The effect of excitation frequency on novel three-winding magnetic field-assisted MIG welding of 7075 aluminium alloy

Reducing arc heat input and obtaining equiaxed grains by hot-wire method during arc additive manufacturing titanium alloy

Wire and arc additive manufacturing (WAAM) is a competitive technique, which enables the fabrication of medium and large metallic components. However, due to the presence of coarse columnar grains in the additively manufactured parts, the resultant mechanical properties will be reduced, which limits the application of WAAM processes in the engineering fields. Grain refinement and improved mechanical properties can be achieved by introducing ultrasonic vibration. Herein, we applied ultrasonic vibration to the WAAM process and investigated the effects of wire feed speed, welding speed, and ultrasonic amplitude on the weld formation and grain size during ultrasonic vibration. Finally, a regression model between the average grain size and wire feed speed, welding speed, and ultrasonic amplitude was established. The results showed that due to the difference in heat input and cladding amount, wire feed speed, welding speed, and ultrasonic amplitude have a significant influence on the weld width and reinforcement. Excessive ultrasonic amplitude could cause the weld to crack during spreading. The average grain size increased with increasing wire feed speed and decreasing welding speed. With increasing ultrasonic amplitude, the average grain size exhibited a trend of decreasing first and then increasing. This would be helpful to manufacture parts of the required grain size in ultrasonic vibration-assisted WAAM fields.

The cast slab of low grades non-oriented electrical steels experiences twice diffusional solid phase transformation and demonstrates the features of strong morphological memory referring to columnar structure and texture memory referring to the preferred <100> texture at room temperature. In this paper, electron backscatter diffraction (EBSD), quasi-insitu observation of heating samples, and dilatometry are used to study and analyze the two kinds of memory phenomena. The results show that the cast slab consists of about 70% coarse columnar grains and 30% small equiaxed grains. Many small equiaxed grains show Σ3 misorientations with columnar grains indicating K-S orientation relationship obeyed during phase transformation. Coarse columnar grains show a typical <100>||growing axis orientation which is the same as solidified columnar grains. The quasi-insitu observation shows that transformation of columnar grained ferrite to austenite is very sluggish and columnar grained ferrite can still be seen even at a superheating degree of 176°C for 1 hour. Dilatometry measurement indicates that the starting transformation temperatures for a columnar-grain-dominant sample and a small-equiaxed-grain-dominant sample are similar, whereas their transformation extents are quite different with columnar grained sample showing a low dilatational amount due to insufficient transformation. It is most likely that the coarse columnar grains in cast slab are retained and untransformed high temperature δ-ferrite are not subjected to twice complete transformations. These retaining columnar grains in low grades of electrical steels can be used to improve magnetic properties through optimizing processing parameters.

Experiments were conducted to study the structural features of weld-solidified metal in commercial 5083 aluminum alloy and its influence on the fracture behaviors.The shape of weld bead was considerably influenced by welding variables and heat input. In these behaviors, height of reinforcement was influenced by the heat input but depth of penetration was done mainly by the welding current, while width of bead depended on the both of them.Structures of common 5083 alloy welds containing no refining elements consisted of fine columnar, coarse columnar, granular and feather grains. In these structures, the volume fractions of fine columnar and feather grains were increased with heat input but those of coarse columnar and granular grains were decreased reversely. The width of columnar grain had a tendency to increase with heat input. On the other hand, 5083 alloy welds containing small amounts of Ti-B showed the fine granular structure all over the fusion zone.When weld metals having fine columnar, coarse columnar and granular grains were stretched, crack occurred preferentially at the grain boundary of coarse columnar structure. In weld metals having taining feather grains, however, it was important to consider the relationship between the growth direction of feather grain and the stretching direction. Crack occurred preferentially at feather grain when stretched transversely to growth direction of feather grain but it did not occur in this way when stretched parallelly.

Effect of ultrasonic intensity on microstructure and mechanical properties of steel alloy in direct energy deposition-Arc

Biomaterial scaffolds have been increasingly used for tissue engineering applications as well as three dimensional (3D) cell culture models. Herein, we report a simple procedure combining compression molding, heating, and leaching methods for the fabrication of 3D micro-porous poly(ε-caprolactone) (PCL) biomaterial scaffolds. In this procedure, PCL micro particles are mixed with NaCl of defined sizes and compression molded, followed by heating and subsequent leaching of NaCl particles. This technique eliminates the gas foaming method, which is commonly used in the fabrication of PCL scaffolds. Process and scaffold parameters (i.e., heating time, NaCl concentration, and NaCl particle size) were varied and analyzed to determine their impact on the overall scaffold structural and mechanical properties. An increase in NaCl particle size led to an increase in pore area but did not significantly impact the mechanical properties of the scaffolds. Additionally, NaCl concentration did not show a significant effect on pore area, but considerably impacted the mechanical properties, water absorption capacity and porosity of the scaffolds. Variations in the heating time did not have an effect in the pore area, porosity, water absorption capacity or mechanical properties of the scaffolds. We also demonstrated the ability of these scaffolds to support the proliferation of breast cancer cells. Overall, these results elucidated structure-property relationships in the fabricated micro-porous PCL scaffolds. Further, this procedure could be potentially scaled up for the fabrication of micro-porous PCL scaffolds.

This paper proposes a novel bridging technique for the direction-controlled growth of nickel nanowires between pre-fabricated Au electrodes under magnetic field. The nanowires grew on the tip of an electrode with the assistance of an external magnetic field. The nanowires, about 150 nm in diameter and a few of micrometers in length, had high uniformity and grew spontaneously along the direction of the magnetic field. The growth direction of the nanowires was along the magnetic field gradient. Transport measurements show Coulomb blockade behavior. The nanowire interconnections yield potential barriers to carrier transport between the nanowires and the electrodes. Understanding and using the effects will allow the controlled fabrication of nanoelectronic devices in the near future.

In this study, stable composite multilayers incorporating magnetic montmorillonite (MMT) and weak polyelectrolyte were prepared under the assistance of a magnetic field. We reported a facile method for fabrication of covalently cross-linked Layer-by-Layer (LbL) multilayers using a photosensitive cross-linking agent 4,4′-diazostilbene-2,2′-disulfonic acid disodium salt that carried double azido groups. The multilayers after cross-linking presented improved stability against extreme solution conditions (basic solution pH = 14), and over 78.15% of magnetic MMT remained on the substrate, in clear contrast with the non-cross-linked multilayers, for which less than 8% of the magnetic MMT remained. The results of UV–Vis spectroscopy and scanning electron microscopy (SEM) measurements supported the improvement in the stability of the multilayers. Moreover, the assistance of the external magnetic field improved the LbL assembly efficiency and the cross-linking step achieved the molecular retarded release. When gauze was used as the substrate, the mass loading under the magnetic field was approximately 0.976 mg/cm2, which was 4.2 times the amount deposited on gauze without an external magnetic field. After interfacial modification of gauze using LbL multilayers, the static contact angle transformed from hydrophobic (111.25°) to perfect hydrophilic. When we employed aspirin as the target drug, it took 23 h for the cross-linked multilayers to achieve saturated release, as opposed to 9 h for the non-cross-linked multilayers.

Electron beam welding of the novel L12 nanoparticles-strengthened medium-entropy alloy Ni41.4Co23.3Cr23.3Al3Ti3V6: Microstructures, mechanical properties, and fracture

Insightful investigation for the strengthening mechanisms of Al–Cu alloy prepared by wire arc additive manufacturing

Directed energy deposition additive manufacturing of CoCrFeMnNi high-entropy alloy towards densification, grain structure control and improved tensile properties

Tailoring grain morphology in Ti-6Al-3Mo through heterogeneous nucleation in directed energy deposition

Abnormal growth of columnar grains and formation of Σ3 grain boundaries in non-oriented electrical steels

Improving the processability and grain structures of additively manufactured Al-Fe-Cu-xZr alloy: Experiment and high-fidelity simulation

The rate at which a electrochemical reaction takes place on an electrode is, in some cases, a function of the concentration of ions present in the interface which, then, depends on the transport of these ions from the solution. To control mass transport in the solution convection can be used, for example, stirring the liquid or rotating the electrode. A different form which leads to convection in the solution is the application of an external magnetic field. This is called magnetohydrodynamics, or simple MHD. Together with the electric field due to the interface they give rise to a Lorentz force, according to equation 1: FLorenz = q (E + v x B) . (1) This force is proportional to the velocity of the ions. Thus, the higher the velocity, the greater the relevance of the action of the magnetic field. Usually the effect of the magnetic field is compared to that of the rotating disk electrode, but the magnetic field have a vector character, and, then, the Lorentz force is proportional to the vector product of its direction and the velocity of the particles. Furthermore, the geometric shape of the electrode is also an important factor, since the magnetic density along the material depends on this geometry. Numeric simulations where performed using the finite elements methods to understand how the Lorentz force acted on the electrolyte under an externally applied magnetic field. The geometry used in the simulation was a disk of steel AISI 1020 with 3 mm of radius and 0.5 mm of height, and with an electric potential of 0.5 V. This disk represents a work electrode in an electrochemical experiment. The disk was centered in a homogenous magnetic field parallel to its surface, and immersed in air. The external magnetic field interacts with the ferromagnetic steel, and its generated a resultant magnetic field. Besides that, the electric potential of the disk generates an electric field around it. Considering that, in an electrochemical experiment, the ions move towards the electrode, it was used the perpendicular direction of the surface of the disk as the direction of the velocity of the ions. For the speed of the ions, the value of as magnitude of . It was calculated the Lorentz force using the magnetic and electric fields of the simulation, and the velocity described. The simulations were compared to physical experiments of corrosion of AISI 1020 steel samples in solutions of 1 M in open circuit experiments, at room temperature, during 600 seconds in a homogeneous applied magnetic field of 5000 Oe. The direction of the applied magnetic field was parallel to the surface of the work electrode. After each experiment, images of the surface of the electrodes were captured using an optical microscope. Figure 1 compare the Lorentz force calculated in the simulations with the images of the corrosion experiments. The simulations showed that the Lorentz force is asymmetric with respect to the surface of the electrode. In one side the magnetic field has the same direction of the electric field, while in the other side they have opposite directions. This asymmetry also appears in the image of the surface of the electrode after the electrochemical experiment. The corrosion has a crescent form, that only appears on one side of the surface, corresponding with the side of the simulation that has a greater intensity in the Lorentz force. Figure 1 – a) Simulation results for the Lorentz force and b) image of the surface of the work electrode after the open circuit experiment in an external magnetic field. Figure 1