Fluxless Brazing Research Articles

Fluxless brazing of aluminium alloys by brazing filler metal of Al-Ge system

Fluxless brazing of aluminium alloys by brazing filler metal of Al-Ge system

Fluxless Brazing of aluminum alloys using non vacuum electron beam by 60kV acceleration voltage

Lightweight construction materials, in particular aluminum alloys, have recently become more important as construction materials due to their low weight with high strength and sufficient wear and corrosion properties. In order to be able to use the advantages resulting from the use of aluminum alloys, powerful and reliable thermal joining methods are required which reduce the heat input into the component and thus the distortion and change the set structure as less as possible. New approach here is the NV-EB brazing at low acceleration voltage. In particular, two aspects must be solved for process-reliable brazing of aluminum alloys. On the one hand, the oxide layer on the surface of the aluminum workpiece must be removed. On the other hand, sufficient heat must be put into the solder and base material in order to both melt the solder and to heat the base material sufficiently, but below the solidus temperature. Often the “Nocolok” potassium tetrafluoroaluminate flux is used. In addition, the harmful to health cesium fluoroaluminate and mixtures of both fluxes are used. Apart from health aspects, the use of fluxes has led to increased pollution of an equipment and corrosion, which contributes to process instability. By reason of described above, the investigation of a fluxless brazing of aluminum alloys using non vacuum electron beam by 60kV acceleration voltage is of great interest.

Ultrasound-induced liquid/solid interfacial reaction between Zn-3Al alloy and Zr-based bulk metallic glasses

Ultrasound-assisted fluxless brazing of Zr based Bulk metallic glasses (Zr-BMG) joint using Zn-3Al filler metal was performed in this study. The effect of ultrasonic vibration time on the microstructure and mechanical properties of Zr-BMG joints were investigated. Results showed that excellent metallurgic bonding could be obtained in ultrasonically brazed Zr-BMG joints. The interfacial reaction between liquid Zn-3Al filler metal and Zr-BMG substrate showed a mutation characteristic, which could be distinguished into incubation period and acceleration period. In the incubation period, Zn50Zr25Al25 intermetallic compounds (IMCs) with small ellipsoidal shape were slowly formed and distributed randomly on Zr-BMG surface. However, in the acceleration period, Zn50Zr25Al25 ellipsoids developed rapidly into a wavy-structured IMCs layer with a thickness of 17 μm, which was comprised of alternate Zn50Zr25Al25 and Zn22Zr sublayers. The microstructure evolution of Zn-3Al/Zr-BMG interface was ascribed to the combined effects of acoustic cavitations and Al element controlled interfacial metallurgic reactions. The average shear strength of joint was increased firstly then decreased slightly with increasing ultrasonic vibration time, and a highest strength value of approximately 100 MPa was obtained for joints brazed for 96 s. The shearing failure was inclined to occur at the Zn-3Al/Zr-BMG interface then transferred into the interfacial IMCs layer with increasing ultrasonic vibration time.

Feasibility study of fluxless brazing cemented carbides to steel

One of the most important brazing processes is the joints between cemented carbides and steel for the tool industry such as in rotary drill hammers or saw blades. Even though this technique has already been used for several decades, defects in the joint can still occur and lead to quality loss. Mostly, the joining process is facilitated by induction heating and the use of a flux to enhance the wetting of the filler alloy on the surface of the steel and cemented carbide in an ambient atmosphere. However, although the use of flux enables successful joining, it also generates voids within the joint, which reduces the strength of the connection while the chemicals within the flux are toxic and polluting. In this feasibility study, a fluxless brazing process is used to examine the joint between cemented carbides and steel for the first time. For this, ultrasound is applied during induction heating to enable the wetting between the liquid filler metal and the surfaces of the cemented carbide and steel. The ultrasound generates cavitations within the liquid filler metal, which remove the oxides from the surface. Several filler metals such as a silver based alloy Ag449, pure Zn, and an AlSi-alloy were used to reduce the brazing temperature and to lower the thermal residual stresses within the joint. As a result, every filler metal successfully wetted both materials and led to a dense connection. The ultrasound has to be applied carefully to prevent a damage of the cemented carbide. In this regard, it was observed that single grains of the cemented carbide broke out and remained in the joint. This positive result of brazing cemented carbides to steel without a flux but using ultrasound, allows future studies to focus on the shear strength of these joints as well as the behavior of the thermally induced residual stresses.

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.

최신의 고능률 브레이징 기술개발 동향

Recent developing tendency for technologies of high efficient brazing are studied by searching of NDSL, Science Direct, KIPRIS, PCT and so on. Active metal brazing, arc brazing, fluxless brazing, brazing with low melting point, reactive air brazing, laser brazing, laser droplet brazing are investigated. By optimal selecting of the above mentioned technologies, it needs to investigate an economical metallurgical design and the advanced brazing methods. To improve the embrittlement of intermetallic compound at brazing interface, it must be studied the inexpensive variant metals including nonmetals and the heat sources(MIG, TIG, Laser) by hybrid techniques. Key words: Brazing, fluxless brazing, Laser brazing, Active metal, Laser droplet, Intermetallic compound

Interfacial reaction behavior and mechanical properties of ultrasonically brazed Cu/Zn–Al/Cu joints

Abstract Ultrasound-assisted fluxless brazing of Cu/Zn–Al/Cu joint was performed in this study. Evolutions of the microstructure and mechanical properties of Cu alloy joints ultrasonically brazed with Zn–3Al and Zn–14Al filler metals were investigated. Results showed that excellent metallurgic bonding between the Zn–3Al filler metal and the Cu substrate could be obtained by brazing at 450 °C for 4 s, accompanied with the creation of thick CuZn 5 and Cu 5 Zn 8 intermetallic compounds (IMCs) layers on the Zn–3Al/Cu interface. Compared with the Zn–3Al/Cu system, much longer ultrasonic vibration time was needed for the completely wetting of the Zn–14Al filler metal on the Cu substrate, but the thick Cu 5 Zn 8 IMC layer was replaced with a thin Cu based diffusion layer on the Zn–14Al/Cu interface. The wetting of Zn–3Al filler metal on the Cu substrate was attributed to the combined effects of ultrasound-induced cavitation and Cu/Zn metallurgic reaction, while the wetting of Zn–14Al filler metal on the Cu substrate was mainly attributed to the ultrasound-induced cavitation effects. The shear strength of the Cu/Zn–3Al/Cu and Cu/Zn–14Al/Cu joint was 37.9 MPa and 92.1 MPa, respectively; the shearing failure took place within the Cu interfacial layer in all case.

In Situ Measurement of the Thermal Contact Resistance of an Al Lap Joint During Braze Processing

A technique was developed, using a laser flash thermal diffusivity apparatus, to measure the thermal contact resistance, Rc, of an Al lap joint during braze processing. The method required a determination of the temperature dependence of the thermal diffusivity of the individual Al braze sheets, as well as a two-layer lap joint made from these sheets, under identical conditions. A two-layer modeling method was then used to analyze the above data to determine Rc for the lap joint as a function of processing temperature. This in situ analysis of Rc for a developing joint during brazing was able to distinguish both solid-state and liquid-phase reactions occurring at the faying surfaces of the joint. Consequently, it represents a powerful, new experimental tool that can be used to investigate the mechanisms of braze joint formation and the thermal properties of a joint as a function of processing condition. In the particular case of this study, the technique demonstrates that the use of a Ni-based fluxless brazing process to join aluminum (Al) sheets, reduced the Rc of the lap joint by 100-folds from 1.3 × 10−4 m2 K/W before brazing to 1.35 × 10−6 m2 K/W after brazing.

Physico-Chemical Aspects of Surface Activation during Fluxless Brazing in Shielding-Gas Furnaces

Continuous process brazing in shielding-gas furnaces is tailor-made for manufacturing mass production components by means of brazing technology. Which brazing tasks can actually be carried out by a shielding-gas furnace, depend on many ancillary conditions. In particular these are, besides the component size and joint geometry, the base materials and brazing filler metals as well as the material specific process parameters which are to be maintained in a continuous furnace in order that a process assured brazing can be guaranteed. In this context, the activation of the component's surfaces play a central role for wetting with the braze melt. Within the scope of this contribution, the variables and ancillary conditions concerning this matter are presented and discussed using the brazing process on stainless steels as an example.

Fluxless laser brazing of aluminium alloy to galvanized steel using a tandem beam – dissimilar laser brazing of aluminium alloy and steels

Tandem beam brazing with aluminium filler metal (BA4047) was conducted in order to develop the fluxless laser brazing technique of aluminium alloy (AA6022) to galvanized steels (GA and GI steels). Laser powers of tandem beam and offset distance of preheating beam from the root to the steel base metal were varied. Sound braze beads could be obtained by optimizing the preheating and main beam powers under the offset distances of 0–1 mm. A small amount of zinc remained at the braze interface between galvanized steels and the braze metal. The reaction layer consisting of Fe–Al intermetallic compounds was also formed at the steel interface, and the thickness of reaction layer could be predicted during the laser brazing (thermal cycle) process based on the growth kinetics with the additivity rule. The metal flow analysis of the melted filler metal on joints revealed that wettability and spreadability of the filler metal on the GI steel joint were superior to those on the GA steel joint. The fracture strength of the lap joint attained approx. 55–75% of the base metal strength of aluminium alloy. It was concluded that fluxless laser brazing could be successfully performed by using a tandem beam because the zinc coat layer acted as the brazing flux.

Ecologically clean technology of fluxless brazing of aluminium alloys

Ecologically clean technology of fluxless brazing of aluminium alloys

Principles of brazing

Principles of Brazing is a valuable resource for those working with the brazing process or designing component joints. This book will help solve practical engineering challenges, by building on fundamental metallurgy. Precisely written, and well referenced, containing 200 figures and 56 tables, this book compares joining methods, explains the fundamental parameters of brazes, and surveys the metallurgy of braze alloy systems. The joining atmosphere, fluxes and fluxless brazing are investigated. The constraints that component metal and non-metal materials place on the brazing process are examined. A chapter is devoted to the direct brazing of non-metals. Jewelers will find the chapter on filler metals for gold and silver of interest. The authors received valuable feedback from readers of their first book, Principles of Soldering and Brazing.

Fluxless Brazing of Al6061 Alloys Using Ag-28Cu Insert

A diffusion brazing of aluminium alloy A6061 was preformed using a Ag-28Cu insert to conduct eutectic brazing. Interface behaviors of the brazed joints were observed after brazing at 450-560°C. The tensile property of the brazed joints was also examined. During diffusion brazing of Al6061 alloys with Ag-28Cu insert, eutectic melts were formed by eutectic reaction between Al6061 and Ag-28Cu insert. It was found that the reaction layers composed of two phases were formed at the interface between Al6061 and Ag-28Cu insert. EPMA analysis revealed that two phases in the reaction layers consist of Ag-rich phase and Cu-rich phase. The tensile strength of the joints brazed at 560°C for 30min was 160 MPa.

Examination of the feasibility of fluxless brazing titanium pipelines

Examination of the feasibility of fluxless brazing titanium pipelines

New filler metals and process for fluxless brazing of aluminium engineering alloys

Many high strength aluminium engineering alloys cannot be joined by brazing because they either degrade or melt at the temperature at which commercially available aluminium brazes are used. A brazing process suitable for joining aluminium engineering alloys has been developed employing two novel low melting point brazes. The brazes are available as ductile foil preforms. The process is fluxless and no post-joining cleaning treatments are necessary. The aluminium components and the brazing foil require a simple chemical treatment before use. The brazing process is tolerant and can be satisfactorily implemented by heating to a temperature of 510–550°C, maintained for a period of 5–45 min, in either vacuum or a furnace chamber that is purged continuously with nitrogen gas. The joints exhibit high strength and adequate resistance to corrosion for most applications. Some promising new applications for aluminium brazing technology based on this new process are described.MST/3183

３００４合金の長時間フラックスレスろう付試験

Long time fluxless brazing tests on 3004 alloy and 3003 and high purity Al-1Mn-1Mg alloys for comparison were carried out mainly in vacuum (2×10-5torr) at 590 to 600°C using a BA 4004 clad brazing sheet. 3003 base metal has long time brazability superior to 3004 base metal. The fillet on 3003 base metal disappears after brazing for 180min at 600°C. While high purity Al-1Mn-1Mg alloy shows sufficient fillet after brazing for 180min, which confirms that the use of pure base metal is markedly effective to improve long time brazability of Al-Mn-Mg alloy. A decrease in mechanical strength of 3004 base metal is responsible to Mg vaporization during vacuum brazing. The decrease in strength is prevented a little by the carrier gas brazing method (N2 gas: 10-1torr).