Strength Of Brazed Joints Research Articles

Optimized design of composition and brazing process for Cu-Ag-Zn-Mn-Ni-Si-B-P alloy brazing material based on machine learning strategy to improve brazing properties

As brazing devices become more sophisticated and service environments become more demanding, Cu-Ag-Zn-Mn-Ni-Si-B-P brazing material are subjected to higher wettability and brazed joint strength requirements. In this paper, a machine learning strategy is proposed. Firstly, the composition-process-properties dataset is obtained based on high-throughput experimental techniques. Then, the composition features are constructed by elemental chemical and physical parameters instead of the direct input of alloy composition, and the proposed novel feature selection method is used to effectively identify the key composition feature combinations that affect brazing properties. Then, the support vector regression algorithm was used to establish a joint strength model with an error of less than 3.47 % and a spreading area model with an error of less than 8.37 % using the key alloy composition features and brazing process features as inputs, respectively. Finally, two multi-objective optimization strategies, Bayesian optimization and NSGA-II genetic algorithm, were used for the integrated optimization design of composition and brazing process. The experimental results show that the Cu-14Ag-4Zn-24Mn-13.5Ni-0.4Si-0.3B-0.3 P alloy and the matched brazing process (945 °C and 12 min) were optimally designed using NSGA-II genetic algorithm, corresponding to the measured joint strength and spread area of 356 MPa and 412 mm2, respectively, which outperforms the high-throughput experimentally optimized data as well as commercialized data. The machine learning strategy established in this work provides a new research idea for the comprehensive improvement of brazing properties of brazing alloys with small data sets.

Mathematical model of short-term static strength of the overlap joint from low carbon steel brazed with tin

ABSTRACT A mathematical model of a brazed joint strength consisting of position and scattering characteristics is introduced. Random and residual errors are taken into account for the scattering characteristics. It is shown that the nature of the error distribution relative to the position characteristics must be considered using untruncated and truncated distribution functions. The lower confidence limit of the destructive stresses of the joint made of steel St3 and brazed with tin is determined, with a confidence coefficient of 0,95 and the upper limit of the stress allowance for a brazed joint with a safety factor of 1,5.

Microstructure and Shear Strength of Brazing High Entropy TiZrHfNbMo Alloy and Si3N4 Ceramics Joints

The effects of different brazing processes on the interfacial microstructure and shear strength of TiZrHfNbMo high-entropy alloy (HEAS) and Si3N4 ceramic brazed joints were studied. There is no obvious defect in a brazed TiZrHfNbMo HEAS/AgCuTi/Si3N4 ceramic joint, and the two materials have good metallurgical bonding. The typical interface microstructure is Si3N4/Ti5Si3/Ag solid solution +Cu (s,s)+ CuTi/Cu2Ti/Cu4Ti + TiCu(Hf,Zr)NbMo/TiZrHfNbMo HEAs. With the increase of brazing temperature, the dispersed CuTi phase agglomerates in the brazed joint, and acts as the nucleate of the Cu-based solid solution. The thickness of the reaction layer increases with the increase of phases in the reaction layer on both sides of the joint. When the brazing temperature is 800 °C, 820 °C, 840 °C and 860 °C, the shear strength of the brazed joint is 30 MPa, 72 MPa, 86 MPa and 21 MPa, respectively. The formation of CuTi and Ti5Si3 intermetallic compounds increases the thickness of the reaction layer, and improves the strength of the joint. However, excessive CuTi and Ti5Si3 intermetallic compounds lead to a significant decrease in joint strength. The grain coarsening of the joint can also affect the strength of the joint.

Al-Si-Zn Behaviouron Interface of AR500 Steel and AA7075 Aluminium Alloy BrazedJoint

The brazing of steel and aluminium alloy using low melting point aluminium based fillers has been extensively studied and the technique has been used in many industries, especially the automotive industry. The strength and failure mode of AR500 steel and AA7075 aluminium alloy brazing joint using the Al-Si-Zn filler metal will be measured and calculated in this paper. However, the adverse effect of intermetallic phases formation on the joint strength has limited the application of this joining method.These dissimilar metals possessing a high strength joint would be of benefit to industry especially in reducing the weight of products. The torch brazing method using Al-Si-Zn base filler metal wasused to join AR500 steel and AA7075 aluminium alloy in this study. The intermetallic phase formation of the brazing on was investigated by scanning electron microscopy and the mechanical strength of the joints was evaluated by shear testing, flexural testing and low velocity impact testing. A maximum shear load of 6460 N was obtained. The presence of intermetallic phases was found to have some effect on the strength of the brazed joint. However, overall, this brazing process using Al-Si-Zn filler metal facilitates the joining of these dissimilar metals to improve the mechanical properties of the joint

Predicting the Structural Reliability of LNG Processing Plate-Fin Heat Exchanger for Energy Conservation

Liquefied natural gas (LNG) is one of the hydrocarbon fuels with the least carbon footprint having a rapidly rising global share in the prime energy market. LNG processing for transportation at longer distances works under cryogenic conditions, especially when used for liquefaction and gasification applications. The supply chain of the eco-environmental friendly hydrocarbon is heavily dependent on the processing plant used for liquefaction and subsequent re-gasification of the natural gas. Plate-fin heat exchangers are extensively used in the LNG industry for both re-gasification as well as liquefaction processes. The exchange of heat during the process of natural gas phase change involves plate-fin heat exchangers working under cryogenic low-temperature conditions. The heat exchangers are designed to have brazed joints that are most vulnerable to failure under these temperature conditions. One failure of such a joint can not only hinder the supply chain but also may result in fire and life hazards. In almost all earlier studies, analytical and numerical methods were used to analyze these braze joints using finite element method methods and examining the stresses while keeping them at or near to ambient conditions. In this research, the plate-fin heat exchanger is investigated for its structural stability of brazed fins for three different fin configurations: plain, wavy and compound having different joint geometries. In addition, the analyses are carried out using experimentally measured brazed joint strength which is measured to be on average 22% lower than the base material strength owing to brazing process and resultant heat-affected zone (HAZ). Therefore, the reliability is assessed for these joints in terms of factor of safety (FOS) while keeping in view the actual yield criteria. It was found that the structural stability of compound fins configuration is weakest amongst all considered fin configurations. The failure of the compound fin brazed joint is expected to be along the horizontal path of the joint due to yielding. The study also predicts the life of the fin brazed joints in different joining directions with different topologies of fins commonly recommended in the literature. It is observed that the commonly recommended safe fin geometries are predicted to be susceptible to failure if a reduction in the brazed joint is considered. The analysis and recommendation in this paper shall provide a reliable and safe design approach for plate-fin exchangers for different operating conditions especially in low to cryogenic temperature applications.

Fast responsive control of current and voltage waveforms for gas metal arc brazing of thin zinc-coated steel sheets

Thin zinc-coated steel sheets are brazed together using a copper-silicon filler alloy and employing a gas metal arc process with dynamic control of current and voltage transients. The actual heat inputs for different wire feed rates during brazing were estimated from the recorded current and voltage transients. Lowering of heat input was aimed at to reduce the thermal distortion and the thickness of the interface layer with intermetallic compounds while ensuring a sound, continuous bead profile. The influence of overall heat input on the thermal distortion, joint strength and interface layer thickness is examined using Fourier number that depicts a ratio of the rate of heat dissipation to accumulation. An increase in brazing speed and a decrease in the wire feed rate resulted in reduced heat input, higher Fourier number, thinner interfacial layer and improved joint strength. The brazing induced thermal distortion reduced with increase in Fourier number. Irrespective of the sheet thickness, a range of Fourier number in between 0.22–0.26 provided brazed joint strength up to 96 % of that of the base metals with minimum interface layer thickness and thermal distortion.

Impact of Tin and Nickel on the Brazing Properties of Silver Filler Metals and on the Strength of Brazed Joints Made of Stainless Steels

Abstract The research involved vacuum tests of brazing properties of silver filler metals, containing tin as well as tin and nickel, and used in brazing of chromium X6Cr17 and chromium-nickel X6CrNiTi18-10 stainless steels. The research also involved testing the strength and structural properties of brazed joints made of these steels. The tests were conducted on filler metals (silver brazing alloys) B-Ag68CuSn-730/755 (Ag68Cu28Sn4) and B-Ag65CuSnNi-740/767 (Ag65Cu28Sn5Ni2) and also, for comparative purposes, on the filler metal B-Ag72Cu-780 (Ag 272 according to PN-EN ISO 17672), most commonly applied in the vacuum brazing of high alloyed stainless steels. The brazing properties of the filler metals were tested by determining their wettability by means of the spreadability method. The strength of brazed joints made of the stainless steels was examined in a shear test. Research-related structural tests involved light and electron microscopy with an energy dispersive spectrometer (EDS). The comparative analysis of the properties of the filler metals revealed the positive impact of tin and nickel on the spreadability and wettability of the silver brazing alloys as well as on the quality and the shear strength of brazed joints.

Increasing Ti–6Al–4V brazed joint strength equal to the base metal by Ti and Zr amorphous filler alloys

Microstructural features developed along with mechanical properties in furnace brazing of Ti–6Al–4V alloy using STEMET 1228 (Ti–26.8Zr–13Ni–13.9Cu, wt.%) and STEMET 1406 (Zr–9.7Ti–12.4Ni–11.2Cu, wt.%) amorphous filler alloys. Brazing temperatures employed were 900–950 °C for the titanium-based filler and 900–990 °C for the zirconium-based filler alloys, respectively. The brazing time durations were 600, 1200 and 1800 s. The brazed joints were evaluated by ultrasonic test, and their microstructures and phase constitutions analyzed by metallography, scanning electron microscopy and X-ray diffraction analysis. Since microstructural evolution across the furnace brazed joints primarily depends on their alloying elements such as Cu, Ni and Zr along the joint. Accordingly, existence of Zr2Cu, Ti2Cu and (Ti,Zr)2Ni intermetallic compounds was identified in the brazed joints. The chemical composition of segregation region in the center of brazed joints was identical to virgin filler alloy content which greatly deteriorated the shear strength of the joints. Adequate brazing time (1800 s) and/or temperature (950 °C for Ti-based and 990 °C for Zr-based) resulted in an acicular Widmanstätten microstructure throughout the entire joint section due to eutectoid reaction. This microstructure increased the shear strength of the brazed joints up to the Ti–6Al–4V tensile strength level. Consequently, Ti–6Al–4V can be furnace brazed by Ti and Zr base foils produced excellent joint strengths.

Fracture Mechanism of Aluminum Joint Brazed by Zn-Al Alloy

Zn-Al alloy microstructures were investigated, moreover, the strength and microstructures of pure aluminium brazed joint had been studied. Joint fracture mechanism was analyzed. The results indicate that the blocky microstructure in the cast 85Zn-15Al filler metal is granular and fine. Accordingly, the blocky eutectoid structure in the joint brazed by 85Zn-15Al is fine and even. Stress concentration emerges difficultly between fine blocky eutectoid structure and its surrounding structure. So the joint strength is highest. When Al content in the Zn-Al alloy exceeds 15wt.%, the blocky eutectoid structure become large in the cast filler metal and the brazed joint. The brazed joint strength decreases.

Microstructure and Properties of Zn-Al Filler Metal Brazing Cu/Al Joint

Microstructure and properties of Zn-xAl alloy were investigated, moreover, the strength and microstructure of the Cu/Al brazed joint had been studied. The results indicate that the massive microstructure is granular and fine when Al content is under 15wt.% in the cast microstructure of Zn-xAl filler metal. Meanwhile, the drawability properties of the filler metal is excellent. Thus, the massive microstructure become dendritic and coarse when Al content exceeds 15wt.%. At the same time, the drawability properties of the filler metal become bad. In the microstructure of the brazed joint, the interface layer exists in the interface between the Cu base metal and the brazed seam. The interface layer is mainly consisted of Cu9Al4 and CuAl IMCs. When Al content is under 15wt.%, the interface layer shape is a visibly serrated edge, so the adhesive strength between the interface layer and the brazed seam is higher and the mechanical property of the brazed joint is excellent. The brazed joint strength of Zn-15Al filler metal get highest. But the interface zone become relatively straight when Al content exceeds 15wt.%. In the meantime, the strength of the brazed joint decreases.

Brazing of A5056 aluminium alloy with the aid of ultrasonic vibration using Ag filler metal

In order to produce a high strength brazed joint of A5056 aluminium alloy containing magnesium of about 5 mass%, the authors applied a flux-free brazing method with the aid of ultrasonic vibration to the aluminium alloy by selecting pure Ag foil as brazing filler metal and examined the effect of brazing conditions on the joint properties. The main results obtained in this study are as follows. At a brazing temperature of 570°C, just above the eutectic point of Al–Ag binary system, application of ultrasonic vibration for 4.0 s provided the brazed joint with the maximum tensile strength and the strength decreased with the application time. When the brazing temperature was varied from 550 to 580°C and the application time of ultrasonic vibration was kept constant at 4.0 s, the joint brazed at 560°C attained the maximum tensile strength and fractured in the base metal. It was found that using a pure Ag foil as brazing filler metal successfully brazed A5056 aluminium alloy and the joint strength was equivalent to that of the base metal. Fracture of the joint was prone to occur along the (Al3Mg2 + Al solid solution) phase with high hardness formed at the grain boundary of the base metal. The amount of the hard (Al3Mg2 + Al solid solution) phase increased with the ultrasonic application time and the brazing temperature. It seemed that the increase of the hard (Al3Mg2 + Al solid solution) phase mainly caused the brazed joint strength to decrease.

純銀によるA5056アルミニウム合金の超音波併用ろう付

In order to produce a high strength brazed joint of A5056 aluminum alloy containing magnesium of about 5 mass %, the authors applied the flux-free brazing method with the aid of ultrasonic vibration to the aluminum alloy by selecting pure Ag foil as brazing filler metal and examined the effect of brazing conditions on the joint properties. The main results obtained in this study are as follows.At the brazing temperature of 570°C just above the eutectic point of Al-Ag binary system, applying of ultrasonic vibration for 4.0s provided the brazed joint with the maximum tensile strength and the strength decreased with the applying time. When the brazing temperature was varied from 550°C to 580°C and the applying time of ultrasonic vibration was kept constant at 4.0s, the joint brazed at 560°C attained the maximum tensile strength and fractured in the base metal. It was found that using a pure Ag foil as brazing filler metal successfully brazed A5056 aluminum alloy and the joint strength was equivalent to that of the base metal. Fracture of the joint was prone to occur along (Al3Mg2+Al-solid solution) phase with high hardness formed at the grain boundary of the base metal. The amount of the hard (Al3Mg2+Al-solid solution) phase increased with the ultrasonic applying time and the brazing temperature. It seemed that the increase of the hard (Al3Mg2+Al-solid solution) phase mainly caused the brazed joint strength to decrease.

Ｇｅ含有アルミニウムろうによるＡｌ‐Ｍｇ，Ａｌ‐Ｍｇ‐Ｓｉ合金のろう付

Vacuum brazing of A5000 (Al-Mg) series and A6000 (Al-Mg-Si) series aluminum alloys are considerably difficult because of their rather high magnesium contents. For the purpose of sound and high strength brazing of these materials, a series of Al-Ge-Si-Mg system based filler metales was developed by the authors. Evaluations of brazed joint strength of A5052 and A6061 base alloys with these filler metals were performed and the relationship between the joint strength and the brazing conditions was investigated.In A6061 base alloy, the brazed joints provided sufficient joint strength which were equal to that of the base alloy. In A5052 alloy, on the other hand, the joint strength was considerably low which was as low as one half of that of the base alloy.The examination of brittle intermetallic compound Mg2Ge through the reaction between Mg in the base alloys and Ge in the filler metals occured at the interfaces of the brazed joints. Accordingly the formation of this intermetallic compound lead the decrease in the joint strength of A5052 alloy, which contains much Mg.

超音波映像法を用いた超硬合金と銅タングステンろう付部の品質評価の研究

This report discussed the new method to evaluate the brazed joint strength between cemented carbide alloy and sintered Cu-W joint by using the ultrasonic image. The brazing was performed in a vacum at 1213 K to 1333 K for 60 s to 1.2 ks to vary the joint strength. Although the joint strength made by filler metal containing Pd closed to that of the base metal, Cu-W, at 1213 K, it decresed at higher temperature heating and after prolonged holding time.The ultrasonic image of the brazed joint was measured through the cemented carbide alloy of 4 mm in thickness. In order to correlate a brightness of the ultrasonic image with the joint strength, the relative echo intensity, R, was defined by equation (1)R=1/16n nΣl=1 I/di/Iri (1)where Iri is reference data, Idi is sampling data and n is sampling number. R calculated from these data correlated to the shear strength. Good correlation with r=-0.86 was achieved between R and the joint strength. A microstructure in the joint cross section was investigated comparing with the ultrasonic image.

ＮｉろうによるＳＵＳ３０４継手強さの特性に関する研究（第２報） クリープ破断強さとろう付間隙がクリープ破断強さに及ぼす影響

ＮｉろうによるＳＵＳ３０４継手強さの特性に関する研究（第２報） クリープ破断強さとろう付間隙がクリープ破断強さに及ぼす影響

ＮｉろうによるＳＵＳ３０４継手強さの特性に関する研究 （第１報）

In this study, the influence of brazing process conditions on the Ni brazed joint (Ni-Cr-B) strength of SUS304 stainless steel has been investigated by the tensile test, microscopy, EPMA and SEM. The effects of the brazing clearance, the brazing temparature, and the holding time at brazing temperature are described. The tensile test results show that the Ni brazed joint strength of SUS304 is found to depend on the brazing clearance and the brazing temperature.The results obtained are as follows ;(1) The brazed joint strength depends on the brazing clearance and its maximum strength is obtained at the brazing clearance of 20μm.(2) In the metallographical analysis, it is observed that considerable amount of Ni rich fragments concentrate at the central line zone of the brazing layer. The mass of Ni element may correspond to the original brazing alloy. At the clearance more than 50 μm, the segregation (B-Cr) can be observed at the central line zone of the brazing layer.(3) The brazed joint strength depends on the brazing temperature and its minimum strength is obtained at the brazing process temperature 1380 K with the brazing temperature holding time of 600 sec. This temperature (1380 K) fosters the segregation (B-Cr) of the brazing alloy and the joint strength is related to its segregation size.

軟鋼のろう付強度におよぼす表面状態の影響(第6報)

According to the researches already carried out, it is clear that brazed joint strength of specimen with coarse brazing surface is greater than that of ones with smooth brazing surface. It is considered that these phenomena depends on the effect of the following factors:1) Actual contact area of brazed joint.2) Residual stress of brazed joint.3) Hardness distribution of brazed joint.This paper presents some experimental evidence of residual stress measured by X-ray stress maesuring process and hardness distribution measured by micro-Vickers hardness tester. To obtain smoe experimental data, 10 × 32 × 2.6/m/m mild steel as the base metal and BAg-8 as a filler metal were prepared, and the abutting surfaces of base metals were Polished with various emery papers (No. 60, 120, 240, 400, 600mesh) to set up various roughnesses on the brazing surface. These specimens were brazed with BAg-8 filler metal in the 35 kW resistance furnace operated in hydrogen atmosphere. Residual stress measuremtnt was carried out by means of an X-ray Rstess measurement diffractometer manufactured by Tokyo Shibaura Electric Co.These examinations gave the results as follows:1) Residual stress of brazed joint with coarse surface was larger than that of ones with smooth brazing surface.2) Eesidual stress of y directio n (Fig. 7, 8) was larger than that of x direction; it is considered that these phenomena were caused by soliditic shrinkage of filler metal at the brazed joint.3) Most of these residual stresses were tension stresses, their max value being 4.5kg/mm2 and their min, value being 0.1kg/mm2.

ろう付の強度(第3報)

In the previous paper the authors had shown that the brazed joint strength depended on the clearance of joint.In this report the authors clarified that the difference in the effect of the joint clearance between tension and bending test was due to the stress distribution in the brazed joint.