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Aiming at the problem of porosity in laser brazing of galvanized sheet, three-spot laser brazing technology was used to solve the problem of pores caused by evaporation of zinc vapor. The surface morphology and mechanical properties of galvanized sheet laser brazed joints with or without three spots were studied. The results showed that when the three-spot laser brazing technology was applied, the zinc coating on the surface of galvanized steel was removed by coating removal laser in advance, zinc vapor escaped completely, and there were no visible pores on the surface of the weld. For the tensile strength and microhardness of brazed joints, when the laser power was 2500-3200 W, the welding speed was 40-50 mm/s, the wire feeding speed was 3.0-3.5 m/min, and the beam-spot size was 4.2-5.5 mm; the tensile strength of the brazed joint reached more than 80% of the base metal. The tensile strength of the brazed joint was sensitive to welding speed. The microhardness of fusion zone was higher than base metal, and the microhardness reached 120 HV. [ABSTRACT FROM AUTHOR]

Abstract Over the last 20 years, industry interest in copper has increased. Its application in the petrochemical, automotive, and nuclear power industries highlights the need for new research directions especially in the joining of copper to other metals. In this work, lap joint of 304 stainless steel and T2 copper precoated with Cu–Mn–Ni filler metal was performed by laser brazing. The aim of this study is to characterize the influence of laser beam incidence angle on the welded joint forming mode, microstructure, elements diffusion and corrosion resistance. According to the findings, the joint is classified as a welded joint when the laser beam incidence angle is 80°, and as a welded-brazed joint when it’s 90°, 70°, or 60°. The microstructure is mainly composed of Cu-rich and Fe-rich phases, Mn in the Cu-rich phase aggregation and Cr in the Fe-rich phase aggregation. In the fusion zone (FZ) the content of less than 50% of the liquid will be in the form of supersaturated droplets in the matrix of the other side. The local corrosion pair that the copper steel matrix and liquid drop produce in the FZ speeds up the dissolution of the Cu-rich phase, which effected corrosion resistance of the joint.

Over the last 20 years, industry interest in copper has increased. Its application in the petrochemical, automotive, and nuclear power industries highlights the need for new research directions especially in the joining of copper to other metals. In this work, lap joint of 304 stainless steel and T2 copper precoated with Cu–Mn–Ni filler metal was performed by laser brazing. The aim of this study is to characterize the influence of laser beam incidence angle on the welded joint forming mode, microstructure, elements diffusion and corrosion resistance. According to the findings, the joint is classified as a welded joint when the laser beam incidence angle is 80°, and as a welded-brazed joint when it’s 90°, 70°, or 60°. The microstructure is mainly composed of Cu-rich and Fe-rich phases, Mn in the Cu-rich phase aggregation and Cr in the Fe-rich phase aggregation. In the fusion zone (FZ) the content of less than 50% of the liquid will be in the form of supersaturated droplets in the matrix of the other side. The local corrosion pair that the copper steel matrix and liquid drop produce in the FZ speeds up the dissolution of the Cu-rich phase, which effected corrosion resistance of the joint. [ABSTRACT FROM AUTHOR]

The demand for steel/aluminum alloy dissimilar joints has increased for light-weighting the automobile body. However, it is well known that joining both metals by conventional welding methods, the brittle intermetallic compound (IMC) is generated at the interface, and it significantly deteriorates the joint strength. In this paper, the hot-wire laser brazing process using the twin-spot irradiation was proposed and its conditions were optimized to achieve the high brazing speed and the high joint strength on a lap-fillet joint of the steel/aluminum alloy dissimilar combination. The twin spots of a circle (ϕ5) and rectangular (5 × 11) laser beams aligned at spot ends achieved the high brazing speed up to 6 m/min, stable brazing phenomena and sound bead appearance. The joints fabricated using the optimized conditions realized the very thin IMC thickness under 2 μm and high joint strength over the yield strength of the base steel sheet. [ABSTRACT FROM AUTHOR]

Laser processing has its advantages of high energy density, good controllability, and high flexibility; it has shown its importance in advancing modern manufacturing. Laser processing is used in this paper to fabricate an end grinding wheel with orderly arranged abrasive particles, and the performance of the fabricated grinding wheel is compared with that of a conventional grinding wheel. Our experiment and comparative studies have drawn the conclusions of (1) active laser brazing has been successfully used to arrange diamond particles in Archimedes' spirals; (2) the resulted grinding wheel has shown the enhanced effectiveness in comparison with the conventional grinding wheel in terms of reduced grinding force; when the spiral change rate i is set 0.25, the tangential grinding force has been reduced by up to 60%; (3) for a grinding wheel with specific spiral change rate, ground debris are discharged from the grinding zone in a certain direction, and the grinding temperature can be reduced; (4) in high-speed grinding, the surface quality by the grinding wheel with orderly arranged abrasive particles is better than that of conventional grinding wheel; under the tested grinding conditions, the roughness of the ground surface has been reduced up to 47% of that by conventional grinding wheels; (5) the grinding wheel with orderly arranged abrasive particles has shown the better wear resistance that conventional grinding wheels; abrasive particles of all four conventional grinding wheels are damaged to certain extent but orderly arranged abrasive particles on the fabricated wheel maintain mostly their protruded heights. [ABSTRACT FROM AUTHOR]

Copyright of Automobile Technology & Material is the property of Automobile Technology & Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The trend is shifting from internal combustion engines (ICEs) to battery electric vehicles (BEVs). One of the important battery joints is battery tabs to the busbar connection. Aluminum (Al) and copper (Cu) are among the common materials for busbar and battery tab manufacturing. A wide range of research shows that the laser welding of busbar to battery tabs is a very promising technique. It can enhance the battery module's safety and reliability owing to its unique properties. The desired strength, ductility, fatigue life as well as electrical resistivity are crucial to attain in laser welding of dissimilar materials aluminum and copper in busbar to battery tab in BEVs. Therefore, an adequate understating of the principal factors influencing the Al–Cu busbar to battery tabs joint properties are of prime importance. The current review paper provides information on laser welding and laser brazing of dissimilar Al–Cu with thin thicknesses. Also, the common defects, the effect of materials properties on laser joining, and laser-materials interaction during the laser welding process are discussed. Laser process parameters adjustment (e.g., laser power or speed), laser operational mode, and proper choice of materials (e.g., base metals, alloying elements, filler metals, etc.) may enhance the joint properties in terms of mechanical and electrical properties.

Titanium and steel are widely used in “land, sea, air and space” fields. Due to the difference in physical and chemical properties of titanium and steel, a large number of brittle intermetallic compounds are often formed at the interface, which limits their wide applications. Based on the analysis of titanium/ steel dissimilar material welding, the laser brazing process and self-developed AgCuTiZr brazing alloy was used to carry out an investigation of titanium/ steel connection. Experimental results show that this active brazing alloy has good wettability to the matrix material, the microstructure of brazed layer is compact with a smooth surface. The active elements are diffused at the bonding interface, multiple phases coexist in the brazing layer, and chemical metallurgical bonding is realized between interfaces. The brazed layer of active AgCuTiZr alloy possess high hardness, which is 1. 5 times that of the base materials. The wear resistance of the AgCuTiZr brazed alloy is basically the same as that of the connecting material 45 steel / TA2, while tensile strength of the brazed layer is 595 MPa, which realized the reliable connection of the two materials. The obvious advantages of laser heat source are suitable for brazing of Heterogeneous metal materials. [ABSTRACT FROM AUTHOR]

Copyright of Automobile Technology & Material is the property of Automobile Technology & Material Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The wear resistance of laser brazing diamond coating with and without pre-machining V-groove on the diamond surface was investigated. The size of V-groove at the surface of diamond machined by laser was about 60°, and the edge length was around 120°. The wear loss of V-groove diamond brazing coating was smaller than that of noncut diamond brazing coating under the same laser power and friction load conditions. Thus, the wear resistance was significantly improved by pre-machining V-grooves on the diamond surface using laser. The V-groove is functioned as a 'rivet' diamond particles, greatly enhancing the diamond's anti-spalling performance throughout the wear process. Moreover, the wear loss of diamond brazing coating fabricated by laser power of 1.1 kW was smaller than that of 1 kW laser power. The wear loss of laser brazing coating is increased as the load is increased. [ABSTRACT FROM AUTHOR]

The temperature of laser brazing diamond seriously affects the quality and service life of diamond tools. In this study, a finite element model of laser brazing diamond was established to achieve digital control of the temperature field during the brazing process. It was determined that the main energy of diamond warming comes from the heat conduction of the molten pool. The maximum temperature value within the brazing layer was proposed as an important indicator of the quality of diamond coating formation. The correlation and local sensitivity of each process parameter to the maximum value of temperature were calculated by a neural network-based machine learning method, and the influence of process parameters on the temperature field was explored. The result of the theoretical analys was finally verified by the coating wear-resistance experiments, and the wear-resistance of the diamond coatings was significantly better than that of other cases when the maximum temperature value in the brazing process was in the range of 1100 °C–1130 °C. [Display omitted] • A finite element model was established to achieve digital control of the temperature field. • The correlation of P , v , r to Tmax was calculated using neural network-based machine learning. • The diamond coating exhibits superior wear resistance when Tmax is between 1100 and 1140 °C. [ABSTRACT FROM AUTHOR]

• A good brazed joint was successfully achieved under optimized parameters. • The strengthening mechanism of the brazed joint has been revealed. • It may be a good means to improve joint quality in car body manufacturing. In this study, hot-dip galvanized steel sheet was joined in a flange butted configuration using laser brazing with CuSi 3 filler metal. An orthogonal test involving four factors and five levels was experimentally designed to ascertain the optimal parameters and analyze the impact of welding factors on weld characteristics. The morphology, microstructure and mechanical property of laser brazed joints were carefully investigated using an optical microscope, scanning electron microscope equipped with energy spectrum analysis and other methodologies. The results showed that a joint with good forming quality was successfully achieved under the optimized brazing parameters. Welding speed was the most important factor affecting weld cross-section difference in the width, followed by defocusing amount, laser power and feeding speed. The microstructure near the fusion line was transformed from fine equiaxed grains to coarse columnar grains due to the fast cooling rate of the molten pool during solidification. The formation of wedge-shaped structures played a pinning role, which greatly enhanced the binding force at the interface. It has been also found that the occurrence of the composition segregation in the brazed joint increased the cracking susceptibility, thereby lowering the load capacity of the joint. The tensile strength of improved joints was obviously higher than that of the base metal. It was mainly credited to good surface forming and pinning effect of wedge-shaped structures under the optimized conditions. [ABSTRACT FROM AUTHOR]

The trend is shifting from internal combustion engines (ICEs) to battery electric vehicles (BEVs). One of the important battery joints is battery tabs to the busbar connection. Aluminum (Al) and copper (Cu) are among the common materials for busbar and battery tab manufacturing. A wide range of research shows that the laser welding of busbar to battery tabs is a very promising technique. It can enhance the battery module's safety and reliability owing to its unique properties. The desired strength, ductility, fatigue life as well as electrical resistivity are crucial to attain in laser welding of dissimilar materials aluminum and copper in busbar to battery tab in BEVs. Therefore, an adequate understating of the principal factors influencing the Al-Cu busbar to battery tabs joint properties are of prime importance. The current review paper provides information on laser welding and laser brazing of dissimilar Al-Cu with thin thicknesses. Also, the common defects, the effect of materials properties on laser joining, and laser-materials interaction during the laser welding process are discussed. Laser process parameters adjustment (e.g., laser power or speed), laser operational mode, and proper choice of materials (e.g., base metals, alloying elements, filler metals, etc.) may enhance the joint properties in terms of mechanical and electrical properties. [ABSTRACT FROM AUTHOR]

Copyright of Light Industry Machinery is the property of Light Industry Machinery Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

An attempt to increase the strengths of bonding between diamond and filler metal in producing high-precision machining tools was made in this paper by proposing new ultrasonic-assisted laser brazing (UALB) technique in which the UALB process was performed using a fiber laser and Ni–Cr filler alloy, followed by the paraxial feeding of diamond powder. In addition, to examine the impact of an ultrasonic vibration on the mechanical properties of diamond at its bonding interface, the brazing process was carried out with and without suppression in ultrasonic vibration, and the microstructure and mechanical properties of diamond at the bonding interface were observed, measured and compared. The results showed that the ultrasonic assistance had improved the strengths of the bonding of diamond with the filler alloy by reducing surface cracks, increasing the wettability of molten filler, and forming and crystalizing directional carbides of Cr 3 C 2 and Cr 7 C 3 with a higher density. [ABSTRACT FROM AUTHOR]

Brazing is a 5000 year old joining process which faced still with the advanced joining challenges that exist today [1]. In laser brazing components are joined together by heating above the melting point of a filler metal placed between them. It provides unique advantages over other joining methods, including the ability to joint dissimilar material. Indirect laser brazing is a novel process which able to joint dissimilar metals with minimal formation of a brittle intermetallic compound (IMC) layer than conventional furnace brazing. In this study the viability of indirect laser brazing process was investigated between Ti6Al4V and 316L stainless steel. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Laser keyhole brazing is an opportunity to increase the process efficiency in laser brazing processes. Using small spot sizes increases the intensity and leads to the formation of a vapour capillary (keyhole) in the brazing material when a material-specific threshold value is exceeded. Due to multiple reflections/absorptions of the laser beam in the keyhole, the process efficiency increases in comparison with conventional brazing processes with single Fresnel absorption on the surface, especially when using high-reflectivity braze materials, such as aluminium-based or copper-based alloys. The energy must be distributed adequately by applying beam oscillation transversal to the brazing direction. In laser brazing processes, the temperature field in the interface between brazing and substrate material is a major factor. To analyse the effect of beam oscillation, it is assumed in this study that the temperature distribution at the surface of the melt pool is a suitable approximation for the temperature distribution at the interface to the substrate. Two key parameters are defined to quantify the temperature field referring to the homogeneity: the temporal local temperature-time curve and the temperature distribution transverse to the brazing direction. While the oscillation frequency influences the first mentioned parameter by decreasing the time interval between the local laser passes, the oscillation pattern affects the second parameter by adjusting the local actual beam velocity and its consistency. [ABSTRACT FROM AUTHOR]

Laser brazing is used in automotive production for the joining of car body parts with customer-visible seams, whereby the highest optical seam quality is demanded. During the wetting process, a constriction formation can occur within the molten brazing material, which subsequently collapses; this induces a stepwise progression of the wetting front, thereby decreasing the optical seam quality. The aim of this study is to investigate the influence of the wire and process velocities on this constriction formation. For this purpose, high-speed recordings of the process zone are performed during laser brazing and then evaluated concerning the wetting process. The results show that the constriction formation depends on the relationship between the process velocity and the process direction component of the wire velocity. The constriction formation only occurs when the process velocity exceeds the parallel-oriented component of the wire velocity. This constriction formation is unstable and collapses repeatedly. In this study, increasing velocity differences stabilizes the constriction existence. This stabilization correlates with a uniform wetting process and a reduced frequency of the occurrence of blowout events, probably due to improved outgassing of zinc bubbles from the melt pool. [ABSTRACT FROM AUTHOR]

In this study, the effects of a longitudinal filler wire oscillation on the wetting process in laser brazing are analyzed. High-speed recordings are carried out, and the seams are characterized by light-microscopy analysis with respect to the quality of the seam edges. It is shown that the filler wire oscillation is capable of influencing both the frequency and the amplitude of the wetting front movement. In contrast to the process without filler wire oscillation, which is accompanied by repetitive but irregular collapses of the wetting fronts, the longitudinal filler wire oscillation prevents such collapses and thus increases the seam edge quality. [ABSTRACT FROM AUTHOR]

Laser brazing of zinc coated steel is a well-established joining technology in the automotive industry. So far, only a few studies examined the influence of the processing parameters on the strength of these joints. Thus, the influence of different laser power adjustments on the joints' properties is investigated. The joints are examined by the visual surface inspection, the analysis of micro-sections, quasi static tensile strength tests and dynamic bending tests. Additionally, the influence of the type of zinc coating is investigated for electrogalvanized (EG) and zinc-aluminum-magnesium (ZM) coated steel. At comparatively high laser power adjustments joints manufactured with EG coatings excel the performance of those made with ZM as joints with EG endure up to 94 % more load cycles than joints with ZM during dynamic tests. [ABSTRACT FROM AUTHOR]

Copyright of Laser Technology is the property of Gai Kan Bian Wei Hui and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The wetting behavior in laser brazing can be designated as inconstant, caused largely by external process discontinuities such as the wire feeding. To reveal periodic melt pool propagation effects that occur during laser brazing of aluminum and for a better understanding of those effects in laser brazing in general, this paper analyzes high-speed recordings of the brazing process with aluminum alloy. It is demonstrated that two main effects of periodic melt pool behavior in different frequency scales occur during the process, related directly to the wire feeding. [ABSTRACT FROM AUTHOR]

Automobile laser brazing remains a complex process whose results are affected by several process variables that may result in nonacceptable welds. A multisensory customized inspection system is proposed, with two distinct non-destructive techniques: the potential drop method and eddy current testing. New probes were designed, simulated, produced, and experimentally validated in automobile’s laser-brazed weld beads with artificially introduced defects. The numerical simulations allowed the development of a new four-point probe configuration in a non-conventional orthogonal shape demonstrating a superior performance in both simulation and experimental validation. The dedicated inspection system allowed the detection of porosities, cracks, and lack of bonding defects, demonstrating the redundancy and complementarity these two techniques provide.

In car body manufacturing, the joints in the outer skin exterior shell are especially challenging. They have to fulfill very high surface quality requirements. Laser beam brazing of electrogalvanized steel is a well established process for these joints in the direct view of the customer. However, the quality of the brazed seam is very sensitive to changes in the process parameters or in the environmental conditions. Currently, the process speed is limited due to quality requirements of the brazed seam. In this paper, the authors describe the influence of the brazing speed on the resulting braze seam. By the use of high-speed videography, the authors study the process and analyze the occurring macroscopic effects. The two main effects that can be observed with high-speed videography are surface instabilities and an inhomogeneous movement of the melt pool front. Moreover, the authors could detect a correlation between the movement of the melt pool front and the formation of notches. [ABSTRACT FROM AUTHOR]

Abstract Joints properties of high temperature thermoelectric (TE) modules, which are composed of n-type Mg 2 Si and p-type higher manganese silicide (HMS), were investigated using the laser brazing process. In this process, the direct-bonded copper (DBC) and the TE materials were bonded using the Ag Cu based brazing filler metal. Heating and cooling rates were controlled by changing laser power and irradiation time gradually for preventing from thermal shock damage. The properties of joints were investigated by die shear test and microstructural analysis. As a result, improved joints of TE modules were fabricated through the laser brazing. Suitable heat input condition was deducted to optimize inter-diffusion between the filler metal and TE materials for obtaining reliable bond strength. In order to evaluate the high temperature stability, heat treatments were performed with TE modules using the furnace. As the heat treatment time increased, voids was formed at the joint but the diffusion distance of Cu and Ag did not increase. Highlights • Laser brazing was used to prevent damage to TE materials caused by thermal shock. • Heat input was controlled to optimize inter-diffusion of filler metal and TE materials. • The bond strength was affected by the degree of inter-diffusion. [ABSTRACT FROM AUTHOR]

Abstract Ti activated 72Ag-28Cu filler alloy was reinforced with micro/nano-Al 2 O 3 ceramic particles for active brazing of synthetic diamond grits with 1045 steel. Microstructural changes due to reinforcement and corresponding influence on abrasion resistance characteristics of the modified filler alloy were observed. Different weight percentages (wt%), each of micro and nano-Al 2 O 3 reinforcements, were tried. Micro-Al 2 O 3 ceramic reinforcements were found to be uniformly distributed in the microstructure of the modified filler material. Alumina particles reacted with titanium to form hard Cu 3 Ti 3 O and TiO reaction compounds. Nano-Al 2 O 3 reinforcements showed a tendency to get clustered, impairing the improvement in abrasion resistance property of the primary filler alloy. 1 wt% micro-Al 2 O 3 added filler alloy underwent 58% less volumetric wear than the primary Ag-Cu-Ti alloy during the pin-on-disc test. This micro- reinforced filler also could effectively braze diamond grits with the steel without any significant deterioration in its wetting ability on diamond surface and joint strength, compared to its counterpart having the primary formulation. [ABSTRACT FROM AUTHOR]

Graphical abstract Abstract Ultrasonic vibration (USV) can optimize the microstructure of the seam and enhance the mechanical properties of the joint; thus, it has been employed to profitably assist Al/steel welding–brazing. The effects of USV on Al/steel welding–brazing joining were investigated. Without the USV treatment, coarse aluminum dendrites, the second phases of Al–Si eutectic and Al 3 FeSi with large sizes were formed in the joint. Under the USV treatment, the refinement of the aluminum matrix, spheroidization of the Al–Si eutectic, and fragmentation of Al 3 FeSi were produced, which resulted from the effects of cavitation and acoustic streaming induced by the USV treatment. The maximum value of the tensile shear strength of the ultrasonic–treated joint could be achieved at an optimum ultrasonic vibration power of 0.8 kW, which had ∼30% increment compared with the raw joint, owing to the fine–grained strengthening and dispersing strengthening of Al–Si eutectic and Al 3 FeSi. The ductile fracture was located in aluminum base metal. [ABSTRACT FROM AUTHOR]

Abstract Laser brazing of aluminum 6082 to galvanized steel was carried out with different laser power followed by mechanical and microstructural characterization. Hardness, tensile and low cycle fatigue tests were conducted for mechanical property evaluation, while microstructural analyses were consisted of optical microscopy, SEM and XRD studies. Microstructures revealed the presence of different eutectics at the inter-dendritic region, whereas, ternary Al-Fe-Si and binary iron-rich intermetallics were at the steel interface. Asymmetrical hardness profile throughout the braze joint with lowest value in the brazed region was noted. The sample, brazed with 4 kW laser power, showed best tensile strength, and failed through the base material. Low cycle fatigue tests showed cyclic stabilization at lower strain amplitudes. Fatigue failure occurred in the brazed region and exhibited fatigue striations, flow lines and intergranular cracking. [ABSTRACT FROM AUTHOR]

Dissimilar lap joining of magnesium alloy to titanium alloy was performed using Ni coating by laser welding-brazing process. The influence of different Ni-coating thicknesses on microstructure and mechanical properties were investigated. In laser irradiation region, Ti 3 Al phase formed at fusion zone/Ti interface. In middle region, Ti 3 Al phase still existed at fusion zone/Ti interface, while Mg-Al-Ni ternary IMC generated at fusion zone. In weld toe region, Ti-Ni binary IMC were observed at the interface of fusion zone/Ti. The particles of Mg-Al-Ni ternary compound grew bigger and thickness of Ti-Ni compound layer increased with the increase of Ni-coating thickness. TiNi IMC transformed into (TiNi + Ti 2 Ni) mixtures when the Ni-coating thickness exceeded 5.8 μm. Interfacial microstructure evolution was clarified according to thermodynamic calculation results of formation enthalpy and chemical potential. The fracture load first increased and then decreased slightly with increasing coating thickness, the maximum fracture load (2430 N/cm) represented 90% joint efficiency in relation to the Mg base metal. The fracture mode changed from interfacial failure into fusion zone fracture when the Ni-coating thickness was greater than 4.0 μm. The interfacial bonding were relatively low, while the performance of fusion zone fracture was relatively high. Further increase of coating thickness has little effect on the performance deterioration. The bonding mechanism of Mg to Ni-coated Ti were illuminated. [ABSTRACT FROM AUTHOR]

Dissimilar metal joining between Al and Cu is effective to reduce the cost and weight of electrical components. In this study, dissimilar laser lap brazing of Al containing Ni to pure Cu was conducted, and the effect of the addition of Ni on the joint strength and microstructure at the dissimilar interface was examined. The addition of Ni higher than 2.8 at. pct improved the joint strength effectively, even though the thickness of the IMC layer at the dissimilar interface increased. The addition of Ni additionally produced not only (Ni,Cu)Al particles in θ-Al2Cu but also a (Ni,Cu)Al layer at the θ-Al2Cu/γ1-Al4Cu9 interface. This study implied that the addition of Ni to Al resulted in the formation of a (Ni,Cu)Al layer at the weakest interface between θ-Al2Cu and γ1-Al4Cu9, drastically increasing the strength of the Al/Cu dissimilar joint. [ABSTRACT FROM AUTHOR]

Weld-joint has been atracting attention to assemble structures of dissimilar metals, particularly in automobile industry. However, the application of weld-joint to steel and aluminum plates is still limited due to uncertainty of the fatigue strength. Fatigue strength of weld-joint is rather complicated to evaluate because both effects of stress concentration at the edge and formation of intermetallic compounds along the interface should be considered carefully. This study focused on finding the key factor that determines the fatigue strength of steel-aluminum brazing joint by considering the variation of strength along interface. The welded part of single lap joint was partially removed by a wire-cut electric discharge machine to investigate the influence of length and location of interface on fatigue strength. When the applied load was relatively low it was found that the numbers of cycles to failure were found to be similar, even though the lengths of interface were different due to partial removal. Furthermore, observation on the fracture surface indicated that early stage of crack propagation showed similar topography regardless of the partial removal of weld part. These results clarified that the number of cycles to failure was mainly consumed at the early stage. Finite element analysis was then conducted to investigate the stress component affecting the fatigue strength. As a result, principal stresses were maximum at the fracture initiation site in all the specimens. Therefore, we concluded that fatigue life of weld-joint is dominant in the early stage of crack propagation, which is characterized by the principal stress.

Abstract Dissimilar AZ31B-Mg and Ni-coated Q235A-steel alloys were joined in a lap configuration using a laser welding-brazing process. The effects of the Ni coating thickness on the joint appearance, interfacial reactions and mechanical properties were investigated with the assistance of thermodynamic calculations. In the direct irradiation region, Ni atoms diffused and were accumulated near the interface due to the driving force of the chemical potential. Al atoms from the filler were attracted by the concentrated Ni atoms, which resulted in the formation of the FeAl phase. In the middle region and weld toe region, a Fe(Ni) solid solution formed at the interface. Heterogeneous reaction products were produced at the seam near the interface, varying from only the AlNi phase to the AlNi+(α-Mg+Mg 2 Ni) eutectic with the increase of the coating thickness. Additionally, a bulky Mg 2 Ni phase also formed in the matrix of Mg-Ni eutectic with a coating thickness of 40 μm. Strong mutual attraction occurred between the Al and Ni atoms at the seam, resulting in a higher driving force for generating the AlNi phase than for generating the Mg-Ni phase. All joints were finally fractured at the seam. The maximum value of the tensile-shear fracture load approached 230 N/mm with a Ni coating thickness of 20 μm, reaching an 88.5% joint efficiency relative to the Mg base metal. Highlights • Join Mg and varied-thickness-Ni-coated steel using laser welding-brazing process. • Ni coating significantly influenced the interfacial reaction products. • Thermodynamics calculation explained the interfacial evolution behavior. • The optimum fracture load was obtained with appropriate thickness of Ni coating. [ABSTRACT FROM AUTHOR]

Laser brazing (LB) provides a promising way to join the galvanized steel in automotive industry for its significant advantages including high speed, small heat-affected zone, and high welding seam quality. The process parameters of LB have significant effects on the bead profile and hence the quality of joint. Since the relationships between the process parameters and bead profile cannot be expressed explicitly, it is impractical to determine the optimal process parameters intuitively. This paper proposes an optimization methodology by combining genetic algorithm (GA) and ensemble of metamodels (EMs) to address the process parameters optimization of the bead profile in LB with crimping butt. Firstly, Taguchi experimental design is adopted to generate the experimental points. Secondly, the relationships between process parameters (i.e., welding speed, wire feed rate, gap) and the bead geometries are fitted using EMs based on the experimental data. The comparative results show that the EMs can take advantage of the prediction ability of each stand-alone metamodel and thus decrease the risk of adopting inappropriate metamodels. Then, the GA is used to facilitate design space exploration and global optimum search. Besides, the main effects and contribution rates of multiple process parameters on bead profile are analyzed. Eventually, the verification experiments are carried out to demonstrate the effectiveness and reliability of the obtained optimal parameters. Overall, the proposed hybrid approach, GA-EMs, exhibits great capability of guiding the actual LB processing and improving welding quality. [ABSTRACT FROM AUTHOR]

The laser brazing process is successfully applied in automotive industry for joining of roofs and hatchbacks of vehicles. The bad wetting of the brazing alloy during the process can lead to the formation of random external porosities which are not allowed on visible parts. This paper describes the wettability and reactivity mechanisms at short contact time of Cu and Al matrix brazing alloys with different reactive elements (Si, Sn) on different steel products such as hot-dip galvanized steels, galvannealed steel and bare steel. Wetting experiments were carried out by the dispensed drop technique. The effects of alloying elements and brazing alloy matrix on interfacial reactivity are discussed. It was found that Cu matrix containing 3 wt.% Si is the most favorable for short time liquid/solid adhesion relatively to the other studied brazing alloy compositions. The brazing ability of different steel products is well correlated with the wettability and interfacial reactivity results. [ABSTRACT FROM AUTHOR]

Laser brazing of Al to brass in lap configuration with Zn-based filler was performed in this work. The process parameters including laser power, defocused distance were found to have a significant influence on appearance, microstructure and mechanical properties. The process parameters were optimized to be laser power of 2700 W and defocusing distance of + 40 mm from brass surface. In addition, preheating exerted great influence on wetting and spreading ability of Zn filler on brass surface. The microstructure observation showed the thickness of reaction layer (CuZn phase) at the interface of the brass side would grow with the increase in laser power and the decrease in the laser defocusing distance. Moreover, preheating could increase the spreading area of the filler metal and induced the growth of the reaction layer. The highest tensile-shear load of the joint could reach 2100 N, which was 80% of that of Al alloy base metal. All the joints fractured along the CuZn reaction layer and brass interface. The fracture morphology displayed the characteristics of the cleavage fracture when without preheating before welding, while it displayed the characteristics of the quasi-cleavage fracture with preheating before welding. [ABSTRACT FROM AUTHOR]

Two pieces of plate glass were brazed into a composite of glazing with a vacuum chamber using PbO-TiO 2 -SiO 2 -R x O y powder filler alloys to develop a new type of vacuum glazing. The brazing process was carried out by laser technology. The interface characteristics of laser brazed joints formed between plate glass and solder were investigated using optical microscope, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) techniques. The results show that the inter-diffusion of Pb/Ti/Si/O elements from the sealing solder toward the glass and O/Al/Si elements from the glass toward the solder, resulting in a reaction layer in the brazed joints. The microstructure phases of PbTiO 3 , AlSiO, SiO 2 and PbO in the glass/solder interface were confirmed by XRD analysis. The joining of the sealing solder to the glass was realized by the reaction products like fibrous structures on interface, where the wetting layer can help improve the bonding performance and strength between the sealing solder and the plate glass during the laser brazing process. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate the successful brazing and superior mechanical performance of laser brazed Inconel® 718 using a Ni-Mn-Fe-Co-Cu high entropy alloy filler metal with a nominal Ni:Cu:Co:Fe:Mn molar ratio of 1:1:1:0.25:1.75. A maximum 220 MPa shear strength is achieved. The high entropy alloy experiences the hardness increases 3–4 times after brazing. If the brazing temperature is higher than 1200 °C, the bonding strength suffers due to excessivediffusion between the base metal and the filler metal. The hardness behavior is attributed to a combination of the cocktail effect and lattice distortion induced by brazing. [ABSTRACT FROM AUTHOR]

Real-time monitoring of laser welding plays a very important role in the modern automated production and online defects diagnosis is necessary to be implemented. In this study, the status of laser brazing was monitored in real time using an infrared photoelectric sensor. Four kinds of braze seams (including healthy weld, unfilled weld, hole weld and rough surface weld) along with corresponding near-infrared signals were obtained. Further, a new method called Empirical Mode Decomposition (EMD) was proposed to analyze the near-infrared signals. The results showed that the EMD method had a good performance in eliminating the noise on the near-infrared signals. And then, the correlation coefficient was developed for selecting the Intrinsic Mode Function (IMF) more sensitive to the weld defects. A more accurate signal was reconstructed with the selected IMF components. Simultaneously, the spectrum of selected IMF components was solved using fast Fourier transform, and the frequency characteristics were clearly revealed. The frequency energy of different frequency bands was computed to diagnose the defects. There was a significant difference in four types of weld defects. This approach has been proved to be an effective and efficient method for monitoring laser brazing defects. [ABSTRACT FROM AUTHOR]

Laser welding-brazing process was developed for joining 5052 aluminum alloy and H62 brass in butt configuration with Zn-15%Al filler. Effect of welding speed on microstructural characteristics and mechanical properties of joints were investigated. Acceptable joints without obvious defect were obtained with the welding speed of 0.5–0.6 m/min, while lower and higher welding speed caused excessive back reinforcement and cracking, respectively. Three reaction layers were observed at welding speed of 0.3 m/min, which were Al 4.2 Cu 3.2 Zn 0.7 (τ′)/Al 4 Cu 9 /CuZn from weld seam side to brass side; while at welding speed of 0.4–0.6 m/min, two layers Al 4.2 Cu 3.2 Zn 0.7 and CuZn formed. The thickness of interfacial reaction layers increased with the decrease of welding speed, but varied little at different interfacial positions from top to bottom in one joint. Tensile test results indicated that the maximum joint tensile strength of 128 MPa was obtained at 0.5 m/min, which was 55.7% of that of Al base metal. All the joints fractured along the weld seam/brass interface. Some differences were found regarding fracture locations with three and two reaction layers. The joint fractured between Al 4 Cu 9 and τ′ IMC layer when the interface had three layers, while the crack occurred between CuZn and τ′ phase in the case of two layers. [ABSTRACT FROM AUTHOR]

In this investigation, the joining of two types of galvanized steel and Al6022 aluminum alloy in a coach peel configuration was carried out using a laser welding-brazing process in dual-beam mode. The feasibility of this method to obtain a sound and uniform brazed bead with high surface quality at a high welding speed was investigated by employing AlSi12 as a consumable material. The effects of alloying elements on the thickness of intermetallic compound (IMC) produced at the interface of steel and aluminum, surface roughness, edge straightness and the tensile strength of the resultant joint were studied. The comprehensive study was conducted on the microstructure of joints by means of a scanning electron microscopy and EDS. Results showed that a dual-beam laser shape and high scanning speed could control the thickness of IMC as thin as 3 µm and alter the failure location from the steel-brazed interface toward the Al-brazed interface. The numerical simulation of thermal regime was conducted by the Finite Element Method (FEM), and simulation results were validated through comparative experimental data. FEM thermal modeling evidenced that the peak temperatures at the Al-steel interface were around the critical temperature range of 700–900 °C that is required for the highest growth rate of IMC. However, the time duration that the molten pool was placed inside this temperature range was less than 1 s, and this duration was too short for diffusion-control based IMC growth. [ABSTRACT FROM AUTHOR]

In view of the pore defect of vacuum glazing sealing layer, the research on side edge sealing of laser was made. The phase analysis of microstructure on sealing layer was investigated using scanning electron microscope (SEM) and energy spectrum analysis (EDS) to study the formation mechanism of sealing pores. The influence of laser power and welding rate on sealing edge porosity was researched. The results show that the sealing layer has evenly distributed bilayer structure of wetting layer with few pores caused by the residual gases between the solder particles (external) –melting layer with a large number of mutually disconnected isolated pores (inside). As the increase of laser power, the interface layer is compact and smooth and the pores decline in numbers. When the power exceeds a certain value, the interface becomes unsmooth with the increasing number of pores. The phenomenon of surface defects and blocky structures is generated with lower welding speed and greater energy output. On the other hand, the blocky structures, unmelted solders, pores and cracks are formed by the higher welding speed and smaller energy output. Therefore, the pore defect can be effectively avoided and reduced by the reasonable control of laser power and welding rate. [ABSTRACT FROM AUTHOR]

Wetting steel surfaces with liquid aluminum without the use of flux can be enabled by the presence of a zinc-coating. The mechanisms behind this effect are not yet fully understood. Research results on single aluminum droplets falling on commercial galvanized steel substrates revealed the good wetting capability of zinc coatings independently from the coating type. The final wetting angle and length are apparently linked to the time where zinc is liquefied during its contact with the overheated aluminum melt. This led to the assumption that the interaction is basically a fluid dynamic effect of liquid aluminum getting locally alloyed by zinc. A numerical model was developed to describe the transient behavior of droplet movement and mixing with the liquefied zinc layer to understand the spreading dynamics. The simulations reveal a displacement of the molten zinc after the impact of the droplet, which ultimately leads to an accumulation of zinc in the outer weld toe after solidification. The simulation approach neglects the effect of evaporating zinc, resulting in a slight overestimation of the final droplet width. However, in terms of spreading initiation during the first milliseconds, the simulation is in good correlation with experimental observations and demonstrates the reason for the good wetting in the presence of zinc coatings. [ABSTRACT FROM AUTHOR]