Experimental study on liquid metal free surface flow under magnetic and electric field for nuclear fusion

In the future application of nuclear fusion, the liquid metal flows are considered to be an attractive option of the first wall of the Tokamak which can effectively remove impurities and improve the confinement of plasma. Moreover, the flowing liquid metal can solve the problem of the corrosion of the solid first wall due to high thermal load and particle discharge. In the magnetic confinement fusion reactor, the liquid metal flow experiences strong magnetic and electric, fields from plasma. In the present paper, an experiment has been conducted to explore the influence of electric and magnetic fields on liquid metal flow. The direction of electric current is perpendicular to that of the magnetic field direction, and thus the Lorentz force is upward or downward. A laser profilometer (LP) based on the laser triangulation technique is used to measure the thickness of the liquid film of Galinstan. The phenomenon of the liquid column from the free surface is observed by the high-speed camera under various flow rates, intensities of magnetic field and electric field. Under a constant external magnetic field, the liquid column appears at the position of the incident current once the external current exceeds a critical value, which is inversely proportional to the magnetic field. The thickness of the flowing liquid film increases with the intensities of magnetic field, electric field, and Reynolds number. The thickness of the liquid film at the incident current position reaches a maximum value when the force is upward. The distribution of liquid metal in the channel presents a parabolic shape with high central and low marginal. Additionally, the splashing, i.e., the detachment of liquid metal is not observed in the present experiment, which suggests a higher critical current for splashing to occur.

A Special Extrusion-shear Manufacturing Method for Magnesium Alloy Rods Based on Finite Element Numerical Simulation and Experimental Verification

To research the influences of process parameters on a special extrusion-shearmanufacture method for magnesium alloy rods, deform-3d software with finite elementsimulations has been used to analyze the material flows of deformed magnesium alloysAZ31B during the extrusion-shear (ES) process, as well as the grain sizes anddistribution of extrusion loads, stresses and strains, and blank temperatures. Temperaturefields, stress fields, strain fields and temperature fields varying with different blankpreheating temperatures, extrusion speed and extrusion ratios were simulated. Influences ofdifferent extrusion conditions and different die structures on microstructures of rods prepared by ES process has been researched. Extrusion forces decrease with the increasing extrusion temperatures, decreasing extrusion ratios, increasing die channel angles and decreasing friction coefficients. The flow velocities of metal in the ES die increase with development of ES process. Increasing the channel angles and reducing the friction factors would increase the outflow velocities of metal, but it has little effect on the uniformity of metal flow. The increase in friction and extrusion speed would increase the temperatures of the ES die. The ES process can prepare finer and more uniform microstructures than those prepared by direct extrusion under the same conditions.

Research on Improvement of Cold Extrusion Technology of Connecting Screw

In order to solve the flange and dent defects in the end face of the cold extrusion of the connecting screw, the Deform3D software is used to simulate the extrusion forming process of the connecting screw, and the velocity vector is used to study the metal flow law of the part in the cold extrusion process. According to the velocity field and deformation law obtained by the simulation, the end face depression defect in the forming process is predicted. An improved production process is proposed, and the simulation results show that the new process scheme effectively eliminates the “sag” defect on the end face of the part. Finally, the extruded parts with qualified dimensional accuracy are obtained through experiments, and the results are basically consistent with the simulation results.

Effects of Rotation Speed on Microstructure and Mechanical Properties in Ti/Cu Dissimilar Friction Stir Welding

The dissimilar welding of titanium and copper by fusion welding is very difficult because the melting points of the materials are very highly different and strong brittle intermetallic compounds (IMCs) can be easily produced in welded zone and heat-affected zone, etc. Friction stir welding was employed as a type of solid-state welding for Ti/Cu dissimilar welding to obtain a sound welded zone and reduce the total process cost. This study investigated how the metal flow of the welded zone changes according to the variation in the rotational speed of the tool, from 450 rpm to 600 rpm. When the rotational speed was too high, the plastic flow of the softened material increased and intermetallic compounds such as TiCu, Ti2Cu3, and Ti2Cu, were generated in the Cu region of the welded zone. The microstructural evolution of AS (Advancing Side) and RS (Retreating Side) were investigated and the soundness of the welded zone and its mechanical properties were evaluated through the microstructural evolution. A high hardness value of 200 Hv or more was exhibited in some points, due to the formation of intermetallic compounds in the RS (Cu) region. Ti/Cu dissimilar friction stir welding at a welding speed of 50 mm/min and an appropriate rotation speed of 500 rpm showed a good welded zone and mechanical properties.

The Effect of Groove Shape on Molten Metal Flow Behaviour in Gas Metal Arc Welding

One of the challenges for development, qualification and optimisation of arc welding processes lies in characterising the complex melt-pool behaviour which exhibits highly non-linear responses to variations of process parameters. The present work presents a computational model to describe the melt-pool behaviour in root-pass gas metal arc welding (GMAW). Three-dimensional numerical simulations have been performed using an enhanced physics-based computational model to unravel the effect of groove shape on complex unsteady heat and fluid flow in GMAW. The influence of surface deformations on the magnitude and distribution of the heat input and the forces applied to the molten material were taken into account. Utilising this model, the complex thermal and fluid flow fields in melt pools were visualised and described for different groove shapes. Additionally, experiments were performed to validate the numerical predictions and the robustness of the present computational model is demonstrated. The model can be used to explore the physical effects of governing fluid flow and melt-pool stability during gas metal arc root welding.

Regularities of metal flow and defects transformation during rolling in roughing stands of a universal rail and structural mill

Experimental studies carried out in the conditions of a laboratory rolling mill have determined the regularities of the processes of metal flow and roll-out defects of billets during deformation in roughing stands of a universal rail and structural mill. In relation to the box size and gauges types "lying trapeze" and "trapeze", we have determined a significant irregularity of drawing coefficients of the surface layers by roll length and width, as well as the irregularity of drawing in the cross-section of the roll during rolling. It is shown that during deformation the surface zones adjacent to the ends of the roll are subjected to the greatest drawing, and dependence of irregularity of the drawing coefficients over the cross-section of the roll on the shape of the deformation zone has a distinct power-law character. We have established a significant effect of the drawing coefficient, as well as the location and spatial orientation of the billet defects, while the geometric dimensions of the defects don't have such influence on their roll-out coefficients. According to the obtained data, the defects located on the rolling edges are rolled out most intensively both in depth and width, and the transverse defects are rolled out the least intensively. At the same time, the rollability of any defects increases with the growth of drawing coefficient. It is determined that near the side edges of the roll there is an increase in the width (disclosure) of transverse and inclined defects relative to the rolling axis, as well as the disclosure of defects occurs at the end sections of the roll in relation to longitudinal defects. For internal defects, it was found that, similar to surface defects, an increase in the drawing coefficient during rolling contributes to an increase in their roll-out, while the rollout coefficient of internal defects in absolute value is significantly lower than this indicator for surface defects. It was determined that the minimum roll-out coefficient of internal defects occurs when they are located in the core of the sample, while the roll-out coefficient of such defects increases linearly when moving towards the roll surface. The influence of the location, spatial orientation, and drawing coefficient on the rollability of surface and internal defects is generalized in the form of regression equations. It makes it possible to use them in practice to predict the quality of finished rolled metal when changing rolling modes.

Studies on friction behaviour of aluminium AA4032 alloy during forging using ring compression test

In metal forming, friction has a negative effect on the deformation load & energy requirements, homogeneity of metal flow, quality of formed surfaces, etc.; however, its effect can be reduced through the use of proper lubricants. Mostly, in industrial applications, selection of proper lubricant for specific material is challenging and quantification of magnitude of friction at diework piece interface is essential. Hence, for metallic alloys, a realistic friction factor is needed to be known and used at the diework piece interface for better control of deformation process. Thus, this research, generally, aims at experimental investigation of the friction behavior of aluminum AA4032 alloy and selection of suitable lubricant for its effective processing using ring compression test and finite element (FE) simulations. Meanwhile, the effect of metal surface conditions and different lubricants namely palm oil, grease, emulsion oil and dry conditions on the friction behaviour has been evaluated. A commercial FEM software, DEFORM 3D, is used to analyze the flow of metal, determine the geometry changes of the specimen and generate friction calibration curves. The results revealed that the nature of metal surface and lubricating conditions have significantly affected the metal flow pattern, deformation load requirement, induced effective stress and strain, and geometry of the metal. The friction factor at die-work piece is determined for different lubricating conditions. Among lubricants employed, palm oil is found to be suitable and effective for industrial processing of aluminium AA4032 alloy, specifically for forging. The FE simulation results are in a good agreement with the experimental one.

Numerical Model Simulation of the Double-Roll Rotary Forging of Large Diameter Thin-Walled Disk

Double-roll rotary forging is an emerging plastic forming technology based on rotary forging. Owing to the advantages of being labor-saving, a small eccentric load, low noise and vibration, good uniformity, high surface quality, and material saving, it is very promising for the fabrication of large diameter thin-walled disks. To date, little relevant research on the double-roll rotary forging technology of large diameter thin-walled metal disks has been reported, and the deformation characteristic and the influence of three key parameters on the double-roll rotary forging process remain uninvestigated. Herein, a reasonable 3D rigid-plastic numerical model of the double-roll rotary forging of a disk workpiece is established under the Deform software environment. Based on the valid 3D numerical model, the deformation mechanism, and the effective laws of three key parameters (feed rate v of the lower die, rotational speed n of the upper die, and the initial temperature T of the disk workpiece) on the metal flow and force and power parameters in the double-roll rotary forging process have been explored. The research results provide valuable guidelines for a better understanding of double-roll rotary forging for the fabrication of large diameter thin-walled disks.