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In this work, porous Si 3 N 4 ceramics were successfully and ultrasonically soldered using Sn9Zn2Al solder through sonocapillary and cavitation. Si 3 N 4 ceramics were first ultrasonically wetted and then soldered. The results show that porous Si 3 N 4 ceramics can be wetted in the air within extreme short time of 10 s under ultrasonic. The capillary filling distance of the solder into the ceramic micro-channels achieves a value of 60 μm within 10 s and increases with prolonged ultrasonic time and high ultrasonic power. The infiltrated solder tightly bonded with the ceramic rod. The shear strength of the joint increases at prolonged ultrasonic time and becomes stable after 60 s. A geometric model is built to analyze the infiltration mechanism of the solder, and the result shows that the acoustic pressure inside the solder can reach 4 MPa, which is much higher than the pressure (0.32–1.4 MPa) needed for the sonocapillary action. The wetting mechanism of the solder to the ceramic is analyzed based on the cavitation bubble dynamics calculation. The high liquid velocity, pressure and temperature caused by the collapse of the cavitation bubble serve as the main factors that wet the ceramic. • Porous Si 3 N 4 ceramics are successfully and ultrasonically wetted and soldered by Sn9Zn2Al solder. • The joint can be obtained at a low temperature of 240 °C and short time of 10 seconds. • The solder infiltrates the ceramic through sonocapillary, and the mechanism is analyzed. • The wetting mechanism of solder to ceramic is studied based on the cavitation bubble dynamics calculation. [ABSTRACT FROM AUTHOR]

Abstract An ultrasonic-induced capillary action method was used to join porous ceramics for the first time. Results indicated that under ultrasonication, the solder infiltrated the porous ceramics and formed a soldered joint. The solder infiltration distance increased with prolonged ultrasonication time and reached 42 μm at an ultrasonication time of 120 s. Ceramic particles were eroded off and flowed into the joint seam because of the intense cavitation within narrow clearances. A fully penetrated layer formed near the joint seam at 120 s. This joint seam had high strength, so cracks propagated throughout the ceramic substrate during shear tests. Overall, our method was suitable for joining porous and microporous materials. Highlights • Porous ceramics were successfully joined by ultrasonic soldering. • Under ultrasonication, solder infiltrated the porous substrate to form a composite region. • Joint shear strength reached 33 MPa at 120 s, and crack propagated throughout the substrate. [ABSTRACT FROM AUTHOR]

Highlights • The physical process and mechanism of cavitation erosion during ultrasonic-assisted soldering were revealed. • Superior erosion effects were obtained using relatively high ultrasonic power and small channel width. • The incubation stage lasted shorter than 0.5 s at a channel width of 0.2 mm. • The removal of the oxide film mainly depended on the stable cavitation stage. Abstract Using pure Sn as filler metal, this study investigated cavitation erosion effects during ultrasonic-assisted soldering. The physical process and mechanism of cavitation erosion were revealed. Superior erosion effects were observed under long ultrasonic times, small channel widths, and high ultrasonic powers. Different vibration intensities were obtained inside filler pool. Region I, which was located far from the sonotrode, exhibited a stronger vibration intensity and better erosion effect than those of the other regions. The erosion incubation stage was shorted than 0.5 s at the channel width of 0.2 mm. Complete oxide layer removal was obtained at an ultrasonic time of 2 s under this condition. The violent cavitation stage was shorter than the erosion incubation stage, and the removal of the oxide layer mainly depended on the stable cavitation stage. [ABSTRACT FROM AUTHOR]

Highlights • Direct observation of cavitation phenomena during ultrasonic-assisted soldering was first recorded. • Numerous tiny transient bubbles dominated in the cavitation field and limited steady bubbles were observed. • Cavitation intensity decreased with ultrasonic time. • Stronger cavitation was observed when small channel width and large ultrasonic power were used. Abstract The cavitation characteristics at filler metal/substrate interface during ultrasonic-assisted soldering were first recorded by high-speed photography in this work. Two kinds of bubbles, steady cavitation bubbles and transient cavitation bubbles were observed. Steady cavitation bubbles did not collapse within one acoustic period and could last longer than 50 acoustic periods. Transient cavitation bubbles formed and collapsed within one acoustic period. The cavitation process was divided into two stages based on the cavitation characteristics. The first violent cavitation stage was in fact the degassing process, which lasted approximately 2700 acoustic periods and was affected by the gas content trapped inside the filler metal and the stronger vibration at the initiation stage of ultrasonic-assisted soldering. The second steady cavitation stage had obvious low bubble density and accounted for the most of the soldering process. Higher cavitation densities were observed when small channel width and large ultrasonic power were used because of larger sound pressures inside the filler metal. [ABSTRACT FROM AUTHOR]

In this work, an ultrasonic-assisted semi-solid brazing method was proposed to join Al/Mg. Oxide films on substrate surfaces can be successfully removed even when filler metal was at semi-solid state. A large quantity of intermetallic compounds (IMCs) formed at 460 °C because of large amount of Al and Mg dissolved into joint caused by strong cavitation. Decreasing the temperature to 430 °C could significantly reduce IMC. However, weak cavitation happened inside low liquid phase fraction at 420 °C, making it difficult to break IMCs and solid phases. [ABSTRACT FROM AUTHOR]

To prevent the formation of Al/Mg intermetallic compounds (IMCs) of Al 3 Mg 2 and Al 12 Mg 17 , dissimilar Al/Mg were ultrasonic-assisted soldered using Sn-based filler metals. A new IMC of Mg 2 Sn formed in the soldered joints during this process and it was prone to crack at large thickness. The thickness of Mg 2 Sn was reduced to 22 μm at 285 °C when using Sn-3Cu as the filler metal. Cracks were still observed inside the blocky Mg 2 Sn. The thickness of Mg 2 Sn was significantly reduced when using Sn-9Zn as the filler metal. A 17 μm Mg 2 Sn layer without crack was obtained at a temperature of 200 °C, ultrasonic power of Mode I, and ultrasonic time of 2 s. The shear strengths of the joints using Sn-9Zn was much higher than those using Sn-3Cu because of the thinner Mg 2 Sn layer in the former joints. Sn whiskers were prevented by using Sn-9Zn. A cavitation model during ultrasonic assisted soldering was proposed. [ABSTRACT FROM AUTHOR]

Joint seam is always the weak region of the welded joint. The soldered/brazed ceramic joint always fails through the joint seam due to lower strength of the solder/braze. In this work, to fabricate ceramic joint stronger than its substrate, ultrasonic vibration was used when brazing porous Si 3 N 4 ceramics. Results show that the brazing can be directly realized at 450 °C in air because ultrasonic cavitation can break the oxide layers of braze. Under ultrasonication, high acoustic pressure is obtained in braze, thus it rapidly infiltrates into the porous ceramics. Then, tight bond is realized between the ceramic and braze within several seconds because of the cavitation phenomenon. The transmission electron microscope results show that the main bonding medium at the ceramic/braze interface is an amorphous Al 2 O 3 layer. Shear test reveals that long ultrasonic time is beneficial to the shear strength of the joint. Wetting times longer than 10 s produce joint stronger than the ceramic substrate. This work provides a new insight when joining other porous materials. • Porous Si 3 N 4 ceramics joints stronger than the substrate was fabricated by ultrasonic brazing. • Short ultrasonic time of 10 s and low temperature of 450 °C produce joint stronger than the ceramic substrate. • The wetting interface is characterized by amorphous Al 2 O 3. [ABSTRACT FROM AUTHOR]

• Cavitation characteristics of GaIn melt during the ultrasonic-induced spreading process are studied in situ by high-speed photography. • The cavitation cloud, single cavitation bubble, stable cavitation bubble, their sizes and life periods are identified. • The bubble density decreases with the spreading of the droplet, which is explained by acoustic pressure. • A non-cavitation region showing increasing width as the droplet spreads consistently appears at the spreading front due to the acoustic pressure loss. • A cavitation threshold measuring method is proposed, and the cavitation threshold of eutectic GaIn alloy is identified to be approximately 0.65 MPa. Cavitation is widely used in many fields, but the nature of cavitation, especially in metallic liquids, remains unclear. In this work, the cavitation bubble characteristics during the spreading of eutectic GaIn liquid droplet subjected to ultrasonication were studied in-situ by high-speed photography. The types, diameters, variations, and life cycles of cavitation bubbles were identified. Results show that the bubble density gradually decreases during the droplet spreading process because of the decreased acoustic pressure inside the thinned liquid. The cavitation presents strong/weak change characteristics with a period of dozens of acoustic periods (T, 50 µs). Cavitation clouds with large sizes and long lifetimes are observed at the early-spreading stage. Tiny cavitation bubbles emerging and collapsing within 1 T dominate the cavitation field in the late-spreading stage. Stable cavitation bubble showing continuous nucleation and collapse but minimal changes in its position is also observed. A non-cavitation region consistently appears at the spreading front because the acoustic pressure is below the cavitation threshold. The width of the non-cavitation region gradually increased as the size of the spreading area increased. A cavitation threshold measuring method is proposed based on the cavitation observation and simulation and the cavitation threshold of eutectic GaIn alloy is identified to be approximately 0.65 MPa. The cavitation bubble dynamics result shows that the cavitation bubbles with different nucleation diameters have different life periods the same growth velocity. [Display omitted] [ABSTRACT FROM AUTHOR]

Highlights: [•] Vibration characteristics of the aluminum surface subjected to ultrasonic waves are shown. [•] The method to eliminate the presence of the zero-amplitude region on the base metal is proposed. [•] The response of liquid solder to the vibration of the base metal surface is presented. [•] The surface vibration of the base metal/liquid solder and the oxide film removal is correlated. [ABSTRACT FROM AUTHOR]

• The acoustic pressure of the solder was increased by four times when the width of the lap clearance was reduced from 0.8 mm to 0.2 mm. • Higher ultrasonic intensity gave rise of more eroded Al spots and grain refinements in the joint and produced stronger joint. • The rapid ultrasonic soldering process was discussed from the viewpoint of the effect of the collapse of cavitation bubbles. To avoid substrate softness, AA7075 were rapidly soldered using a Sn-9Zn solder at 200 °C under ultrasonication. The effect of acoustic intensity on the microstructure and mechanical properties of the soldered joint was studied. The acoustic intensity inside the solder was improved by decreasing the lap width without increasing the input ultrasonic power. Results showed that the softness of the substrate was almost avoided with minimal hardness decrease. The acoustic intensity increased by four times when the width of the lap clearance was reduced from 0.8 mm to 0.2 mm. Pronounced erosion of the substrate occurred under high acoustic intensity. Thus, the content of Al in the joint seam increased from 3.35% to 10.84% after reducing the lap width from 0.8 mm to 0.2 mm. The joint seam was characterized by interlaced fine/coarse Sn-Zn eutectic. The Sn and Zn grains had average sizes of 2.31 and 0.31 μm in the fine eutectic and 3.03 and 0.41 μm in the coarse eutectic. Increasing the acoustic intensity during soldering can effectively increase joint strength. The maximum shear strength of 65.4 MPa and hardness of 29.5 HV were obtained in the joint soldered at 0.2 mm. The cavitation bubble with a nucleation diameter of 10 μm had a large liquid velocity of 7653 m/s, a temperature over 1800 K, and a pressure of 4 × 1012 Pa during its collapse. [ABSTRACT FROM AUTHOR]

[Display omitted] • The cavitation characteristics of Sn melt during ultrasonic-assisted spreading are studied through high-speed photography. • The bubble density decreases with the spreading of the droplet, which is correlated by acoustic pressure simulation. • A noncavitation region at spreading front is responsible for the phenomenon that the oxide layer is difficult to remove. • A method of measuring the cavitation threshold of liquid metals through experiment and numerical simulation is proposed. • The cavitation threshold of pure Sn is first identified, which is 1.26 MPa at 250 °C. The cavitation characteristics during the spreading of a pure Sn liquid droplet subjected to ultrasonication were studied for the first time through high-speed photography to reveal the wetting mechanism. Ultrasonic vibration realized the spreading of Sn droplet on the nonwetting pure Al substrate. However, the oxide layer of the substrate at the spreading front is difficult to remove. The high-speed photography result shows that a noncavitation region consistently appears at the spreading front, because the acoustic pressure is below the cavitation threshold of 1.26 MPa. In particular, the width of the noncavitation region gradually increases as the size of the spreading area increases. Such a result accounts for the condition wherein the oxide layer at the spreading front is difficult to remove. Furthermore, the bubble density during spreading gradually decreases due to the decreased acoustic pressure of the thinned liquid. Finally, the bubble dynamics were calculated to verify the wetting mechanism. [ABSTRACT FROM AUTHOR]

• Thin liquid metal layer produces stronger cavitation with more uniform bubble size and distribution than bulk liquid. • Cavitation characteristics under different parameters are correlated with the acoustic pressure simulation results. • High acoustic pressure and strong cavitation can still be obtained at the weakly vibrated region. • High bubble growth speed of 16.8 m/s is obtained and evidenced by bubble dynamics calculation. Cavitation in thin layer of liquid metal has potential applications in chemical reaction, soldering, extraction, and therapeutic equipment. In this work, the cavitation characteristics and acoustic pressure of a thin liquid Ga–In alloy were studied by high speed photography, numerical simulation, and bubble dynamics calculation. A self-made ultrasonic system with a TC4 sonotrode, was operated at a frequency of 20 kHz and a max output power of 1000 W during the cavitation recording experiment. The pressure field characteristic inside the thin liquid layer and its influence on the intensity, types, dimensions, and life cycles of cavitation bubbles and on the cavitation evolution process against experimental parameters were systematically studied. The results showed that acoustic pressure inside the thin liquid layer presented alternating positive and negative characteristics within 1 acoustic period (T). Cavitation bubbles nucleated and grew during the negative-pressure stage and shrank and collapsed during the positive-pressure stage. A high bubble growth speed of 16.8 m/s was obtained and evidenced by bubble dynamics calculation. The maximum absolute pressure was obtained at the bottom of the thin liquid layer and resulted in the strongest cavitation. Cavitation was divided into violent and weak stages. The violent cavitation stage lasted several hundreds of acoustic periods and had higher bubble intensity than the weak cavitation stage. Cavitation cloud preferentially appeared during the violent cavitation stage and had a life of several acoustic periods. Tiny cavitation bubbles with life cycles shorter than 1 T dominated the cavitation field. High cavitation intensities were observed at high ultrasonication power and when Q235B alloy was used because such conditions lead to high amplitudes on the substrate and further high acoustic pressure inside the liquid. [ABSTRACT FROM AUTHOR]

In this work, TA15 joints reinforced in situ with TiAl 3 IMCs were successfully fabricated using pure Al filler by ultrasonic brazing. TA15 alloys were first wetted by pure Al with and without ultrasonication and then ultrasonically brazed. The wetting of Al to the TA15 alloy was realized by the formation of a TiAl 3 phase at the contacting interface. The complete wetting of the Al filler to the TA15 substrate was achieved at 20 min without ultrasonication. Ultrasonication significantly accelerated the wetting process, and the time required to achieve complete wetting was shortened to 10 s. During ultrasonic brazing, the formation of TiAl 3 in the joint mainly depended on the holding time. The content of the TiAl 3 phase increased from 35.2% to 77.2% as the holding time was increased from 5 min to 30 min. Joint strength increased with the amount of TiAl 3 in the joint. Ultrasonication for 10 s and a holding time of 30 min generated a joint filled with homogeneously distributed TiAl 3. The maximum shear strength of this joint was 140.6 MPa, which was 75% higher than that of pure Al. Failure crack propagated through the filler at short holding times and through the filler and TiAl 3 phase at prolonged holding times. • TiAl 3 reinforced TA15 joints were fabricated by ultrasonic brazing with Al filler. • Complete wetting of Al to TA15 was accomplished within 10 s by ultrasonication. • The formation of the TiAl 3 phase mainly depended on the holding time. • 77.2% vol. TiAl 3 reinforced joint yielded maximum shear strength of 140.6 MPa. [ABSTRACT FROM AUTHOR]

• Intensified cavitation within narrow channel lead to significant grain refinement of the joint. • Cavitation-induced instant nucleation of Sn was mainly responsible for the grain refinement. • Soldered joint strength increased 65.4% when the grain size decreased from 2.62 µm to 1.04 µm. In this work, grain refinement of the aluminum soldered joint was obtained by applying cavitation within narrow channels and the possible grain refinement mechanism was proposed. Aluminum sheets with different channel widths were ultrasonically soldered by pure Sn in air. An ultrasonic system with a TC4 sonotrode, was operated at a frequency of 20 kHz and power of 1000 W during soldering. The effect of channel width on grain size, element distribution and strength of the soldered joint was studied. Results showed that the grain size decreased from 2.62 to 1.04 µm and the element ratio of Al in solder increased from 0.93 to 4.86% when the channel width decreased from 0.8 to 0.2 mm. Instant solidification of Sn grains was readily observed in the joint before cooling due to the large undercooling induced by the intensified cavitation inside the narrow channels. The random cavitation induced nucleation of Sn was believed to be mainly responsible for the grain refinement of the soldered joint. The shear strength of the joint increased from 29.5 to 48.8 MPa and the hardness increased from 16.5 to 25.2 HV due to the grain refinement of Sn and the presence of Al transferred from the substrates. [ABSTRACT FROM AUTHOR]

Carbon fiber reinforced aluminum matrix composites (C f /Al) are widely used in various industries. But they are difficult to join because it is hard to realize the wetting and continuity of the carbon fiber in joint. To solve this problem, C f /Al are joined by ultrasonic soldering in this work. Results show that the C f /Al can be wetted within 5 s under ultrasonic. Transmission electron microscope result shows that the surface of the wetted carbon fiber is covered by an amorphous-nanocrystalline layer, which is formed due to the high solder velocity, temperature and pressure caused by cavitation. Carbon fibers flow into the solder after the Al matrix is eroded, guaranteeing its continuity in the joint. Limited carbon fibers flow into the joint at low ultrasonic power of 333.3 W, while a fully carbon fiber reinforced composite joint is obtained at 1000 W. The soldered joints have higher strength than the C f /Al substrate, and its formation mechanism is discussed. [ABSTRACT FROM AUTHOR]

Porous Si 3 N 4 ceramics are widely used materials but very difficult to join. In this work, we successfully ultrasonically soldered porous Si 3 N 4 ceramic rapidly at a low temperature of 230 °C. The wetting and bonding mechanism at the ceramic/solder interface was studied. Results showed that the solder rapidly infiltrated the micro-channels of the ceramic during soldering, and high ultrasonic power contributed the sonocapillary distance. Zn and O acted as the main bonding elements. Bonding was realized by the formation of nanocrystalline and amorphous ZnO x region at the wetting interface. Rapid bonding was achieved due to the high liquid velocity, high temperature, and high pressure caused by the collapse of the cavitation bubbles. [Display omitted] • Porous Si 3 N 4 ceramics are successfully soldered within 10 s at 230 °C with the assistance of ultrasonic. • The solder rapidly infiltrates the ceramics through sonocapillary, the infiltration layer widens at high ultrasonic power. • Nanocrystalline and amorphous ZnO x formed at the wetting interface, and the wetting of solder to Si 3 N 4 is achieved. • The wetting mechanism is explained from the viewpoint of bubble dynamics. [ABSTRACT FROM AUTHOR]

Abstract: Power ultrasonic vibration (20kHz, 6μm) was applied to assist the interaction between a liquid Al–Si alloy and solid Ti–6Al–4V substrate in air. The interaction behaviors, including breakage of the oxide film on the Ti–6Al–4V surface, chemical dissolution of solid Ti–6Al–4V, and interfacial chemical reactions, were investigated. Experimental results showed that numerous 2–20μm diameter-sized pits formed on the Ti–6Al–4V surface. Propagation of ultrasonic waves in the liquid Al–Si alloy resulted in ultrasonic cavitation. When this cavitation occurred at or near the liquid/solid interface, many complex effects were generated at the small zones during the bubble implosion, including micro-jets, hot spots, and acoustic streaming. The breakage behavior of oxide films on the solid Ti–6Al–4V substrate, excessive chemical dissolution of solid Ti–6Al–4V into liquid Al–Si, abnormal interfacial chemical reactions at the interface, and phase transformation between the intermetallic compounds could be wholly ascribed to these ultrasonic effects. An effective bond between Al–Si and Ti–6Al–4V can be produced by ultrasonic-assisted brazing in air. [Copyright &y& Elsevier]