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Ultrasonic melt processing (UMP) has garnered significant attention from both academic and industrial communities as a promising solution to critical challenges in the metal casting industry. This technique offers a clean, environmentally friendly, and energy-efficient approach to improving melt quality and achieving structural refinement. However, due to the opaque nature of metals, understanding the fundamental mechanisms governing the interactions among ultrasonic bubbles, acoustic streaming, and the melt remains still challenging. This review traces the evolution of UMP research, from its inception in the mid-20th century to recent advancements, with particular emphasis on the application of state-of-the-art synchrotron X-ray imaging and computational modeling. These approaches have been instrumental in unraveling the complex, multiscale dynamics occurring across both temporal and spatial scales. Key findings in various metallic alloy systems are critically reviewed, focusing on new insights into cavitation bubbles, acoustic streaming, and the interactions of growing solid phases in different alloys. Additionally, the review discusses the resulting phenomena, including grain refinement, fragmentation, and the mitigation of solidification defects, in detail. The review concludes by identifying critical research gaps and emerging trends, underscoring the indispensable role of in situ studies and robust theoretical frameworks in advancing UMP. These developments are poised to reshape the future of innovation in materials science and engineering.

A novel magnesium (Mg)-based metal matrix nanocomposite (MMNC) was fabricated using ultrasonic melt treatment to promote the de-agglomeration of the bioactive glass–ceramic nanoparticles and the homogenization of the melt. The cast samples were then heat treated, machined, and hot rolled to reduce grain size and remove structural defects. Standard mechanical and electrochemical tests were conducted to determine the effect of fabrication and processing on the mechanical and corrosion properties of MMNCs. Compression tests, potentiodynamic polarization tests, electrochemical impedance spectroscopy, and static immersion testing were conducted to determine the characteristics of the MMNCs. The results showed that the combination of ultrasonic melt processing and thermomechanical processing caused the corrosion rate to increase from 8.7 mmpy after 10 days of immersion to 22.25 mmpy when compared with the ultrasonicated MMNCs but remained stable throughout the immersion time, showing no statistically significant change during the incubation periods. These samples also experienced increased yield stress (135.5 MPa) and decreased elongation at break (21.92%) due to the significant amount of grain refinement compared to the ultrasonicated MMNC (σY = 59.6 MPa, elongation = 40.44%). The MMNCs that underwent ultrasonic melt treatment also exhibited significant differences in the corrosion rate calculated from immersion tests.

In this work, a systematic review of the published literature was conducted, following the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses, on the ultrasonic treatment of magnesium-aluminium alloys for grain refinement. Scopus, Science Direct, and Web of Science databases were used in the literature search, which was finished by the 1st of June 2021. Seventeen articles met the eligibility criteria and were considered in this review, organized according to the type of ultrasonic treatment applied: isothermal (8/17) or continuous (9/17). Summary tables were used to categorize the information gathered from the articles, namely Treatment Conditions, Microstructural and Mechanical Analysis, and Mechanisms Behind Ultrasonic Grain Refining Ability. This systematic review aimed to structure and organize the available information regarding the ultrasonic processing of magnesium-aluminium alloys so new researchers can find a start point for their works and identify potential gaps in this research field.

The integration of ultrasonic energy into polymer melt processing enables control of melt-state dynamics and microstructure evolution in thermoplastic systems. By superimposing high-frequency mechanical vibrations onto conventional thermal and shear fields - or directly driving polymer plastification - ultrasound can induce transient viscosity reduction in many polymer systems, depending on material characteristics and processing conditions, improve filler dispersion, influence crystallization behavior and enhance flow stability under controlled conditions. This review presents a critical assessment of ultrasonic technologies in extrusion, injection molding and ultrasonic microinjection molding. Fundamental ultrasonic-polymer interactions - including oscillatory shear, viscoelastic dissipation and localized heating - are examined in relation to processing configuration and material response. Emphasis is placed on acoustic intensity, exposure time and energy localization in defining a processing window separating reversible rheological enhancement from irreversible molecular degradation. Across processing routes, ultrasonic activation can improve cavity filling, suppress melt fracture, refine morphology and facilitate nanocomposite processing and recycling. However, challenges related to spatial energy heterogeneity, scalability and industrial integration remain. Ultrasonic technologies should be regarded as energy-localized tools capable of expanding controllable processing windows when properly optimized.

Thermoplastic natural rubber (TPNR) was compounded with graphene nanoplatelets (GNP) via ultrasonication and melt blending. The effects of ultrasonication period (1-4 hours) and GNP weight fraction (0.5, 1.0, 1.5 and 2.0 wt.%) on the mechanical, thermal and conductivity properties were investigated. Results showed that the 3 hours of ultrasonic treatment on LNR/GNP gave the greatest improvement in tensile strength of 25.8% (TPNR/GNP nanocomposites) as compared to those without ultrasonication. The TPNR nanocomposites containing 1.5 wt.% GNP exhibited the highest strength (16 MPa for tensile, 14 MPa for flexural and 11 kJm-2 for impact) and modulus (556 MPa and 869 MPa for tensile and flexural, respectively). The incorporation of GNP had enhanced the thermal stability. It can be concluded that the GNP had imparted the thermally and electrically conductive nature to the TPNR blend.

The prediction of the acoustic pressure field and associated streaming is of paramount importance to ultrasonic melt processing. Hence, the last decade has witnessed the emergence of various numerical models for predicting acoustic pressures and velocity fields in liquid metals subject to ultrasonic excitation at large amplitudes. This paper summarizes recent research, arguably the state of the art, and suggests best practice guidelines in acoustic cavitation modelling as applied to aluminium melts. We also present the remaining challenges that are to be addressed to pave the way for a reliable and complete working numerical package that can assist in scaling up this promising technology.

Gelatin is a multifunctional protein with numerous applications in the food and pharmaceutical industries. The increased global demand for gelatin and issues regarding mammalian collagen have prompted an imperative urge for alternative sources. Therefore, this study aimed to explore the impact of ultrasound-assisted extraction on the physicochemical, functional, and bioactive attributes of gelatin obtained from Tenualosa ilisha scales. Ultrasound-assisted gelatin (UAG) extraction substantially increased the yield (34.49%), reducing fat and moisture content compared to water bath gelatin (WBG) extraction (20.06%). Sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) revealed α1, α2, and β chains, corroborating a triple helical conformation with UAG displaying shorter peptide composition. Fourier-transform infrared spectroscopy (FT-IR) showcased distinct peaks for amide- I, II, III, and A with decreased molecular order owing to ultrasound treatment. The WBG exhibited a lower UV-transmittance and a higher gel melting temperature, whereby, UAG displayed an excellent foaming capacity and stability with improved performance at higher concentrations. The WBG demonstrated superior emulsion activity and stability index, however, the emulsion activity of both gelatins declined with increasing concentrations. The gelatins showed a similar water-holding capacity, although WBG possessed a greater fat-binding capacity compared to UAG. However, UAG demonstrated enhanced antioxidant effects, revealing an IC 50 of 121.17 ± 2.38 for scavenging free radicals and an EC 50 of 184.48 ± 3.16 for reducing Fe 3+ , thus, minimizing oxidative stress. The findings will offer novel insights into the influence of ultrasound treatment on the properties of fish scale gelatin and developing methods for tailoring scale gelatin for food and pharmaceutical interventions.

Ultrasonic processing of solidifying metals in additive manufacturing can provide grain refinement and advantageous mechanical properties. However, the specific physical mechanisms of microstructural refinement relevant to laser-based additive manufacturing have not been directly observed because of sub-millimeter length scales and rapid solidification rates associated with melt pools. Here, high-speed synchrotron X-ray imaging is used to observe the effect of ultrasonic vibration directly on melt pool dynamics and solidification of Al6061 alloy. The high temporal and spatial resolution enabled direct observation of cavitation effects driven by a 20.2 kHz ultrasonic source. We utilized multiphysics simulations to validate the postulated connection between ultrasonic treatment and solidification. The X-ray results show a decrease in melt pool and keyhole depth fluctuations during melting and promotion of pore migration toward the melt pool surface with applied sonication. Additionally, the simulation results reveal increased localized melt pool flow velocity, cooling rates, and thermal gradients with applied sonication. This work shows how ultrasonic treatment can impact melt pools and its potential for improving part quality.Developing a fundamental understanding of how external fields are applied and influence additive manufacturing processes is crucial for in-situ microstructural control. Here, high-speed synchrotron X-ray imaging and computational fluid dynamic simulations reveal the effect of ultrasonic vibration on laser-generated melt pool dynamics and solidification of an aluminum alloy.

A comparison study between an electric current applied in the pulsed mode (ECP), ultrasonic treatment (UST), and melt stirring treatment (MST) was performed to understand the origin of equiaxed grains during the solidification of pure Al. ECP and UST were applied at 760°C and 700°C before the onset of nucleation, and at one temperature range after the onset of nucleation at 661°C. UST produces excellent refinement in all three temperature ranges compared to ECP. Interestingly, application of the MST process at 661°C over the surface of the solidifying melt also resulted in significant refinement comparable to that of UST (grain size of ~260–460 μ m).ECP, UST, and MST techniques differ in terms of the dominant mechanism influencing the grain refinement. Therefore, the present work analyses and discusses the grain refinement mechanisms based on nucleation, fragmentation, and a crystal separation mechanism for the origin of fine grains.

The properties of basalt fiber reinforced polypropylene composites (BF/PP) were improved by ultrasonic treatment of resin building pressure to assist melt impregnation. Combined with the study of ultrasonic pressure building theory, the mechanical properties of the modified composites were analyzed using the characterization of tensile, flexural and impact strengths in response to porosity and fracture rate. The effects of ultrasonic power, frequency and distance of action on resin building pressure and composite properties were investigated. The results showed that the best effect was achieved when the ultrasonic frequency was 25 kHz, the ultrasonic power was 300 W, and the action distance was 4 mm, at which time the porosity of the prepreg was reduced to 2.99%, the fracture rate was 3.36%, and the tensile, flexural, and impact strengths were 108.73 MPa, 116.81 MPa, and 51.59 KJ.m −2 .