Behavior Of Molten Metal Research Articles

Effect of Pouring Techniques and Funnel Structures on Crucible Metallurgy: Physical and Numerical Simulations

In the planar flow casting process of amorphous strips, the flow behavior of molten metal and the inclusion content in the crucible are crucial to the morphology and magnetic properties of the material. This study conducts a comparative analysis of the effects of non-immersed and immersed funnels, as well as various funnel structures, on the fluid flow and inclusion removal efficiency in the crucible by integrating numerical and physical models. The findings reveal that for the same pouring flow rate, the diameter of the liquid column in non-immersed pouring conditions is smaller than that of the funnel outlet, leading to a faster injection flow velocity. As a result, the melt in the crucible is subjected to severe impacts, accompanied by an increased possibility of slag entrapment. Conversely, immersed pouring substantially reduces the velocity of the molten metal at the funnel outlet, thereby extending the residence time in the crucible and diminishing the volume of the dead zone. Additionally, the molten metal backflows due to the negative pressure formed in the inner chamber of the funnel. The design of a trumpet-shaped funnel increases the effective volume while reducing the height of the backflow fluid, consequently reducing the velocity of the molten metal at the funnel outlet and prolonging the residence time. Compared to the conventional pouring process with the non-immersed funnel, the outlet velocity is reduced from 1.1 m/s to 0.12 m/s by adopting the immersed funnel with an inverted trapezoidal trumpet structure. This reduction results in a stable flow state, a 9.69% reduction in the dead zone volume fraction, and a 22.96% increase in average inclusion removal efficiency. These improvements demonstrate that a crucible funnel with a well-designed structure and the implementation of an immersion process can significantly improve the metallurgical effects in the planar flow casting process.

Effect of wire deposition rate on macro and microscopic characteristics of laser weld-brazed AA5083 aluminum alloy to galvanized steel joints and their corrosion response

ABSTRACT In this study, dissimilar metals, such as aluminium (AA5083) and galvanised interstitial free steel, were laser-brazed in a flange configuration using eutectic filler aluminium wire (4047, Al-12%Si). To investigate the effects of wire deposition rate on the characteristics of laser-brazed joints and to understand the factors contributing to corrosion in these joints. The wire deposition rates were varied while keeping other laser parameters constant. Changes in wire deposition rate were observed to affect the flow behaviour of molten metal leading to variations in the geometrical characteristics of the brazed joints and interfacial reactions as revealed by macroscopic examination. A series of corrosion tests, including electrochemical, immersion, and salt spray tests, were conducted on the laser-brazed joints. It was demonstrated by Immersion corrosion tests that the wire rate influenced the corrosion results for the laser-brazed joints. However, the salt spray test showed no substantial effect on corrosion with respect to different wire deposition rates. Furthermore, the electrochemical results indicated significant changes in the corrosion response of the brazed zone due to the presence of chemically dissimilar phases. A correlative discussion between laser parameters, observed microstructure, and their effects on the corrosion performance of the brazed samples is presented.

Research on the Impact Behavior of Molten Metal on the Mold Shell in Gravity Casting of Large Titanium alloy Castings

The impact behavior of molten metal on the mold shell in gravity casting of large titanium alloy castings by investment precision castings was studied. The physical and mechanical models of the impact of molten metal on the mold shell during the pouring process were constructed using numerical simulation. The effects of molten metal pouring rate and pouring weight on the maximum impact force of the mold shell were studied. The research results indicated that during the entire pouring process, the impact force of the first molten metal contacting the mold shell was higher than subsequent molten metal. The maximum impact force increased with the increase of pouring rate and pouring weight. The total impact force of the molten metal on the mold shell was composed of the instantaneous impact force converted from instantaneous impulse and itself gravity. The instantaneous impact force of the molten metal that first impacts the mold shell was much greater than its own gravity, while the impact force of the molten metal at the end of pouring was much less than its own gravity. The maximum impact force on the mold shell of a large casting with a pouring weight of 800kg was about three times higher than that of a medium-sized casting with a pouring weight of 80kg.The difference in the total impact force on the mold shell between them mainly comes from the instantaneous impact force converted from instantaneous impulse.

Mechanisms of Gravitational Influence on Weld Pool Behavior and Weld Bead Performance in Variable Polarity Plasma Arc Welding across Different Welding Position.

This article comprehensively explores the cross-scale effects of gravity on macroscopic flow formation and weld bead formation in variable polarity plasma arc welding. Gravity-induced changes in welding direction were achieved through welding at different spatial positions. The properties of the weld bead were investigated at various spatial locations. Additionally, an elemental tracing technique was employed to study the internal flow behavior of molten metal. In the flat welding position, there is an observable trend of increasing grain size in the welded bead, accompanied by a significant expansion of the coarse grain zone. Consequently, the properties of the weld bead in the flat position are inferior to those achieved in the vertical welding position. This phenomenon can be attributed to the accumulation of molten metal at the exit side of the keyhole, resulting in temperature accumulation. Research indicates that the internal flow within the weld pool plays a critical role in causing this phenomenon. The study's findings reveal the presence of two distinct vortex flow patterns within the weld pool: one aligned with the welding direction and the other directed towards the interior of the weld pool. Particularly noteworthy is the substantial expansion of the flow channel area in the flat welding position, which significantly amplifies the impact of internal flow. This enhanced flow intensity inevitably leads to the increased buildup of molten metal at the keyhole exit side. These studies lay the groundwork for achieving high-quality and controllable spatial-position welding.

Modeling and analysis of the plasma primary atomization for controllable preparation of high-quality spherical metal powders

Plasma primary atomization (PPA) is a unique and critical process in the plasma atomization (PA), which is a highly recognized materials processing technology for producing high-quality spherical powder, but there lacks of in-depth understanding and models on how the metal wire is converted into high-quality spherical metal powders. Therefore, experimental observations and theoretical analysis on the PPA process were carried out to reveal the behavior of molten metal for controllable preparation of the metal powders. Firstly, the typical stages in the PPA were firstly revealed by experimental observations. Secondly, heat and mass transfer models on PPA were established to reveal how the molten metal is generated and transferred on the wire surface. Thirdly, the behavior of the molten metal in PPA was phenomenologically modeled and quantitatively analyzed based on the experimental observations and the proposed models. As such behavior determines the average size and yield of the produced powders, two key influencing parameters were identified to quantitatively reflect the melting and transfer behavior of the molten metal respectively. Then, calculation equations for them were established based on the proposed models of PPA and then verified. With the proposed models of PPA and the established calculation equations of the key influencing parameters, the quality of the produced powders may be quantitatively controlled by optimal design of the plasma torch and selection of the processing parameters of PA.

Mechanism of the Influence of Weld Pool Wall Constraint on Weld Profile Formation in Gas Metal Arc Welding of Aluminum Alloy

This paper aims to clarify the influence of the wall constraint on the convection behavior of molten metal in a molten pool and improve the weld formation and mechanical property. In this paper, the flow behavior of molten metal under the action of weld pool wall constraint and driving forces is studied; especially, the mechanism of weld pool wall constraint on the flow behavior of molten metal and its influence on the weld formation are studied and verified. Additionally, the influence of convection behavior on the composition distribution and properties of weld are explored. The results show that the bottom wall of the molten pool has the function of constraint on the molten metal, which directly determines the profile and size of the upper and lower reinforcement of the weld. Therefore, the reinforcement forming coefficient Rc is proposed to value the diversion ability of the bottom wall. Meanwhile, the EDS results demonstrate that the flow pattern of molten metal has a significant effect on the distribution of the weld composition for different profiles of weld. For the weld with depressed upper reinforcement, its mechanical properties can be significantly improved because of its enhanced wall constraint when the supporting plate is added.

Formation, microstructure and mechanical properties of double-sided fiber laser welded ultra-high strength steel

The ultra-high strength steel with a thickness of 20 mm was welded by double-sided high-power fiber laser welding. The welding parameters were optimized according to the behavior of molten metal and formation of the weld. Necking, spatters and uneven formation occurred when the welding parameters were improper. Microstructure of the weld at most region was made up of martensite, while austenite could be found at the final solidified position where the solidification rate was relatively slow. The thermal effects of the second welding process resulted in the austenization of original martensite and then transformed to ferrite and carbide within the interlaminar weld. Hardness of the weld was much higher than that of base metal owing to the formation of martensite. Hardness decreased at the austenite zone and the interlaminar zone made up of massive ferrite. Solid solution of C element within the martensite improved the tensile strength but weakened the toughness of the weld, leading to the formation of cleavage planes at fracture surfaces of the top and the mid welds. Large angle between the grain growth direction and force loading direction was benefit to improve the tensile properties.

Numerical study of the effect of workpiece thickness on the interfacial behavior of a molten aluminum droplet on a zinc-coated steel sheet

In brazing, the interfacial conditions between the molten filler material and the solid workpiece are important, yet they cannot be observed experimentally. A two-dimensional axisymmetric simulation was conducted to analyze the behavior of a single droplet of molten aluminum on zinc-coated steel sheet as a simplified brazing process. The simulation models were verified through a comparison with experimental results in terms of bead shape, zinc distribution, and molten metal behavior. The results show that Young’s equation was not valid in explaining the wetting behavior because of the instant solidification. In this respect, the effects of the workpiece thickness and wetting angle on the bead width were negligible. Two periods of time, namely, the times for the temperature difference and solidification and their ratio (interface number), were defined to analyze the temperature behavior at the interface over time as well as the effects of workpiece thickness. The interfacial temperature behaviors tended to be divided into three regions: linear (or inversely proportional), singular, and convergence. The interface number converged to a value of one with the increase in the thickness.

Numerical analysis of molten metal behavior and undercut formation in high-speed GMAW

• A self-adaptive integrated arc heat-force distribution model is developed for GMAW. • Backward flow, gouging region and thin metal layer are processes initiating undercut. • Two dimensionless numbers are developed to predict the growth rate of undercut. A computational fluid dynamics model was established to investigate the undercut formation in high speed gas metal arc welding (GMAW). A double-ellipse integrated "arc current density-arc pressure-electromagnetic force-arc heat" distribution model, which could be self-adaptive to weld pool surface evolution, was developed. The multi-coupling transport phenomena in weld pool were simulated, and the effect of driving forces on the behaviors of molten metal and the formation of undercut was analyzed quantitatively. The results show that the high-velocity backward molten metal flow, large-size gouging region and prematurely solidified thin metal layer at weld toe were typical processes that initiated undercut. The evolution of undercut morphology was determined by the characteristics of inertia force, hydrostatic pressure and arc pressure in the different stages. Based on Buckingham- π theorem, the dimensionless growth rate of undercut area was a parabolic function of a dimensionless group including characteristics of stress state, molten metal flow and morphology of weld pool. This study clarified the physical origin of undercut defect in GMAW and might also provide some basic guidelines for its suppression.

Thermo-fluid simulation using particle method based on hand-pouring motion in casting process

Casting simulators are widely used to evaluate casting designs. However, most simulators using conventional methods such as FDM or FEM entail difficulty in evaluating casting designs sufficiently based on ladle motions or an operator’s pouring motion because they do not readily accommodate dynamically changing wall boundaries and do not easily accommodate the ladle motion as input. For this study, the authors extended the thermo-fluid simulation based on particle method, an earlier proposed method, so that the measured ladle motion can be input. The authors measured an operator’s ladle motion using marker tracking technique for AR and executed thermo-fluid simulations using the proposed simulation method. Comparisons of the experiments and the simulation results clarified that the proposed method can accurately predict flow behaviors of the molten metal resulting from the ladle motion. Comparisons of the proposed simulation and the simulation with a conventional simulation using the inflow condition of the constant flow rate clarified the importance of executing the simulation based on the ladle motion for high-accuracy prediction of molten metal behavior.

Computation-and-Experiment Study of Behavior of Molten Metal in Fuel Element and Fuel Assembly: Preliminary Experiments and Computational Models

This work investigates the motion of the liquid metal on the surface of a heated cylindrical rod. Experiment data are presented, and computational models modified in accordance with the experimental results are described. Exploration of the motion of molten metal over the surface of fuel column simulator both in gravitational runoff and at gas blowoff involved high-speed recording. Formation of rivulets and droplets has been recorded, as well as their separation from the surface at gas blowoff. Based on the experiments to simulate the melt motion, it is proposed to take into account the capillary interaction forces and to consider—in addition to solid, film draining—the rivulet runoff mode. Analysis of literature made it possible to suggest a criterion for the transition from the film mode to the rivulet mode, as well as a method of calculating the basic parameters for the rivulet mode.

Wetting behaviors of molten melt drops on polycrystalline Al2O3 substrates in high magnetic fields

We measured the contact angles of Al and Sn drops on polycrystalline Al2O3 substrates in various high magnetic fields at different temperatures. The contact angles of both Al and Sn drops on the Al2O3 substrates decreased under high magnetic fields. These decreases strongly depend on the temperature, magnetic flux density, magnetic properties of the metal drops, and the reactivity of the metal drops with Al2O3. Our results reveal that the wetting behavior of molten metal drops on ceramics can be modified by a high magnetic field.

Instrument to characterize the wetting behavior of molten metal on a solid substrate under high magnetic field.

A specially developed experimental platform to measure the wettability of molten metals on solid substrates under high magnetic fields in combination with the sessile drop method is presented in this work. The desired magnetic field was generated by a superconducting magnet containing a channel with a diameter of 300 mm, in which the main body of the experimental apparatus was installed. The developed setup was used to observe the in situ wetting behavior of a molten metal on a solid substrate and simultaneously record sample images in real time under a high magnetic field during the wetting process. Contact angles were determined by analyzing the recorded images with the help of analytical software. Experiments using a typical molten metal and a solid substrate were conducted. The results revealed that the wettability of the molten metal on the solid substrate was obviously improved under a high external magnetic field.

Optimization of magnetic oscillation system and microstructural characteristics in arc welding of Al/Mg alloys

AZ31B magnesium alloy and 6061 aluminum alloy were welded by the longitudinal magnetic field hybrid cold metal transfer (CMT) welding process. Three magnetic pole structures were designed and the distributions of magnetic field were simulated. The results show that the platform-shaped magnetic pole structure can improve the longitudinal direction of magnetic field in weld zone, which was suitable to redistribute welding heat source and decrease welding spatters. With the applied magnetic oscillation the welding width increased, the welding penetration and wetting angle decreased, meaning the wetting behavior of molten metal improved. The welding pores in the weld zone were suppressed with the increase of coil currents. The magnetic oscillation obviously reduced the thickness of Mg2Al3 layer and dispersed the distribution of strengthening phases Mg2Si that can prevent the crack propagation. The microhardness value at the interface layer was increased and the shear strength of the Al/Mg joints reached a maximum of 1411 N with magnetic oscillation, increasing by 30% compared to the normal welded joint. Fracture of the Al/Mg lap joints occurred at the Mg2Al3 layer/weld interface and Al side around the fusion line.

Effects of Different Parameters on Porosity Defects Between the Horizontal and Vertical Shot Sleeve Processes

The effects of different casting parameters on porosity defects between the horizontal and vertical shot sleeve processes are quantitatively studied based on experiments and simulations. The castings made using the two processes are characterized in terms of porosity defects by X-ray radiographic inspection and blistering formation by T4 heat treatment process. Experimental results indicate that much fewer porosities and blisters are formed in the castings made using the vertical process than those made using the horizontal one. Meanwhile, numerical simulations have been performed to quantitatively investigate the flow dynamics behavior of molten metal in the horizontal and vertical shot sleeves. The simulation results demonstrate that compared with the conventional horizontal process, the vertical shot sleeve process is more efficient in elimination of waves and reduction of air entrapment and oxide formation. Moreover, the vertical process needs a lower pouring temperature which can decrease hydrogen solubility in the molten metal; it has a smaller temperature gradient of molten melt which can reduce the formation of cold flakes and pre-solidified materials. Therefore, the vertical shot sleeve process is more competitive in improving the internal integrity of die castings.

Online monitoring of corrosion behavior in molten metal using laser-induced breakdown spectroscopy

The corrosion behavior of structure materials in direct contact with molten metals is widespread in metallurgical industry. The corrosion of casting equipment by molten metals is detrimental to the production process, and the corroded materials can also contaminate the metals being produced. Conventional methods for studying the corrosion behavior by molten metal are offline. This work explored the application of laser-induced breakdown spectroscopy (LIBS) for online monitoring of the corrosion behavior of molten metal. The compositional changes of molten aluminum in crucibles made of 304 stainless steel were obtained online at 1000°C. Several offline techniques were combined to determine the corrosion mechanism, which was highly consistent with previous studies. Results proved that LIBS was an efficient method to study the corrosion mechanism of solid materials in molten metal.

Influence of substrate surface morphology on wetting behavior of tracks during selective laser melting of aluminum-based alloys

AlSi12 samples were prepared by selective laser melting (SLM) under different processing conditions in order to obtain different top surface morphologies, where single tracks were produced using a fixed processing parameter to reveal the mechanism of the single track on different morphologies. The results show that the morphologies of single tracks changed with roughness of the top surface (Top Ra) of SLM parts, reflected in the variation of wetting angles on the surface processed previously as well as in dimensions of height, width, and depth at the cross-section of each single track. These changes were mainly caused by different wettability and flow behavior of the molten metal under various solidification environments of the single track during SLM. A poor solidification environment in which numerous balls existed limited an effective wetting behavior of molten metal on a previously processed surface of a SLM sample because of an increasing solid-liquid contact area, thus causing dramatical instability of the melt pool and attendant inferior processability of the single track. Meanwhile, under the action of surface tension, the molten metal had a high tendency to transfer into a pore near the single track to form an extending track or flow toward an upper region of melt to form a balling track, hence showing various morphologies of single tracks. This study proposes a theory of the solidification mechanism of single track on the non-ideal surface to provide a better understanding of the SLM processing of Al-Si alloy.

Numerical simulation of arc plasma and molten metal behavior in gas metal arc welding process

Numerical simulation of arc plasma and molten metal behavior in gas metal arc welding process

Validation of Meshless Method Based on Weighted Least Square Method for Simulating Electromagnetic Levitation

Electromagnetic levitation is a kind of magnetohydrodynamic phenomena, which is used for measuring the thermophysical properties of pure metals under high temperature. However, this phenomenon is complicated, and detailed mechanisms have not been clarified yet. This paper proposes the meshless method based on weighted least square method for the analysis of electromagnetic levitation. In this method, the fluid motion equation and the magnetic field equation are weakly coupled. The effectiveness of this method is verified through the analysis of the molten metal behavior.

Coupled 3-D Analysis Employing FEM and Particle Method—Experimental Verification of Cold Crucible Induction Melting

This paper proposes a coupled 3-D finite element method (FEM) and particle method for the analysis of cold crucible induction melting. In this method, the magnetic field is calculated by FEM and the fluid motion equation and the heat equation of a molten metal are calculated by the particle method. The effectiveness of this method is verified through the analysis of the molten metal behavior in the crucible.