Ultrasonic-assisted Brazing Research Articles

A Novel Diamond/AlSi Composite Coating on Ti-6Al-4V SubStrate Made by Ultrasonic-Assisted Brazing

Ultrasonic-assisted brazing (UAB) technology has been introduced to prepare the diamond/AlSi composite coating on Ti-6Al-4V substrate. The microstructure and wear properties of the coating were studied. The results showed that AlSi filler metal had a certain spreading and climbing phenomenon on the diamond surface, indicating a significant improvement in wettability between AlSi filler metal and diamond by ultrasonic-assisted brazing. Under ultrasound action, the microstructure of AlSi brazing alloy was greatly refined, and the Ti atoms in the Ti-6Al-4V substrate diffused to the interface between diamond and AlSi brazing alloy and formed TiC on diamond particles. There was no thermal damage to diamond particles when the brazing temperature was 750 °C. UAB improved the microhardness of the coating alloy matrix due to the increasing quantity and distribution range of TiAl3 as reinforced particles but had no obvious effect on the microhardness of the Ti-6Al-4V substrate. The wear resistance of Ti-6Al-4V substrate with diamond/AlSi composite coating was promoted due to the dense diamond particles, the formed TiC on diamond particles, and the increase in microhardness of the alloy matrix of diamond/AlSi coating under ultrasound action.

Study on effects of ultrasound on microstructure refinement at semi-solid statement of ultrasonic-assisted brazing SiCp/Al composites

Ultrasonic composite brazing uses ultrasonic cavitation and acoustic flow effects to ameliorate the soakage property of SiC particles and brazing material, enabling flux-free brazing of SiCp/Al-MMCs under atmospheric conditions. However, its mechanical properties are limited by the performance of the brazing material, which is often difficult to apply in structures with high strength requirements. In order to break through the limitations of conventional ultrasonic composite brazing of SiCp/Al-MMCs, this paper uses 50 vol.% SiCp/Al MMCs as base material and Zn-16Al brazing material. It applies secondary ultrasound at different times during the solidification of the liquid brazing material to reduce the weld grain size and reinforce the weld intensity by using ultrasonic cavitation and acoustic flow effects. The results show that the addition of secondary ultrasound can reduce the α-Al size and make the SiC particles and α-Al evenly distributed in the joint, which can significantly reinforce the intensity of the weld. The shear performance enhanced with the increase of supersound application second, but too long secondary sonication caused atomization of the brazing material, resulting in unfilled brazing material in the weld, which seriously affected the properties of the weld.

Reinforcement effect of Mg—Al—Zn ternary IMC on MB8/2024 joints with Al/Zn/Cu/Zn multi-interlayer via ultrasonic-assisted brazing

The evolution of microstructure in the MB8/2024 dissimilar alloy joints by using Al/Zn/Cu/Zn multi- interlayers via ultrasonic-assisted brazing was investigated. The results show that the addition of aluminum foil on the MB8 side realized the transformation of Al3Mg2 binary intermetallic compounds (IMCs) to AlMg4Zn11 ternary IMCs along the interface between copper foil and MB8 magnesium alloys. This transformation reinforced the joints and then the shear strength reached a maximum at 22 s (85.26 MPa). Thermodynamic analysis shows that ΔGMg,Al,Zn of AlMg4Zn11 (–38.65 kJ/mol) was smaller than that of Al3Mg2 (–31.94 kJ/mol), which provided a basis for the IMC transformation. Mg32(Al,Zn)49 quasicrystal was found for the first time using ultrasonic-assisted brazing due to the cavitation effect.

Effects of TiZn3 and TiZn16 components on the microstructure and mechanical performance of Ti-6Al-4 V alloy joints formed via ultrasonic assisted brazing using pre-galvanized workpieces

While the use of a Zn interlayer has been demonstrated to reduce the temperature required for joining easily oxidized metal alloys in atmospheric environments, the effects of reactions between the titanium alloy workpieces and the Zn interlayer on the mechanical performance of the finished joints are poorly understood. The present work addresses this issue by evaluating the chemical compositions at the interfaces of pre-galvanized Ti-6Al-4 V alloys joined at 420 °C in an atmospheric environment by ultrasonic-assisted brazing, and relating the observed compositions to the mechanical performances of the joints. The Ti-6Al-4 V alloy workpieces are first wetted by pure Zn using an ultrasonic assisted hot dip galvanizing (U-HDG). The obtained ultrasonic excitations are demonstrated to destroy the oxide film on the surfaces of the Ti-6Al-4 V workpieces and promote reactions between Ti and Zn at the interfaces. The plating of Zn on the workpiece surfaces is demonstrated to be realized by the formation of intermetallic compounds (IMCs) comprising a uniform TiZn3 layer in contact with the Ti-6Al-4 V surface, followed by a mixed TiZn3 + TiZn16 layer and a η-Zn layer at the outer surface. Application of the ultrasonic-assisted brazing process is demonstrated to maintain uniform TiZn3 layers next to the Ti-6Al-4 V surfaces, while the concentration of the TiZn16 phase near the midpoint of the joints increases with increasing ultrasonic treatment time (UST) from 5 s to 20 s, and the corresponding concentration of the η-Zn phase decreases. The results of mechanical testing demonstrate that the shear strength of the joint obtained with a TiZn3 layer thickness of 8–12 μm and a UST of 10 s is 210 MPa, which is 3.55 times greater than that obtained for joints processed without pre-galvanization.

Ultrasonic-Assisted Brazing of Titanium Joints Using Modified Al-Si-Cu Based Fillers: Brazing at Liquid—Semisolid States under Load

Brazing joints of Ti/Ti under ultrasonic vibration (USV) and compression load were investigated using optimized and modified filler alloys of Al-Si-Cu-(Ni)-(Sr) group prepared in the lab. Preliminary trails at semisolid to liquid states were conducted using the ready Al-Si-Cu-(Mg) alloy as a filler, then the brazing cycle was redesigned and enhanced according to the microstructural observations of the produced joints. USV assisted brazing at the semisolid state of low solid fraction was able to produce joints with round silicon morphology and granular α−Al, while at a high solid fraction, USV was only able to affect the silicon and intermetallic particles. Applying a compression load after ultrasonic vibration, at a designed solid fraction, was proved to be a successful technique for improving the quality of the joints by reducing the porosity, enhancing the soundness of the joint, and the diffusion at the interface. Based on alloy composition and the improved brazing cycle, joints of thin intermetallic layer and high shear strength (of 93 MPa average value) were achieved. The microstructures and the mechanical behavior were discussed based on the filler compositions and brazing parameters.

Ultrasonic-Assisted Brazing of Titanium Joints Using Al-Si Based Fillers: Numerical and Experimental Process Design

The ultrasonic-assisted brazing process was studied both numerically and experimentally. The ultrasonic brazing system was modeled by considering the actual brazing conditions. The numerical model showed the distribution of acoustic pressure within the filler and its variations according to the gap distance at different brazing temperatures. In the experimental part, brazing joints were studied and evaluated under multiple conditions and parameters. Although either the initial compression load or the ultrasonic vibration (USV) can initiate the interaction at the interface, the combined effect of both helped to produce joints of a higher quality with a relatively short brazing time, which can be further optimized in terms of their mechanical strength. The effect of the Si content on the joint interface, and the effect of the brazing conditions on the microstructures were studied and discussed.

Effect of Al–Si alloy coating on interfacial reactions and tensile strength in Ti/Al dissimilar brazing joints

Abstract We used ultrasonic-assisted brazing to join Al-Si-coated Ti alloys and Al alloys with a Zn-Al-Si filler metal. At the interface between the Ti alloy and Al-0.1Si alloy coating, a block TiAl3 phase formed. In contrast, for the Al-5Si alloy coating, the interfacial reaction layer of the joint consisted of a block Ti(Al,Si)3 phase and needle-like Ti7Al5Si12 phase. Finally, a granular Ti7Al5Si12 phase was formed at the joint interface for the Al-12Si alloy coating. The tensile strength of the joints formed with the Al-0.1Si and Al-12Si alloy coatings was only 160 -185 MPa, and cracks propagated mainly through the reaction layer. The tensile strength of the joints formed with the Al-5Si alloy coating ranged from 210 to 215 MPa, and cracks appeared entirely within the coating, subsequently expanding along the coating and ultimately resulting in failure of the joint.

Microstructure and Mechanical Properties of Ultrasonically Assisted Brazing of Dissimilar Cu–Al Alloys

An ultrasonic assisted brazing method, without flux and conducted in air, was developed to braze dissimilar copper-aluminum (Cu/Al) alloys. The microstructure and properties of Cu/Al joints of Sn–9Zn eutectic solder with different parameters were studied. The results show that the Intermetallic Compound (IMC) of the Sn–9Zn/Cu interface is mainly composed of Cu5Zn8 and Cu6Sn5. According to first-principles calculations, the covalent bond formed by Cu and Zn atoms in Cu5Zn8 is weak, whereas the covalent bond formed by Cu atoms and Sn atoms in Cu6Sn5 is strong. In the absence of ultrasonically assisted brazing, the shear performance of the joint at 220 °C is 21.8 MPa. At the same temperature, the performance of the joint with the ultrasonically bonded 10 s is 36.8 MPa, which represents an average increase of 68% compared to the non-ultrasonic welding joints.

Evolution of microstructure and phase composition of joints with ultrasonic-assisted resistance brazing

ABSTRACT Zn–2Al alloy is used as a filler metal for brazing of aluminium 6063 alloys by ultrasonic-assisted resistance brazing (RB) technology. The evolution of the microstructure and phase composition under the effects of the electric field and ultrasonic vibration were studied. The results show that ultrasonic cavitation can remove the existing oxide films effectively and inhibit element segregation, which help obtain joints with good metallurgical bonding. In comparison to RB joints, which exhibit a coarse dendritic structure, a uniform dendritic structure was obtained in the ultrasonic-assisted resistance joints. Furthermore, the combined electric and ultrasonic field has a significant effect on grain size and on dissolution during brazing. With the application of ultrasonic vibration, the diffusion between the base metal and the Zn–2Al filler metal intensifies.

Microstructure and strength of ultrasonic-assisted brazed joints of Si3N4/6061Al composites

The ultrasonic-assisted brazing of 30 vol.% Si3N4/6061Al composites in air using a filler metal comprising a Zn-Al alloy was investigated. Effects of the ultrasonic action duration and brazing temperature on the microstructure and mechanical properties of the brazed joints were focused on. The surface oxide layer between the composites and filler metals appeared to be broken and gradually removed by the ultrasonic action, and a composite bond with uniformly distribution of the reinforcements was formed eventually. As the ultrasonic action duration and brazing temperature increased, the proportion of Si3N4 particles and the atomic percentage of Al in the bond layer increased. Increasing the brazing temperature led to grain coarsening of the α-Al phase. The maximum shear bond strength of the joints was 183 MPa, and fracture occurred on the Al metal matrix composites side. The higher strength was attributed to the α-Al phase and Si3N4 particles being uniformly distributed in the bond layers.

Interfacial microstructure and mechanical properties of ultrasonic-assisted brazing joints between Ti–6Al–4V and ZrO2

Ultrasonic-assisted brazing (28.8 kHz, 180 W) was introduced to achieve high-quality joints between Ti–6Al–4V alloy and ZrO2 ceramic with Al-5wt.%Si brazing filler in air. The interfacial microstructure of intermetallic compounds (IMCs) and the phase constitution of joints ultrasonic-assisted brazed at 700 °C for different ultrasonic time were investigated in detail using a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer and X-ray diffractometer. When the ultrasonic time was 20s, the average shear strength of the joint reached a maximum value of 90.68MPa and two important types of IMCs Ti(Al,Si)3 and Ti7Al5Si12 formed at the interface between the Ti–6Al–4V and the filler. Ultrasonic played a vital role in the formation of Si segregation regions at the interface near the Ti–6Al–4V and in the centre of the joint. A change in the Ti molar fraction, resulting from the cavitation effect of ultrasonic on the surface of Ti–6Al–4V, increased the chemical potential gradient of Si across the joint. Meanwhile, driven by the ultrasonic standing wave field in the liquid Al-5wt.%Si filler, Si atoms moved to the ultrasonic antinode-plane spontaneously. Ultrasonic-assisted brazing proved to be an effective method of joining Ti–6Al–4V and ZrO2 with Al-5wt.%Si filler.

Formation and elimination of burst phenomenon in ultrasonic-assisted resistance brazing

A two-step ultrasonic-assisted brazing method and its associated apparatus were developed to make 6063 aluminum alloys joints with Al−Si−Mg filler metal. The burst phenomenon and the effect of ultrasonic direction and time, as well as the welding joint geometry on the burst phenomenon were investigated. The results show that the burst phenomenon occurs in the liquid filler metal under the effects of high current density, heat, and interaction force. The burst phenomenon is eliminated when the oxide film on the edge of the cross-section of the two parent metals is removed with more than or equal to 6 s ultrasonic time. A model of formation and elimination for burst was proposed, through which the blasting phenomenon can be controlled by changing the ultrasonic time and the geometrical shape of the welded joint.

Effect of ultrasonic vibration on wetting of water/Cu, water/PTFE, E-GaIn/Cu and E-GaIn/graphite

The wetting of atomic/molecular liquid under the ultrasonic vibration were studied for probing of the spreading driving force. Under the ultrasonic vibration, the wettability can be improved significantly. The momentum transfer at the liquid/solid interface can be a driving force for spreading, but it is invalid for the contact angles in a range near 90° for the non-wetting systems. The ultrasonic vibration induced the liquid/vapor interface roughening (i.e., the capillary wave at liquid/vapor interface) also can be a source of driving force. The spreading depended on the physic property of liquid, especially depended on the capillary wave on the surface of liquid. Therefore, in the application of ultrasonic-assisted brazing, the improved wettability by the ultrasonic vibration may be mainly caused by the mentioned physical factors rather than the chemical reaction at the liquid/solid interface.

Formation of amorphous interfacial layer between Zn-based alloy and SiC particles under ultrasonic-assisted brazing

Abstract The joining of an aluminium matrix composite to a titanium alloy by ultrasonic-assisted brazing using a Zn-based filler metal was investigated. An approximately 50-nm-thick amorphous Zn–Mg–Si interfacial layer formed between the Zn-based filler metal and SiC particles adjacent to the Ti alloy side of the brazed joint. Many of the Zn crystals that formed during brazing nucleated in this amorphous layer, suggesting that the amorphous layer acted as a diffusion layer between the Zn-based filler metal and SiC ceramic during brazing. This work not only explains the improvement in the performance of the brazing joints by the ultrasonic action but also proposes a strategy to optimise the interfacial structure for other metallic alloys.

High-performance joining technology for aluminium matrix composites using ultrasonic-assisted brazing

ABSTRACTHigh-performance aluminium matrix composite joints were fabricated using a new joining technology assisted by ultrasonic vibration. The performance of the joints was close to that of the parent materials. The microstructure and the mechanical performance were found to be systematically dependent on the volume fraction and the distribution of reinforcement particles in the bond region. The authors believe that this study can be generalised to the bonding of other ceramic-reinforced metal matrix composites.

Microstructure and mechanical performance of composite joints of sapphire by ultrasonic-assisted brazing

A method of lowering the coefficient of thermal expansion (CTE) of a bond metal of sapphire joints was examined for inhibiting the interfacial cracking of joints. An interlayer with the sandwich structure of Zn-Al/(SiCp/A356)/Zn-Al was fabricated and the surface of sapphire blocks was coated with a Zn-Al alloy by assistance of ultrasound. The assembly of sapphire and interlayer was brazed under the action of ultrasound. A metallurgical bond is performed between the sapphire and interlayer, and the composite material of SiCp/A356 is dissolved by Zn-Al alloys during brazing, resulting in a joint consisting of a new composite material of SiCp/Zn-Al-Si. It was composed of Zn-Al-Si alloy matrix and SiC particles with ∼40 vol.%, and has a CTE of ∼7.4 × 10−6 /°C estimated by using Turner’s model, approaching that of sapphire (∼5 × 10−6 /°C). The maximum shear strength of the composite joints reached ∼155 ± 10 MPa, an increase of ∼250% in comparison with that joined using the Zn-Al alloys.

Ultrasonic-assisted fluxless reactive bonding of Mg/Al dissimilar alloy using Zn–Al solder in air

ABSTRACTAn ultrasonic-assisted reactive brazing method, without flux and conducted in air, was developed to braze Mg/Al dissimilar alloys. By using pre-coated Zn–Al solders on the Al sheet and a short-time ultrasonic (3 s) assistance, the Mg/Al dissimilar sheets were successfully brazed at a low temperature (340°C). The effect of Al content of the solder on the shear strength was investigated based on the analysis of the microstructure and the fracture behaviour of the brazed joint. The results indicated that the microstructure and the shear strength of the ultrasonic-assisted brazed joint were significantly affected by Al content in Zn–Al solders. Increasing Al content in Zn–Al solder prevented the joint from forming the continuous brittle MgZn2 layer. The maximum shear strength of 110.5 MPa was obtained when Zn–15Al solder was used, because the joint possessed the optimum microstructure of the soft (Al, Zn) eutectoid matrix with the MgZn2 dispersed particles.

Overwhelming reaction enhanced by ultrasonics during brazing of alumina to copper in air by Zn-14Al hypereutectic filler

The ultrasonic-assisted brazing of α-alumina to copper was achieved in air without flux using Zn-14wt%Al hypereutectic filler at 753K within tens of seconds. The effects of ultrasonic time on the microstructures and mechanical properties of joints were investigated. In the joint interlayer, large amounts of intermetallic phases consisted of binary CuZn5 embedded by many ternary Al4.2Cu3.2Zn0.7 particles were formed. At the ceramic interface, newly formed crystalline Al2O3 aggregated. At the Cu interface, acoustic corrosion on the copper resulted in depriving the surface oxides and forming many pits on its surface, which provided saturated Cu in the melted filler alloys during the brazing. The ultrasonic vibrations had distinct effects on the metallurgical reactions of the joints, resulting in intermetallic-phase-filled composite joints with shear strength of 66MPa. The overgrowth of intermetallic compounds, the newly formed crystalline alumina, and the acoustic pits was probably ascribed to the ultrasonic effects.

WC particulate reinforced joint by ultrasonic-associated brazing of WC-Co/35CrMo

During the hybrid ultrasonic frequency induction brazing of tungsten carbide-cobalt/35CrMo (WC-Co/35CrMo) steel, a Ag-Cu-Zn-Mn-Ni metal was utilized as a filler metal, the vibration frequency was 21kHz, and the brazing temperature was varied from 710°C to 820°C. WC particles dispersed in the bond with the ultrasonic vibration, which phenomenon did not occur during traditional brazing processes. Based on the evolution of the microstructure of the WC particles in bonds formed at different ultrasonic times, the dissolution behavior of cobalt (Co) in Ag-based filler metal was investigated. A migration model of WC particles into the bonds was proposed that enables the control of the extent of reinforcing WC particles. Compared with conventional frequency induction brazing, WC particles in the bond via this ultrasonic-assisted brazing technique strengthened the joints significantly, resulting in a shear strength increase of 17% (approximately 408MPa).

Effect of ultrasonic transmission rate on microstructure and properties of the ultrasonic-assisted brazing of Cu to alumina

Fluxless brazing of bare alumina with Cu was conducted with an ultrasonic-assisted brazing technique by a Zn-14wt.%Al filler. The shear strength of Cu/alumina joints (84MPa) exhibited 27% larger than the alumina/Cu joints (66MPa) due to different intermetallic phases and their morphologies formed in the seam under the same parameters, which are probably attributed to the transmission rate of ultrasonic energy varying with density of the ultrasonic horn-contacted materials. Overgrowth of stalactite-like CuZn5 contributes to better thermal dissipation of the ultrasonic-assisted brazed Cu/alumina joints.