the product. In the present study, we studied the evolution behavior of the oxide film in the aluminum melt. The oxide films were introduced via aluminum alloy scraps into the melt, and the micro-morphology and composition of the oxide film were analyzed by scanning electron microscope and energy spectrum. Results show that the oxide film on the surface of 1235 alloy foil, A356 alloy turning, and 5083 alloy scalping were broken into small flake oxide film and then transformed into minor granular oxide when the scraps were charged into commercial purity aluminum melt. However, in aluminum alloy melt containing magnesium, the oxide film remained an intact sheet shape up to a certain melt dwelling time. [ABSTRACT FROM AUTHOR]

Aiming at the problem that melt inclusions in the casting process of 7085 aluminum alloy seriously affect the ingot quality, this study introduces ultrasonic bending vibration into the melt of the launder in the semi-continuous casting process of 7085 aluminum alloy and investigates the online purification effect of ultrasonic bending vibration on the melt of 7085 aluminum alloy through a metallographic analysis, SEM analysis, and EDS energy spectrum analysis. The results show that, under the action of the ultrasonic, the inclusions in the aluminum melt are transformed from a large number of elongated large inclusions with a size of more than 50 μm, and granular inclusions with a size of about 5–15 μm, into a small amount of smaller than 30 μm point-like small inclusions. In addition, the average area ratio of inclusions in the melted sample was reduced from 3.835 (±0.05)% to 0.458 (±0.05)%, and the residual refining agent in the aluminum melt was effectively removed. It was also found that under the action of ultrasonic bending vibration, the tiny inclusions in the melt aggregate with each other, and interact with the residual refining agent in the melt to further grow, and are attached to the inner surface of the ceramic cavity channel to be removed. [ABSTRACT FROM AUTHOR]

The oxide film on the scrap surface is one of the primary sources of oxide inclusions in the aluminum melt. Understanding the evolution of the oxide films in the aluminum melt is an important step for developing efficient recycling technologies and controlling the quality of the product. In the present study, we studied the evolution behavior of the oxide film in the aluminum melt. The oxide films were introduced via aluminum alloy scraps into the melt, and the micro-morphology and composition of the oxide film were analyzed by scanning electron microscope and energy spectrum. Results show that the oxide film on the surface of 1235 alloy foil, A356 alloy turning, and 5083 alloy scalping were broken into small flake oxide film and then transformed into minor granular oxide when the scraps were charged into commercial purity aluminum melt. However, in aluminum alloy melt containing magnesium, the oxide film remained an intact sheet shape up to a certain melt dwelling time.

Fe is a detrimental impurity element in secondary, i.e., recycled, Al–Si cast alloys for castability and mechanical properties. Fe removal can be achieved by binding Fe into Fe‐containing, primary particles and removing these from the, thus, Fe‐depleted Al–Si alloy melt. Expanding the application of filters beyond the removal of nonmetallic inclusions to increase the Fe‐removal efficiency can contribute to production of high‐quality, secondary Al–Si alloys. The usability of Al2O3, 3Al2O3 · 2SiO2, MgAl2O4, Al2O3–C, and SiC filter materials in contact with Al7.1Si, Al7.1Si1.5Fe, and Al7.1Si0.75Fe0.75Mn alloys is evaluated in sessile‐drop and crucible experiments regarding wettability, chemical interaction, nucleation, particle formation, and the subsequent effect on the alloy composition. The Al–Si melts in contact with Al2O3 act as nonreactive, low‐wetting reference systems. MgAl2O4 and SiO2 in 3Al2O3 · 2SiO2 are reduced, forming low‐wetting Al2O3, whereas Mg and Si enrich in the droplet. In contact with SiC and Al2O3–C, a thin layer of high‐wetting Al4C3 is formed. In case of Al2O3–C, primary Fe‐containing particles are specifically attached to the Al4C3 layer, which is associated with oriented growth of that layer. The remaining Fe content in the melt is 0.9 at% and beneficial kinetic effects for the Fe removal are suggested. [ABSTRACT FROM AUTHOR]

It is well known that ultrasonic cavitation causes a steady flow termed acoustic streaming. In the present study, the velocity of acoustic streaming in water and molten aluminum is measured. The method is based on the measurement of oscillation frequency of Karman vortices around a cylinder immersed into liquid. For the case of acoustic streaming in molten metal, such measurements were performed for the first time. Four types of experiments were conducted in the present study: (1) Particle Image Velocimetry (PIV) measurement in a water bath to measure the acoustic streaming velocity visually, (2) frequency measurement of Karman vortices generated around a cylinder in water, and (3) in aluminum melt, and (4) cavitation intensity measurements in molten aluminum. Based on the measurement results (1) and (2), the Strouhal number for acoustic streaming was determined. Then, using the same Strouhal number and measuring oscillation frequency of Karman vortices in aluminum melt, the acoustic streaming velocity was measured. The velocity of acoustic streaming was found to be independent of amplitude of sonotrode tip oscillation both in water and aluminum melt. This can be explained by the effect of acoustic shielding and liquid density.

A mathematical model has been developed for single bubble motion and mass transfer for aluminum degassing under a compound field of ultrasonic and rotating flow, and it showed good agreement with experimental data. The effects of the ultrasonic frequency and acoustic pressure on the bubble size, bubble trajectory, and mass transfer rate between the bubble and melt were investigated. The ultrasonic frequency and acoustic pressure had little effect on the bubble trajectory, and its curve radius gradually increased with increasing distance. The retention time of the bubble in the compound field was much greater than that in a single rotating flow field, which is conducive for improving the purification efficiency. Under the experimental conditions of 450 rpm rotation speed and 1.1 m/s gas flow rate, the optimal parameters are a frequency of 50 kHz and an acoustic pressure of 100 kPa.

The article presents the results of research of the influence of technological modes of injection molding of aluminum alloys, such as the pressing speed, molding time in a mold, the method of depositing a separation coating on the mold surface and the composition of the lubricant on the erosion resistance of the separation coatings. It is established that the pressing speed is most significant from the factors that influence the thickness of the lubricating layer forming on the working surface of the mold. When using water-based coatings, the thickness of the separation coating layer on the mold surface is reduced from 19,0 to 3,2 mm; for fatty separation coatings with a powder filler from 40,0 to 7,0 mm. It was also found that the minimum thickness of the lubricating layer of the separation coating is observed in the gate area and is in the range from 1,2 to 1,7 mm for the investigated water-emulsion separation coatings and 6,0 to 11,0 mm for fatty greases. It is shown that when the separation coatings are applied by a mechanized method, the thickness of the lubricating layer is 2,0–2,2 times lower than when applying lubricant manually.

The mechanical properties of a layered foam aluminum–titanium composite material produced by the filling of Al melt into molds with pore-forming fluorine fluxes and titanium fixtures are investigated. The shear strength of the composite is determined by the adhesive bond between Al and Ti as well as by the strength of the intermetallic transition layer formed at the interface of the metals. To improve the adhesive bond, titanium is coated with aluminum, and the strength of the intermetallic transition layer is enhanced by alloying it with Co through an Al melt used for aluminizing of titanium. The effect of cobalt alloying on the wetting and spreading of Al melt in titanium during the formation of a composite material is studied. It is shown that alloying with 3% Co reduces the area of spreading of aluminum over titanium. When the titanium surface is activated with the K2TiF6 and K2ZrF6 flux, the wetting of titanium with the melt increases with an increase in the cobalt content, and when activated with KF-AlF3 eutectic, it decreases. Alloying with 2% Co increases the shear strength of the composite owing to the hardening of the intermetallic transition layer. When Ti surfaces are activated with K2ZrF6 flux, the shear strength of composites has the maximum value, which is due to alloying of the transition layer simultaneously with Co and Zr. [ABSTRACT FROM AUTHOR]

The mechanical and damping characteristics of titanium–aluminum foam composite materials obtained via casting of a mold with aluminum filled with pore-forming granules and titanium fittings are investigated in this work. Titanium reinforcement of aluminum foam is shown to increase the strength of a foamed material, slightly increasing its density. The damping properties of titanium–aluminum foam composites are close to those of a solid metal at an increase in the titanium content in the composite. [ABSTRACT FROM AUTHOR]

• Mechanical model of dynamic tensile fracture is proposed for solid and molten metals. • Pore nucleation is common, while size variation is specific for liquid and plastic solid. • Large scale MD simulations are used for verification and parameterization of the model. • Evolution of pore ensemble includes the stage of pore collapse. • The collapse of middle-sized voids is restricted by elastic stresses in the case of solid. Construction of the mechanical model for dynamic tensile (spall) fracture is one of the cornerstone problems in the mechanical description of the material behavior under dynamic loading. The spall fracture takes place for both solid and liquid substances, typically referred as cavitations in the latter case. We perform larger-scale MD simulation of the uniform triaxial stretching of molten and solid Al with the strain rate of 3/ns at different temperatures. Formation of multiple pores under used conditions of loading allows us to obtain detailed information about the evolution of pore ensemble at dynamic tensile fracture. This information can be used for verification of the mechanical models of dynamic tensile fracture. We formulate the mechanical models for the pore ensemble evolution in both liquid and elastic–plastic mater. The common part of the model describes the random nucleation of pores in the sample bulk. The size variation part of the model for liquid uses the Rayleigh–Plesset equation. The corresponding part of the model for elastic–plastic solid takes into account the dislocation activity in the pore vicinity. The detailed comparison of the model predictions with the MD data shows their adequacy in description of both the pore ensemble evolution and the general behavior of system parameters for room and elevated temperatures. The collapse of small pores after the relaxation of pressure from strong negative to close to zero values takes place for both molten and solid Al. In the case of melt, the larger and larger pores become collapsing with time, and the number of survived pores tends to one. In the case of solid, the elastic resistance of the surrounding material suppresses the collapse of the middle-sized pores, and only small pores disappear after the pressure relaxation. This feature does not allow one to use simple viscous growth models for pores in plastic solids. MD simulations show the nucleation of secondary voids in the vicinity of the primary nucleated pores and a more ordered defect structure around the pores in the case of low temperature of 100 K. These features cannot be addressed in the frames of the present mechanical model, which needs further development for description of the fracture at low temperatures. [ABSTRACT FROM AUTHOR]

The processes of wetting and spreading of zirconium-doped aluminum over titanium were studied under the conditions of the formation of layered aluminum-titanium composite materials with the activation of the surface of titanium with flux based on K2TiF6 salt. It is established that zirconium, owing to an increase in viscosity and a decrease in the fluidity of the melt, reduces the area of ​​spreading of aluminum over titanium. Doping the intermetallic layer between aluminum and titanium with zirconium leads to an increase in the adhesion strength of the composite layers. The maximum values ​​of adhesion strength are observed at a process temperature of 950°C and a zirconium concentration of 0.25%. [ABSTRACT FROM AUTHOR]

Results of experimental and numerical investigations of the process of creating coatings from a titanium-aluminum intermetallic compound by using an additive method are presented. It is demonstrated that the process of intermetallic compound formation is limited by the rate of titanium dissolution and diffusion in the aluminum melt. The proposed method can be applied for hardening titanium plate surfaces for their exploitation at high temperatures and pressures. [ABSTRACT FROM AUTHOR]

Compared to the traditional Star impeller, the designed impeller (hereinafter termed as the XSR impeller) has the characteristic of pumping which can promote degassing efficiency, and smaller area of the dead region and higher turbulent kinetic energy are obtained within the melt simultaneously. In the range of the discussed immersion depths of impeller (H = 185 mm, 315 mm and 435 mm), both too shallow depth (185 mm) and too deep depth (435 mm) are bad for the distribution of flow field. For the discussed rotational velocities of impeller (V = 390 rpm, 430 rpm, 480 rpm and 550 rpm), as the V increases, the intensity of fluid flow increases accordingly, and the area of lower turbulent kinetic energy reduces gradually. For the XSR impeller, the optimal immersion depth and rotational velocity are 315 mm and 550 rpm, respectively. The experimental data are in well accordance with the simulated results. Under the optimal process parameters, the average volume fraction of voids and inclusions of the A356 melt decreases by 98%. The as-cast A356 alloy with higher cleanliness exhibits an ultimate tensile strength (UTS) of 161 MPa, a yield strength (YS) of 72 MPa and an elongation (EL) of 14%. [ABSTRACT FROM AUTHOR]

Titanium dissolution in the aluminum melt and synthesis of an intermetallic compound at constant temperature and pressure are numerically simulated by the molecular dynamics method. Owing to titanium dissolution, the TiAl intermetallic compound is formed near the interface between the titanium crystal and aluminum melt. Based on the theory of weak solutions, a mathematical model of titanium dissolution in the aluminum melt is constructed. Dependences of the diffusion coefficient, equilibrium concentration of titanium, and dissolution rate on temperature are obtained. [ABSTRACT FROM AUTHOR]

A physical model of diffusion interaction of argon bubbles with an aluminum melt in the process of hydrogen outgassing from it by blowing an inert gas through the porous bottom of a refining vessel is presented. The dependence of the efficiency ε of the diffusion interaction of argon bubbles with the aluminum melt on the dimensionless complex criterion B has been investigated. Three characteristic regions of the dependence ε(B) have been distinguished. Analysis of this dependence made it possible to develop energy- and resource saving regimes of the technology related to the economics of argon. [ABSTRACT FROM AUTHOR]

Several methods of hydrogen production for feeding high-temperature fuel cells in high-efficiency environmentally friendly small-scale power plants are compared. As the most promising types of energy carriers for such installations, natural gas and aluminum are considered. The possibilities of producing a hydrogen- containing feed gas for high-temperature fuel cells on the basis of technologies we develop for the environmentally friendly burning of low-calorific fuels in volumetric matrix burner devices and for the efficient burning of aluminum in a high-temperature reactor are experimentally explored. It is shown that, in the technology of localized combustion of mixtures in a methane-conversion matrix, the specific yield of feed gas for fuel cells per unit area of the outlet section of the reactor is 3 times higher than that obtained for the combustion of aluminum−water mixtures at atmospheric pressure. The total specific power of the process is also 1.85 times higher. In the technology of distributed reaction, in the bubbling of steam through an aluminum melt, the specific yield of hydrogen per unit area of the reaction surface of the bubbles is an order of magnitude greater than the specific yield of hydrogen in the 'cold' reaction of aluminum with a 1 M alkaline solution. [ABSTRACT FROM AUTHOR]

[Display omitted] • An island-like oxide nucleation mechanism is found during the oxidation of aluminum melt. • The growth of the oxide obeys an island-by-layer model through the inwards O diffusion. • The oxidation kinetics switches from a linear law to a logarithmic law after the nucleation stage. Understanding on oxidation is critical for the improvement of aluminum melt quality which determines the properties of the aluminum alloy processed by casting. However, the oxidation mechanism of aluminum melt is still unclear in atomistic scale. In this work, we performed reactive molecular dynamics simulation to investigate the oxidation mechanism of aluminum melt on an atomic scale. Our results focus on the island-like nucleation on the melt surface and the following growth of the oxide film. The oxide grows via ion diffusion and the diffusion of O anions plays a greater effect. The evolution of the diffusion coefficient indicates an island-by-layer growth on the aluminum melt. Kinetically, the oxide growth obeys a linear law during the nucleation stage and switches to a logarithmic law after a closed oxide film forms. Besides, we emphasize the effect of oxygen content and ambient temperature on the formation of oxides. Our research can provide insights into the atomic-scale oxidation mechanism of aluminum melt which contributes to the better design for anti-oxidation methods during casting and the oxide-based functional materials. [ABSTRACT FROM AUTHOR]

A developed approach for a convenient fabrication of titanium nitride (TiN) particulate reinforced commercially pure aluminum (CP Al) composites via ultrasonic cavitation was proposed. The process involved the addition of large size TiN particles (average particle size of 264 μm) into Al melt at 1033 K. In the meantime, ultrasonic vibration was applied into the melt to comminute the large size TiN particles and disperse the produced fine TiN particles simultaneously. Microstructural characterization indicated that the produced TiN particles were much smaller than the starting TiN particles (average particle size of 15 versus 264 μm) and distributed uniformly in the matrix. The fine TiN particles were stable during the process and had a clean interface with the Al matrix. The ultimate tensile strength increased by up to 45% after the formation of fine TiN particles in the commercially pure Al matrix, whilst the hardness increased by a factor of 3. Dry sliding friction test showed that the coefficient of friction of the composites was more stable and lower than the CP Al matrix. [ABSTRACT FROM AUTHOR]

The results of analyzing the influence of operational parameters of the ejection nozzle on the characteristics of highly dispersed aluminum powder in production conditions at OOO SUAL-PM are presented. Measurements of dispersed characteristics of the spray when spraying the aluminum melt by the ejection nozzle are performed when varying the consumption and temperature of spraying gas in ranges of 0.17-0.21 m/s and 873-933 K, respectively, as well as the melt temperature in limits of 1153-1253 K. The results of determining the median diameter of the particles ( d ) and content of the highly dispersed fraction ( z) (with a particle diameter no larger than 10 μm) in the spray are presented. It is shown that, when modifying the operation parameter of the nozzle, the value of d decreases by 3.7-12.4%, while the magnitude of z increases by 0.4-3.2%. It is established that an increase in temperature of spraying gas affects the powder properties most effectively. [ABSTRACT FROM AUTHOR]

The quality requirements of the metals produced and the articles manufactured from them increases as non-ferrous metallurgy advances. In the course of aluminum production it is necessary to remove impurities present in the melt. The types of impurities present in aluminum melt and methods for removing them by filtering the melt are briefly reviewed. The existing ceramic filters and methods of manufacturing them are examined. [ABSTRACT FROM AUTHOR]

Factors causing the solid-phase dispersal of particles of alloying elements in the aluminum melt depending on their nature are considered. It is shown that the particles can be fragmented under the effect of uniform tensile stresses appearing due to the particles heating. The reasonability of using additional external effects (for example, magnetic-pulsed treatment of the foundry-alloy melt) to intensify the assimilation of silicon in liquid aluminum and provide the microcrystalline structure of the foundry alloy is substantiated theoretically and confirmed experimentally by the example of the Al-20 wt % Si foundry alloy. [ABSTRACT FROM AUTHOR]

Abstract: A continuous hydrogen-removal method for aluminum melt, spray degassing, is used to degass aluminum melt. The effects of various spray degassing parameters on hydrogen content and properties of aluminum are studied. The results show that, too high or too low melt temperature is unfavorable for hydrogen-removal. The high pressure of spraying gas is helpful for hydrogen-removal. The purge gas flow-rate has no effect on degassing efficiency of spray degassing. To gain a high degassing efficiency, bottom-blow purge gas should be combined with spraying process; otherwise, the degassing effect will be poor. [Copyright &y& Elsevier]

Abstract: EPMA and TEM analysis shows that there is a Ti transition layer around TiC particles in the α-Al grain center both in the usually solidified sample and in the rapidly solidified ribbon. Because the rapid solidification restrains the solute of the melt to diffuse before solidification, the rapidly solidified ribbon can conserve the instantaneous structure of the melt mostly, indicating that the Ti transition layer originates from the Ti transition zone in the melt. A new theory named as “Ti transition zone” theory has been proposed as a possible refinement mechanism for pure aluminum by Al–Ti–C refiner, and its formation model is given. The influence of the Ti transition zone on the melt viscosity was also discussed in this paper. [Copyright &y& Elsevier]

Effects of processing variables using such as the frequency of imposed field (f), imposed magnetic flux density (Be), processing time (t), the diameter of inclusions (dp) and the ratio of pipe radius to skin depth (r1/δ) on the electromagnetic separation (EMS) removal efficiency of inclusions from an aluminum melt were analyzed theoretically. It was found that the removal efficiency (η) reaches a maximum while r1/δ ranges from 1.5 to 2. In addition, wider effective range of r1/δ will be obtained with larger dp or higher f. Experimental results on aluminum melt show that higher frequency and magnetic flux density make for higher removal efficiency, matching well with the theoretical results. In the case of f=15.6 kHz, Be=0.1 T and t=10 s, more than 80% inclusion particles with 6-μm diameter can be removed. [Copyright &y& Elsevier]

[Display omitted] Low tensile strength of aluminum melt is a problem for traditional casting and additive manufacturing, while the tensile strength of solid aluminum is relevant for its application. Heterogeneities are considered as the main reason of decrease in the tensile strength, and investigation of their influence is a topical problem. We perform MD study of the effect of alumina inclusions, hydrogen bubbles and dissolved hydrogen on the tensile strength of aluminum in both solid and molten states. It is shown that uniformly dissolved hydrogen itself does not alter the tensile strength in most cases. An admixture of alumina can halve the tensile strength of solid aluminum, but in the case of a melt, the decrease in strength is only about 10% and even less at high temperatures. The most reducing the melt strength is the presence of non-collapsing bubbles stabilized by gas phase of hydrogen inside them. The tensile strength of the melt with hydrogen bubbles drops down in more than 10 times and even down to zero at high temperatures in comparison with the homogeneous melt for the total hydrogen concentration of about 1.4 at. %. Decrease in the hydrogen content leads to squeeze of the initial bubbles and increases the tensile strength. In the case of solid aluminum, the effect of hydrogen-filled bubbles does not depend on the hydrogen content and is equal to the effect of empty pores or alumina inclusions of the same size. Almost zero tensile strength of aluminum melt at casting and other technological processes can be explained by the combination of the admixture of hydrogen in the metal and spatial heterogeneities of the melt flow, which results in the hydrogen-stabilized bubbles tearing the melt at tension. [ABSTRACT FROM AUTHOR]

It is well known that solidification of molten metals occurs under the influence of transient unsteady phenomena, which are difficult to control in actual casting operation. Examples include buoyancy flows, natural heat convection, repeated remelting and solidification in mushy zone and solid shell at the mold interface. This paper presents the results suggesting that ultrasound waves, irradiated into the hot-top mold offers an attractive way to control the transient phenomena in DC casting of aluminum alloy billets. A novel mathematical model was developed to simulate the DC casting with considering transient melt flow, heat transfer, ultrasound propagation, acoustic streaming and solidification. It was found that ultrasound irradiation alters the solidification behavior of melt and sump evolution especially in the earlier stage of casting, however as the billet length increases, the sump profile becomes almost the same for both the ultrasonic and conventional castings. In this condition, the casting speed becomes the key parameter influencing the sump evolution and mushy zone volume. The results reveal that ultrasound-driven acoustic streaming and turbulent oscillations result in a suppression of buoyancy flow in the sump and lead to an increase of frequency of the melt temperature oscillations at the solidification interface. One of the useful results of these phenomena can be a more frequent repetition of remelting/solidification cycle and improvement of the billet quality, particularly the billet surface morphology. The effect of ultrasound irradiation on the billet morphology was verified experimentally using a pilot DC caster. [ABSTRACT FROM AUTHOR]

• The new coupled models were proposed to manifest the motion and mass transfer of the bubble under the compound field. • The ultrasonic frequency and acoustic pressure have little effect on the bubble trajectory, and the bubble spirals up. • The suitable ultrasonic parameters are the frequency of 50 kHz and acoustic pressure of 100 kPa. A mathematical model has been developed for single bubble motion and mass transfer for aluminum degassing under a compound field of ultrasonic and rotating flow, and it showed good agreement with experimental data. The effects of the ultrasonic frequency and acoustic pressure on the bubble size, bubble trajectory, and mass transfer rate between the bubble and melt were investigated. The ultrasonic frequency and acoustic pressure had little effect on the bubble trajectory, and its curve radius gradually increased with increasing distance. The retention time of the bubble in the compound field was much greater than that in a single rotating flow field, which is conducive for improving the purification efficiency. Under the experimental conditions of 450 rpm rotation speed and 1.1 m/s gas flow rate, the optimal parameters are a frequency of 50 kHz and an acoustic pressure of 100 kPa. [ABSTRACT FROM AUTHOR]

The wetting behavior was measured for Al2O3-C in contact with AlSi7Mg with a conventional sessile drop test (vacuum, 950 °C and 180 min) and a sessile drop test with a capillary purification unit (vacuum, 730 °C and 30 min). The conventional test yielded contact angles of around 92°, whereas the sessile drop measurement with capillary purification showed a strongly non-wetting behavior with a determined apparent contact angle of the rolling drop of 157°. Filtration tests, which were repeated twice, showed that the Al2O3-C filter possessed a better filtration behavior than the Al2O3 reference filter. For both filtration trials, the PoDFA (porous disc filtration analysis) index of the Al2O3-C filter sample was equal to half of the PoDFA index of the Al2O3 reference filter sample, indicating a significantly improved filtration performance when using Al2O3-C filter. Notable is the observation of a newly formed layer between the aluminum and the Al2O3-C coating. The layer possessed a thickness between 10 µm up to 50 µm and consisted of Al, C, and O, however, with different ratios than the original Al2O3-C coating. Thermodynamic calculations based on parameters of the wetting and filtration trials underline the possible formation of an Al4O4C-layer. [ABSTRACT FROM AUTHOR]