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In this research, ultrasonic melt treatment (UST) was used to produce a new ultrafine grade of spheroidal graphite cast iron (SG iron) and austempered ductile iron (ADI) alloys. Ultrasonic treatment was numerically simulated and evaluated based on acoustic wave streaming. The simulation results revealed that the streaming of the acoustic waves propagated as a stream jet in the molten SG iron along the centerline of the ultrasonic source (sonotrode) with a maximum speed of 0.7 m/s and gradually decreased to zero at the bottom of the mold. The metallographic analysis of the newly developed SG iron alloy showed an extremely ultrafine graphite structure. The graphite nodules’ diameter ranging between 6 and 9 µm with total nodule count ranging between 900 to more than 2000 nodules per mm2, this nodule count has never been mentioned in the literature for castings of the same diameter, i.e., 40 mm. In addition, fully ferritic matrix was observed in all UST SG irons. Further austempering heat treatments were performed to produce different austempered ductile iron (ADI) grades with different ausferrite morphologies. The dilatometry studies for the developed ADI alloys showed that the time required for the completion of the ausferrite formation in UST alloys was four times shorter than that required for statically solidified SG irons. SEM micrographs for the ADI alloys showed an extremely fine and short ausferrite structure together with small austenite blocks in the matrix. A dual-phase intercritically austempered ductile iron (IADI) alloy was also produced by applying partial austenitization heat treatment in the intercritical temperature range, where austenite + ferrite + graphite phases coexist. In dual-phase IADI alloy, it was established that introducing free ferrite in the matrix would provide additional refinement for the ausferrite.

With increasing clamping pressure, the bond density increases, the effective thickness decreases, and the plastic deformation at the Cu side near the welding interface regions below the sonotrode t...

As an auxiliary energy field for non-traditional forming processes, ultrasonic vibration has been proven effective for improving the forming characteristics of micro-forming process (MFP) in recent years. The ultrasonic vibration was often applied on the forming tool but seldom on the workpiece in the MFP, which was usually restricted by the random shape or size of workpiece. A special porous sonotrode platform and press machine was proposed by our research group to realize different ultrasonic vibration modes of tool vibration or workpiece vibration flexibly. In this paper, a new ultrasonic micro-extrusion process of tool-workpiece compound vibration was developed and the ultrasonic micro-extrusion experiments of copper T2 and the microstructure of the extrusion parts were studied for clarifying the influencing mechanism of different ultrasonic vibration modes and micro-extrusion characteristics in different forming directions. The results indicate that the tool-workpiece composite vibration mode can achieve better micro-forming characteristics than single workpiece or tool vibration mode, such as severe grain deformation effects, pronounced fiber flow lines, better micro-extrusion formability and significant flow stress softening effects. The different ultrasonic energy transmitted and absorbed by the forming materials under different ultrasonic vibration mode is the key factor for the abovementioned results. The research results are helpful to reveal the ultrasonic assisted micro-forming mechanisms of different ultrasonic vibration modes.

The spatial and size distribution of cavitation bubbles in Al-18wt.%Cu during ultrasonic melt processing at a fixed acoustic intensity input was exhaustively studied by utilizing synchrotron x-ray photography. The result reveals that the larger bubbles concentrate within an intense cavitation zone close to the radiation face of sonotrode, which is out-surrounded by a weak cavitation zone with bubbles sparse-inhabitation. Most cavitation bubbles obey a truncated size-Gaussian distribution, and the average size decreases as distanced away from the radiation face. The intensive cavitation zone contributes to an effectively refined solidification structure.

The ultrasonic joining of phosphor bronze sheets is analyzed using a 3-D finite element model for the study and prediction of the thermal profiles at the weld interface. The heat fluxes are calculated and assigned as boundary conditions during the thermal simulation. The forecast of temperature is done under various welding conditions. The maximum temperature obtained by transient simulation at the weld interface is 366.74℃. The continuous reduction in the temperature is observed towards the extremes of the weld metal. The sonotrode and the anvil achieve a lower temperature in comparison to the weld interface. The effect of clamping force and bonding ratio on the interface temperature is observed as positive. The model is validated with an error of 1.576% between the observed and predicted temperature results and a correlation co-efficient 0.96 is established between the simulated temperature results and the weld strength. Sufficiently strong joints were obtained at the optimum welding conditions with 74% joint efficiency. It is evident that the interface temperature has a strong linear relationship with joint strength and is a major deciding factor for achieving strong joints.

In this work, we study how ultrasonic cavitation melt treatment (UST) affects the temperature distribution, sump profile, and resulting microstructure in the direct-chill (DC) casting of an AA6008 aluminum alloy. Two 152 mm diameter billets were cast; one was treated with UST (UST-DC casting) in the hot top while the other was not (conventional DC casting). To investigate the temperature distribution, temperature was measured at multiple points in both billets. The sump profile was visualized by pouring Zn into the sump during casting. The microstructure was analyzed by measuring the grain size of as-cast billets. A numerical model of DC casting and UST-DC casting has been validated with the temperature measurements across the billets, and the experimental results agrees well with the numerical model. It is found that the sump profile quantification with thermocouple measurements is more accurate and less prone to interpretation than with Zn tracing. Numerical simulation results show that UST application in the hot top with sonotrode position at 20 mm above the graphite ring level depresses the liquidus isotherm but does not affect the solidus isotherm, resulting in a thinner transition region compared with conventional DC casting. Grain structure analysis verifies that structure refinement with UST has been achieved at the given sonotrode position. The strongest grain refinement was at the center of the billet with the average grain size 50% smaller than that without UST. The results are discussed in terms of the known mechanisms of UST, i.e. dendrite fragmentation and deagglomeration of nucleating substrates.

Proposed grain refinement mechanisms during ultrasonic solidification have been explained in terms of refinement between cavitation enhanced nucleation and fragmentation of dendrites according to the casting conditions. Solidification studies also describe the activation of nucleation under pressure pulses after bubble implosion as an additional supporting mechanism for grain refinement. This study clarifies some overlooked concepts and proposes a plausible grain refinement mechanism explaining the role of cavitation in pure Zn and a Mg–6 wt pct Zn alloy. Equivalent grain size and grain density have been obtained in pure Zn and the Mg–6 wt pct Zn alloy (grain size distribution ranging from 40 to 200 µm) when UST was applied after the onset of solidification. These fine, non-dendritic grains originate from the cavitation zone beneath the sonotrode. Significant thermal undercooling surrounding the low superheat sonotrode in contact with the melt is responsible for the formation of a solidified layer (typically the thickness is equivalent to the average grain diameter) at the sonotrode–melt interface. High-frequency vibrations with or without cavitation at this interface assist the separation of these fine grains, which are then carried into the melt by acoustic streaming. A possible mechanism for the separation of fine grains produced from the cavitation zone is explained with the help of established concepts reported for the ultrasonic atomization process.

Ultrasonic water processing is recognized as an emerging technology that has shown promising results for hydrogen production. It is also known that numerous parameters affect the sonication process, such as the ultrasonic efficiency, acoustic pressure distribution, input power, and the consequent cavitation activity. However, the current efficiency of such a technique limits its scalability for industrial production. Therefore, in this study, different sonoreactor geometries are developed, and a comprehensive assessment is probed to validate their performance. The study considered the effects of the geometrical parameters, such as the sonoreactor geometry, wall boundary conditions, and the number of sonotrodes. The results show that a slight change in the sonoreactors' vessel geometry while maintaining all other parameters constant significantly affects the reactor's pressure field distribution. The vessel geometry with a concave bottom wall has recorded the highest magnitude of the negative pressure, leading to more efficient cavitation bubbles. In contrast, the vessel geometry with a conical shape recorded the worst performance. On the effect of the number of sonotrodes, an eigenfrequency analysis is performed to check the excitable acoustic modes and frequencies to trigger resonance condition; the resonance condition will enhance the sonohydrogen process accordingly. The present study performs a hydrogen quantification analysis where the effects of increasing input power and maneuvering the geometrical effects are investigated. The maximum hydrogen production is recorded at 300 W in the amount of 2.5 × 10−9 mol/J when increasing the input power to one sonotrode mounted in a typical sonoreactor cylindrical shape at an energy conversion efficiency of 23%. For the study on the multiple sonoreactor, the amount of hydrogen produced is 308 × 10−9 mol/kWh at 180 W with an energy conversion efficiency of 33%.

Surface mechanical attrition treatment (SMAT) or ultrasonic shot peening method improves mechanical properties of metallic materials by causing the plastic deformation on their surface layer of the workpiece. In this research, an ultrasonic generator, an ultrasonic booster, a sonotrode, one hundred steel balls with the mean diameter of 1 mm, an optical microscope, an automatic roughness meter, and other supporting accessories are employed to conduct the experiment. The effect of shot peening time of the ultrasonic shot peening method on the surface coverage and the roughness of the treated aluminum sample A7075 is systematically investigated. The study reveals that shot peening time has a significant effect on the coverage and the surface roughness of the treated samples. The surface of sample is rougher with the increasing of shot peening time and the surface is full coverage after shot peening in 35s. The results of this study indicate that the method of surface mechanical attrition (SMAT) or ultrasonic shot peening is an effective method to induce the plastic deformation on the material. It also shows that this is a promising method to investigate the effects of experimental parameters on the microstructure, properties, and fatigue life of the material.

The formation of fine, non-dendritic equiaxed grains throughout a casting without the addition of refiners (i.e. independent of alloy chemistry), is made possible by using ultrasonic, magnetic or pulsed magnetic and electric current pulse techniques. The dominant mechanisms proposed for the grain refinement produced during the application of an external field are cavitation phenomena assisted nucleation or fragmentation of dendrites (ultrasonic field), wall crystals arising from the cold surface of the mould (electric current pulse, magnetic and pulsed magnetic fields). In all these cases fluid flow provides an additional contribution (e.g. reduced temperature gradients, growth rate and remelting of dendrites) to maintaining an equiaxed grain structure. The origin of equiaxed grains under an external field also depends on the casting conditions (volume and shape of casting) and the type of alloy other than the mechanisms specific to a particular technique. The current work aims to provide a detailed understanding of the various factors and mechanisms that influence the grain refinement achieved during the solidification of pure metals (magnesium and zinc) subjected to UltraSonic Treatment (UST). The role of the temperature range of UST application, time duration and an unpreheated sonotrode are examined with respect to the origin, evolution of equiaxed grain structure, morphology and the columnar to equiaxed transition. The origin of grains was analysed from three fundamental aspects that contribute to refinement (i) heterogeneous nucleation (ii) fragmentation of existing dendrites and (iii) grains produced from the colder surfaces (arising from mould walls or vibrating surfaces as wall crystals). A comparison of UST refinement with mechanical, low-frequency vibration, electric current pulse and magnetic field solidification of pure metals has also been provided to highlight the importance of the cold surfaces (sonotrode and mould wall) in influencing grain refinement.

Ultrasonic metal welding (UMW) has been widely applied as a high throughput solid-state joining technology for multilayers of sheet metal. During a typical UMW process, multilayer work materials are mechanically compressed by a knurl-patterned horn (also known as a sonotrode) onto an anvil tool, and a simultaneous in-plane sliding is applied to the horn at an ultrasonic frequency (20 kHz or higher) to help form the weld at the material interfaces. There is a great challenge in modeling and simulating the dynamic behavior of the work material and the whole weld formation process is subject to ultrasonic mechanical loadings imposed by the knurl-patterned horn tool. In this work, finite element (FE) models are developed to simulate the multilayer UMW process using knurl-patterned tools by directly applying the ultrasonic vibration as a model input. For a short weld duration of 0.1∼0.5 s, a high-fidelity FE modeling approach is developed using ABAQUS/Explicit to simulate the dynamic material response under the 20 kHz horn vibration. For an extended long welding duration of approximately 1.0 s, a computationally efficient hybrid approach is developed using both ABAQUS/Explicit and DEFORM-3D in order to leverage the strengths of each software package. The developed models are validated using experimental data of dynamic welding force, temperature, and weld geometry from in-situ process measurements of UMW. The 3D FE models developed in this study are the most comprehensive solution to date to simulate the complex material response subject to UMW process conditions and provide engineering guidance for the design of UMW applications.

Laser beam welding is a commonly used technology for joining similar and dissimilar materials. In order to improve the mechanical properties of the weld, the introduction of ultrasonic vibration into the weld zone has been proposed [5]. The ultrasonic system consists of an electronic control, a power supply, a piezoelectric converter and a sonotrode, which introduces the vibration into the weld zone. Its proper design is of great importance for the process performance. Furthermore, the effects of ultrasound in a melt pool need to be understood to evaluate and optimize the process parameters. In addition, it is important to find out the limits of ultrasonic excitation with respect to a maximum vibration amplitude. Therefore, firstly different methods of ultrasonic excitation are investigated and compared with respect to their performance. A system which is based on using longitudinal vibrations turns out to be the best alternative. Secondly, the system design is described in detail to understand the boundary conditions of the excitation and finally, simulations about the influence of ultrasonic vibrations are done by using a simplified model. The system is used to perform experiments, which aim at detecting the maximum vibration amplitude doing bead on plate welds of EN AW-6082 aluminum alloy. The experiments reveal a significant change of the weld shape with increasing ultrasonic amplitude, which matches the simulative findings. If the amplitudes are small, there is a marginal effect on the weld shape. If the amplitudes are high, melt is ejected and the weld shape is disturbed. In the present case, amplitudes over 4 µm were found to disturb the weld shape.

In the past few years, aluminum alloys have been widely used in the field of automation, aeronautical, and heavy industries due to their light weight, high specific strength, high corrosion resistance, and excellent formability. However, the properties related to microstructure and dispersed medium are constant throughout the past research. The present research work is focused on the tensile tests of LM25 (reinforced with 10% SiC) metal matrix composites (MMCs) for its applications in aerospace industry through ultrasonic treatment (UST) of the liquid melt by varying the ultrasonic sonotrode (US) power and ultrasonic frequency. The high intensity UST is carried out on the LM25 MMCs reinforced with 10% SiC (proportion by weight) in a temperature range between 850 and 750 °C. The preheated mold at 250 °C temperature is used to cast the liquid melt after the UST. The castings are produced by varying time intervals and temperature ranges at distinct US power levels such as (a) 65% and (b) 75%. The casting process samples are prepared as per ASTM standard for tensile tests to reveal the effects of the UST. In the present investigation, the effects of UST on melt temperature, processing time, US power, and ultrasonic frequency (kHz) are studied in detail.

Ultrasonic Assisted Grinding (UAG) has been established as an effective process for overcoming the drawbacks while processing hard and brittle materials such as ceramics. The change in process kinematics brought about by the superimposed ultrasonic vibrations is responsible for the unique characteristics in UAG in comparison with conventional grinding (CG). The sonotrode design is critical in ensuring the desired grinding characteristics in UAG. Hence, a hybrid UAG system has been designed by designing a block sonotrode and analysing its vibration characteristics using harmonic analysis of the system. The designed system has been assembled to an ultrasonic generator-control system and integrated to a conventional surface grinder. In order to ensure the effectiveness of the system, an experimental study has been performed using alumina and zirconia ceramic workpieces. The beneficial effects of UAG in terms of grinding forces and surface roughness has been obtained for the selected materials and machining conditions when compared to conventional grinding.

Uniformity of composition and grain refinement are desirable traits in the direct chill (DC) casting of non-ferrous alloy ingots. Ultrasonic treatment is a proven method for achieving grain refinement, with uniformity of composition achieved by additional melt stirring. The immersed sonotrode technique has been employed for this purpose to treat alloys both within the launder prior to DC casting and directly in the sump. In both cases, mixing is weak, relying on buoyancy-driven flow or in the latter case on acoustic streaming. In this work, we consider an alternative electromagnetic technique used directly in the caster, inducing ultrasonic vibrations coupled to strong melt stirring. This ‘contactless sonotrode’ technique relies on a kilohertz-frequency induction coil lowered towards the melt, with the frequency tuned to reach acoustic resonance within the melt pool. The technique developed with a combination of numerical models and physical experiments has been successfully used in batch to refine the microstructure and to degas aluminum in a crucible. In this work, we extend the numerical model, coupling electromagnetics, fluid flow, gas cavitation, heat transfer, and solidification to examine the feasibility of use in the DC process. Simulations show that a consistent resonant mode is obtainable within a vigorously mixed melt pool, with high-pressure regions at the Blake threshold required for cavitation localized to the liquidus temperature. It is assumed that extreme conditions in the mushy zone due to cavitation would promote dendrite fragmentation and coupled with strong stirring, would lead to fine equiaxed grains.

This study aims at evaluating the effects of surface mechanical attrition treatment (SMAT) on mechanical properties and corrosion resistance of NiCrBSi coatings deposited by high-velocity oxygen-fuel (HVOF) spraying. The as-deposited coating has a typical HVOF-sprayed morphology with unmelted and deformed particles, associated with voids and porosities, whereas after SMAT, the affected zone morphology is more compact, without porosity or crack. The thickness of the affected zone varies from about 30 to 100 µm according to the SMAT parameters. The surface roughness is much lower for SMAT-treated coatings (from Ra = 6.8 µm to a Ra ≈ 2.3 µm). Whatever the SMAT parameters used in this work, the treated materials are harder compared to the as-deposited coating (from 6.6 to 7.6 GPa). They exhibit compressive residual stresses around − 360 MPa, while tensile stresses with an average value of 180 MPa were evaluated for the as-deposited coating. In addition, the treated coatings show better wear resistance as well as better corrosion resistance in a 3 wt.% NaCl solution. The better compromise in terms of SMAT parameters corresponds to amplitude of vibration of the SMAT sonotrode of 15 μm and SMAT duration of 810 s.

Compared with Conventional Grinding (CG), the Ultrasonic Vibration-Assisted Grinding (UVAG) is more competitive for the machining of difficult-to-cut materials. In this article, a novel ultrasonic vibration plate sonotrode that enables the special longitudinal full-wave and transverse half-wave vibration modes was proposed. The vibration characteristics of the proposed sonotrode was theoretically studied based on the apparent elasticity and Rayleigh methods, achieving a single longitudinal workpiece ultrasonic vibration with an amplitude of 7.6 μm. A superior vibration uniformity was achieved, as indicated by the coupling coefficient of 0.5. Based on the proposed method, the normal and tangential grinding forces decreased by 35 % and 39 % in comparison with the CG, and an improved machined surface was obtained in the UVAG of Ti-6Al-4V, with the following characteristics: vibration amplification of 7.6 μm; a cut depth of 0.1 mm; a workpiece feed rate of 100 mm/min; and a grinding speed of 30 m/s.

Analysis of the joint strength between multiple thin aluminum strands in multi-strand single core cables after ultrasonic welding was carried out by performing T-peel tests. Herewith, the effect of two process parameters, namely the sonotrode pressure and the amplitude of sonotrode vibrations on the joint strength was studied. It was found that a larger applied pressure resulted in a larger maximum T-peel force, while large magnitudes of pressure and amplitude at the same time decreased the fracture energy of the weld and resulted in a weak joint. Furthermore, 3D reconstruction of the images captured by computer tomography of the joint revealed that for a high pressure value and a low value of vibration amplitude, the structure of the weld under the sonotrode was much more compact compared to a high value of vibration amplitude and a low value of pressure. To this end, volume fraction of the gaps between the aluminum strands inside the microstructure of the weldment was quantified and compared between specimens with different process parameters. Finally, a correlation between the joint strength and the microstructure porosity (voids) of the weldment has been presented and discussed.

Ultrasonic additive manufacturing (UAM) is a solid-state 3D printing technology. Steels can be welded with UAM at reduced ultrasonic power, achieving half the shear strength of bulk material. A higher weld power is demonstrated by using a cobalt-based sonotrode coating, achieving shear strengths comparable to bulk 4130 material. In-situ temperature measurements and fracture surface analyses indicate that higher power input promotes metallurgical bonding through softening and increased plastic deformation. Carbides and ferrite are found at 1 μm scale at key weld interfaces; no martensite is found due to an increase in critical transformation temperatures associated with high heating rates.

Ultrasonic spot welding (USW) of multilayer metal sheets is a critical process of lithium battery manufacturing. However, inconsistent weld quality is still an issue in multilayer USW which makes the online quality monitoring very necessary to provide rapid and reliable feedbacks of each workpiece’s weld quality. In this work, the displacement of the sonotrode in the clamping direction was monitored by a high-frequency displacement sensor in order to establish the relationship with the weld quality. Features of displacement signals were analyzed combined with changes in the plastic deformation and welding qualities which were characterized by the laser scanning confocal microscopy, the optical microscopy and the electron backscattered diffraction (EBSD). Besides, effects of welding parameters on the displacement signal were studied. Finally, the relationship between the displacement signal, the plastic deformation and the weld quality was established which can be used for the online quality monitoring of the multilayer USW.

To realize metal foil consolidation, a push–pull high-power ultrasonic consolidation resonance system is designed. Firstly, the structure of a high-power piezoelectric transducer was designed and calculated, the push–pull ultrasonic consolidation resonance system was designed according to requirements of ultrasonic consolidation. Secondly, the finite element modal analysis of the ultrasonic consolidation resonance system was carried out, the natural frequency and vibration mode were obtained. The dynamic simulation of the ultrasonic consolidation resonance system was carried out based on the four-terminal network method and MATLAB/Simulink, the displacement of piezoelectric transducer and the resonance system was obtained, the output displacement of piezoelectric transducer and the consolidation sonotrode end surface is 6 μm and 20 μm respectively. Thirdly, the dynamic model of the consolidation resonance system was established, according to the transfer function, the root locus method and frequency response method were used to analyze the characteristics of the system. Finally, the sweep frequency and impedance measurement of piezoelectric transducer were carried out, and the sweep frequency and fixed frequency measurement of the ultrasonic consolidation resonance system were also carried out. Experimental results show that the resonant frequency of piezoelectric transducer is 19,875 Hz, and the minimum impedance value is 261.43 $$\Omega$$ when the frequency is near 20 kHz. When applying 120 V and 160 V voltage signal, the resonant frequency is 20,039 Hz and 20,055 Hz, the maximum displacement of the sonotrode which is excited by double piezoelectric transducers is about 16 μm. The ultrasonic consolidation machine is fabricated, which can meet requirements of metal foil consolidation, such as high-power and amplitude.

AZ31B Mg alloys were joined with a pure Zn interlayer via ultrasonic-assisted transient liquid phase bonding. The formation and evolution of intermetallic compounds (IMCs) and the mechanical properties of the bonded joints were investigated. Results showed that joints could form within an extra short time of 0.1 s via eutectic reaction, eutectoid reaction and diffusion bonding. Mg-Zn eutectoid structures, IMCs of MgZn and MgZn2 formed inside the bonded joint. The width of the MgZn2 phase decreased with prolonged ultrasonication time, high ultrasonication power, and sonotrode pressure. The entire joint was characterized by eutectoid structures without MgZn2 at a high sonotrode pressure of 0.4 MPa. MgZn2 had a higher hardness and modulus than MgZn, Mg-Zn eutectoid structure, and Mg substrate. Joints fractured through the MgZn2 phase and eutectoid structure had shear strength values of 30 and 40 MPa, respectively.

The handling of solid reagents, catalysts and by-products is a daunting challenge in continuous-flow micro- and milli-reactors. Suspensions tend to settle over time leading to irrevocable clogging of the reaction channels. Herein, we describe our efforts to develop an ultrasonic milli-reactor which can handle such challenging solid-containing transformations. The reactor consists of a Langevin-type transducer, a sonotrode and an irradiating cylinder, on which a coiled glass capillary (12.88 mL) was attached. The ultrasonic milli-reactor was combined with an LED illuminating box and its efficacy was showcased in the photocatalytic aerobic oxidation of benzyl alcohol enabled by TiO2 particles exposed to UV-A irradiation. Ultrasound irradiation generates cavitation bubbles and causes a vigorous oscillation of both the cavitation and the Taylor bubbles. This improves the liquid mixing, the gas–liquid mass transfer and ensures resuspension of the settled particles. Moreover, these effects enhance the photon absorption by the semiconductor catalyst, which has an overall positive effect on the photocatalytic transformation.