Brazing Sheet Research Articles

Effect of pre-strain on the brazing characteristics of a high-strength aluminum brazing sheet with a barrier layer

Effect of pre-strain on the brazing characteristics of a high-strength aluminum brazing sheet with a barrier layer

Corrosion behavior and mechanism of 4004/Al-Mn-Cu-Mg-Si/4004 aluminum brazing sheet in sea water acidified accelerated test

The microstructure and corrosion properties of a novel 4004/Al-Mn-Cu-Mg-Si/4004 aluminum brazing sheet were investigated in comparison with the traditional 4004/3003/4004. It revealed that, the microstructure after brazing of two aluminum brazing sheets from outer to center were both residual Al-Si eutectic, precipitate-free zone (PFZ), band of dense precipitates (BDP) and core material, respectively. However, the alloying element distribution and the types and amounts of second phases were quite different. The sea water acidified accelerated test showed that 4004/Al-Mn-Cu-Mg-Si/4004 exhibited typical exfoliation corrosion, while the corrosion quickly spread deep into the core material of 4004/3003/4004. The formation of Cu concentration gradient and the strip distribution of Al-Mg-Cu-Si precipitates in the BDP region contributed to the exfoliation corrosion of 4004/Al-Mn-Cu-Mg-Si/4004. The corrosion behaviors of Al-Mn-Cu-Mg-Si and AA3003 core materials are both in form of intergranular corrosion (IGC)，and the later was more severe than the former. For Al-Mn-Cu-Mg-Si core material, high-density fine dispersed cathodic α-Al(Mn, Cu)Si precipitates promoted the formation of a profusion of micro-galvanic cells in the Al matrix, which would retard any effects between the grain boundary precipitations and the adjacent relatively PFZs. Hence, the IGC susceptibility of Al-Mn-Cu-Mg-Si core material was decreased. Besides, less large-sized α-AlFeMn(Cu)Si phases in core material also reduced the localized corrosion attack. At last, the corrosion in depth direction of 4004/Al-Mn-Cu-Mg-Si/4004 was retarded, compared to its counterpart.

The Effect of Microstructural Evolution on the Brazeability of Two-Layer Al Sheets

In this study, the microstructural evolution and the interaction between the clad and the core alloys that occurs during the brazing process of two-layer Al sheets with equiaxed grains were examined. The study was carried out using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD) and glow discharge optical emission spectrometry (GDOES). The effects of microstructure on the brazing performances of two-layer sheets were clarified. Although the grains were fine and equiaxed before brazing, three typical microstructural evolutions happened during brazing, corresponding to three kinds of interactions between the clad and core alloys of the aluminum brazing sheets. In the alloys, which had either relatively uniform grain growth or no grain growth, the interaction between the clad alloy and the core alloy was weak; accordingly, they showed a smooth surface, an even microstructure, faint element mutual diffusion, and eventually good brazeability. Meanwhile, in the alloy with obvious abnormal grain growth (AGG), strain-induced liquid-film migration (SILFM) occurred when the energy was too low to cause strain-induced boundary migration (SIBM). This led to rough and uneven surface morphology, significant mutual diffusion, and surface segregation of elements; eventually, this produced the worst brazeability.

Corrosion Properties for Roll-Bonded Two-Layer AA4045/AA3003 for Heat Exchanger Application

During their service life, heat-exchangers are subjected to a variety of environments, including heating and cooling cycles, salt water environment on the surface, and mechanical loading. As a result, corrosion performance is critical, as perforation of the material could result in system failure. Corrosion behaviour of brazed roll-bonded aluminium sheet is significant since this is the most common mode of failure for automotive heat exchangers, especially with the trend toward lighter automotive parts. Furthermore, thermal treatments such as solution heat treatment, homogenization, and brazing alter the microstructure and, as a result, vary the corrosion behaviour. The effect of homogenization temperature and duration on the microstructure of AA-3xxx aluminium alloys has been studied, but more research is needed. The goal of this investigation was to see how different holding times during homogenization heat treatments affect corrosion behaviour. Accelerated laboratory corrosion tests are essential for ranking trial materials and ultimately qualifying an alloy for production. The corrosion behaviour of two-layer modified aluminium sheets (AA4045/3003 Modified) was examined in this research before and after brazing. The corrosion propagation was attributed to potential differences between the brazing sheet, creating a galvanically driven perforation of the core material by the diffusion zone after sea water acid accelerated testing (SWAAT) and electrochemical testing of the AA4045/3003 modified brazing sheet. Furthermore, a link between SWAAT and potentiodynamic polarization measurements has been established, suggesting that these electrochemical approaches could be used to replace or reinforce the SWAAT and so reduce the cost.

Effect of brazing parameters on fillet size and microstructure of cladded fin-microchannel tube joints

Abstract This work concerns the optimization of furnace brazing conditions for joining micro-multiport aluminum tubes and fins made with AA4343/AA3003/AA4343 brazing sheet in mini-assemblies mimicking the core of an automotive heat exchanger. Taguchi method was used for design of experiment, considering five process parameters with two levels of values. The aim was to maximize the fillet size of the brazed joints, which has an important influence on the thermal integrity and mechanical properties. Fillet length measurements of brazed joints were performed with a metallographic microscope. The statistical analysis allowed to obtain the optimum values of process parameters (peak temperature, residence time, heating rate, microchannel tube type and flux). At a 95% confidence level, the variability of fillet length is most significantly affected by the peak brazing temperature (77%), residence time (15%) and heating rate (7%). The predicted maximum fillet length was (152±11) µm, which was corroborated by confirmation trials. The microstructural analysis of tube−fin joints showed that variations in peak temperature and residence time affect only the size of the eutectic zone of fillet formed, but not the nature or composition of the constituent phases.

Study on the influence of the brazing sheet placement angle on the rotation strength of composite grinding wheel

• The rotation stress formula of the composite grinding wheel is deduced and analyzed. • Cutting off effect of the brazing sheet in the composite grinding wheel is analyzed. • The finite element simulation analysis was used for the wheel rotation performance. • Carried out the grinding wheel rotation test to verify the correctness of the study. A high performance composite grinding wheel with brazed diamond sheets was developed for rail grinding. The rotation stress formula of the composite grinding wheel is deduced and analyzed, and the cutting off effect of the brazing sheet on the resin in the composite grinding wheel is analyzed. The finite element simulation analysis of the rotation performance of the composite grinding wheel is carried out when the brazing sheet is in the middle of the grinding wheel or one end of the brazing sheet is flush with the grinding end of the grinding wheel. The corresponding composite grinding wheel is made to carry on the rotation test, which is compared with the simulation analysis results. The results show that for the Ø260-size rail grinding composite grinding wheel, when using 15 mm wide and 55 mm long brazing sheets, the optimal placement angle is 55°, followed by 60° and 45°. The analysis of the noise detection results of the rotary testing machine shows that the resonance speed of the rail grinding wheel is between 4600–4800 rpm, and the rotary noise of the composite grinding wheel with brazing sheet is lower than that of the resin grinding wheel.

Effect of Cu and Mg on the corrosion behavior of 4004/Al-Mn-Cu-Mg-Si/4004 aluminum alloy brazing sheet

Higher strength and better corrosion resistance are necessary to enable the thickness reduction of the aluminum alloy brazing sheets. In this work, an age-hardenable Al-Mn-Cu-Mg-Si core alloy was developed by the addition of Mg, Si and Cu. The corrosion behavior of 4004/Al-Mn-Cu-Mg-Si/4004 aluminum alloy brazing sheet in sea water acidified accelerated test (SWAAT) was investigated and compared with the traditional 4004/3003/4004 aluminum alloy brazing sheet. The microstructure was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). After brazing, it was found that the microstructures of two aluminum alloy brazing sheets from outer to the center were precipitate-free zone (PFZ), the band of dense precipitates (BDP) and core material, respectively. In particular, both Cu and Mg concentration gradients were formed in the BDP region of 4004/Al-Mn-Cu-Mg-Si/4004. Moreover, the SWAAT results showed exfoliation corrosion in 4004/Al-Mn-Cu-Mg-Si/4004, while in 4004/3003/4004, severe inter-granular corrosion in core material was observed after corrosion for 584 h. The theoretical electric potential distribution showed that the presence of Cu and Mg concentration gradient promoted the formation of the electric potential trough in the BDP region, which may be the reason for the occurrence of exfoliation corrosion in 4004/Al-Mn-Cu-Mg-Si/4004.

Wear characteristics of brazed diamond sheets with different grinding time

In order to expand the application field of tools containing brazed superabrasives, the wear characteristics of brazed diamond sheets, which used in rail-grinding composite grinding wheels, under different grinding time were studied. The brazing sheet’s grinding ratio decreases with time while wear and thermal damage of the diamond abrasive increase. With continuous long-term grinding, the solder shows melt-slip phenomenon, which increases grinding portion of the brazing sheet. Meanwhile, there was partial oxidation of the solder in the wear debris. When the total grinding time is the same, in short-time multiple grinding, the brazing sheet suffers less, higher grinding ratio; the thermal damage of the diamond abrasive is lower and the wear of abrasive is mainly impact crushing, flattening and mechanical shedding.

Dynamic analysis of electromagnetic compaction of Ag-Cu-Sn multivariate mixed metal powders for brazing

Electromagnetic compaction is a preferable high energy rate forming process for brazing powders to improve the brazing performance. The dynamic analysis of electromagnetic compaction of Ag-Cu-Sn multivariate mixed metal powders was conducted by an electromagnetic-mechanical-thermal coupled model an d electromagnetic compaction tests. The coupled model consists of electrical circuit model, electromagnetic field model, kinematic model of driving board, thermal field model and powder compaction model, it can be used to make a complete dynamic analysis of the electromagnetic compaction including discharge current, eddy current, mutual interactions of magnetic fields, kinematic motion of driving board, compaction densification behaviors and the energy transfer. The electromagnetic compaction tests of Ag-Cu-Sn multivariate mixed metal powders were carried out with a self-developed WG-IV electromagnetic forming machine. The electromagnetic-mechanical-thermal coupled model has good agreement with the electromagnetic compaction tests, and can provide a more accurate dynamic analysis and optimized process design of electromagnetic compaction. An optimization study for higher relative density was completed by the coupled model, and the brazing performance of the optimized brazing sheet with higher relative density was evaluated to be advantageous in the brazing performance tests.

Change in porous structure and liquid phase migration in bonding porous aluminum with an Al–Si based alloy brazing sheet

Change in porous structure and liquid phase migration in bonding porous aluminum with an Al–Si based alloy brazing sheet

Study on wear characteristics of brazed diamond sheet for rail’s composite grinding wheel under different pressures

To improve the performance of grinding wheels for rail, a composite grinding wheel was developed by combining brazed diamond sheets and original resin grinding wheel. An experimental methodology for grinding process was established to study the grinding wear characteristics of the brazed sheet. The results indicate that with increasing working load, the wear rate of the brazing sheet increases and the grinding ratio decreases. In addition, the temperature rise becomes faster and the proportion of oxidation products in the grinding debris increases. Brazing alloy shows melt-slip phenomenon when grinding was performed continuously for a long time. When the worn brazing material is mixed with iron debris, the mixture hinders agglomeration and shrinkage of the molten debris.

Effect of Warm Forming on Formability and Springback of Aluminum Alloy Brazing Sheet

This paper investigates the effect of warm forming (up to 350°C) on the formability and springback behavior of AA3003/AA4045 brazing sheet (0.2 mm gauge) for two temper conditions: O- and H24-temper. The key objective is to utilize warm forming to form aggressive geometries and control the springback to improve the part flatness which enables the use of harder temper material with improved strength. Simulations and experiments are performed considering heated dies at several different temperatures up to 350 °C and the blanks are pre-heated in the dies. The geometry under study is referred as a surrogate heat-exchanger component (SHC) and contains complex features found on commercial automotive thermal management systems. An in-depth springback characterization was completed for a wide range of forming process parameters such as: temperature, punch load, sheet direction, and holding time. Numerical simulations were also performed to predict the springback behavior and were compared to the experiments. There were no clear results showing improvement in formability using the warm forming process. However, increased temperatures (above 250 °C) offered significant improvement in springback for the harder H24 material temper.

Liquid–Solid Interaction in Al-Si/Al-Mn-Cu-Mg Brazing Sheets and Its Effects on Mechanical Properties

The liquid–solid interaction during brazing at 592 °C to 605 °C and its effects on mechanical properties were investigated in a series of Al-Si/Al-Mn-Cu-Mg brazing sheets with different Mg contents. Depending on the Mg level in core alloy and the brazing temperature, critical changes of local chemistry and microstructure related to the liquid–solid interaction occur, including solid-state diffusion, uniform clad–core interface migration, and grain boundary penetration (GBP). When the Mg in core alloy is below 1 wt pct, the interaction is limited and the formation of a dense precipitation band due to solid-state diffusion of Si from the clad to the core is dominant. As the Mg exceeds 1 wt pct, very extensive interaction occurs resulting in clad–core interface migration and GBP of Si into the core, both involving local melting and re-solidification of the core alloy. Whenever Si from the clad encounters Mg in the core due to the interaction, Mg2Si precipitates are formed leading to significant improvement of strength. However, the interface migration and GBP drastically reduce the ductility, due to the segregation of coarse secondary phase particles along the newly formed grain boundaries.

Surface development of a brazing alloy during heat treatment–a comparison between UHV and APXPS

In an attempt to bridge the pressure gap, APXPS was used to follow the surface development of an aluminum brazing sheet during heating in an ambient oxygen-pressure mimicking the environment of an industrial brazing furnace. The studied aluminum alloy brazing sheet is a composite material consisting of two aluminum alloy standards whose surface is covered with a native aluminum oxide film. To emphasize the necessity of studies of this system in ambient sample environments it is compared to measurements in UHV. Changes in thickness and composition of the surface oxide were followed after heating to 300 °C, 400 °C, and 500 °C. The two sets presented in this paper show that the surface development strongly depends on the environment the sample is heated in.

Sagging resistance of warm formed aluminum brazing sheet

Interrupted tensile tests, performed between room temperature (RT) and 250°C, were used to simulate warm forming of an AA3003/AA4045 brazing sheet. Brazing performance was predicted from sagging distance measurements after a thermal cycle. The sagging distance as a function of strain for sheets strained at 150°C was similar to that of RT strained samples, while the sagging distances were larger at all levels of applied strain for sheets strained at 200°C and 250°C. Large sagging distances were correlated with the occurrence of liquid film migration during simulated brazing and a recovered substructure in the core alloy, while small sagging distances were associated with a coarse, recrystallized core alloy. The poor brazing performance of sheets formed above 150°C was attributed to a reduction in the stored strain energy during forming, resulting in recovery rather than recrystallization during brazing, leaving a microstructure which is susceptible to liquid film migration.

Liquid Film Migration in Warm Formed Aluminum Brazing Sheet

Warm forming has previously proven to be a promising manufacturing route to improve formability of Al brazing sheets used in automotive heat exchanger production; however, the impact of warm forming on subsequent brazing has not previously been studied. In particular, the interaction between liquid clad and solid core alloys during brazing through the process of liquid film migration (LFM) requires further understanding. Al brazing sheet comprised of an AA3003 core and AA4045 clad alloy, supplied in O and H24 tempers, was stretched between 0 and 12 pct strain, at room temperature and 523K (250 °C), to simulate warm forming. Brazeability was predicted through thermal and microstructure analysis. The rate of solid–liquid interactions was quantified using thermal analysis, while microstructure analysis was used to investigate the opposing processes of LFM and core alloy recrystallization during brazing. In general, liquid clad was consumed relatively rapidly and LFM occurred in forming conditions where the core alloy did not recrystallize during brazing. The results showed that warm forming could potentially impair brazeability of O temper sheet by extending the regime over which LFM occurs during brazing. No change in microstructure or thermal data was found for H24 sheet when the forming temperature was increased, and thus warm forming was not predicted to adversely affect the brazing performance of H24 sheet.

Improved Corrosion Resistance of Aluminum Brazing Sheet by a Post-Brazing Heat Treatment

This work studies the influence of the microstructure on the corrosion mechanism and susceptibility of as-brazed aluminum sheet. Various microstructures are obtained using postbrazing heat treatments developed to enhance the corrosion resistance of an AA4xxx/AA3xxx brazing sheet. The heat treatment results in a decrease of the matrix Si content within the heat affected zone and an increase of the Si fraction in the α-Al(Fe-Mn)Si phase. Additionally, the effect of the heat treatment on the local electrochemical activity and corrosion properties are studied. The results indicate that the corrosion susceptibility of the as-brazed structure is diminished resulting from of an amendment of the local electrochemical behavior of the outer clad surface after the post-brazing heat treatment. Moreover, the potential difference between the clad material and core is increased, resulting in an improved sacrificial cathodic protection of the core by the re-solidified clad layer.

The Effect of Anodic Oxide Films on the Nickel-Aluminum Reaction in Aluminum Braze Sheet

The influence of an anodic oxide surface film on the nickel-aluminum reaction at the surface of aluminum brazing sheet has been investigated. Samples were anodized in a barrier-type solution and subsequently sputtered with nickel. Differential scanning calorimetry (DSC) and metallography were used as the main investigative techniques. The thickness of the anodic film was found to control the reaction between the aluminum substrate and nickel coating. Solid-state formation of nickel-aluminum intermetallic phases occurred readily when a relatively thin oxide film (13 to 25 nm) was present, whereas intermetallic formation was suppressed in the presence of thicker oxides (~60 nm). At an intermediate oxide film thickness of ~35 nm, the Al3Ni phase formed shortly after the initiation of melting in the aluminum substrate. Analysis of DSC traces showed that formation of nickel-aluminum intermetallic phases changed the melting characteristics of the aluminum substrate, and that the extent of this change can be used as an indirect measure of the amount of nickel incorporated into the intermetallic phases.

Analysis of aluminium brazing sheet differential scanning calorimetry data

Differential scanning calorimetry (DSC) measurements have provided insight into metallurgical reactions which can occur during joining of Al brazing sheet. Researchers have claimed that DSC is sensitive enough to differentiate between brazing sheets with different initial conditions; however, no rigorous proof of this claim has been given. The sensitivity of DSC measurements, as measured by changes in melting peak area, to experimental factors such as DSC sample preparation, sample orientation during testing and starting sheet temper has been investigated. A 23 factorial design was used, and the results were analysed using analysis of variance. The results showed that only the sheet punching direction during sample preparation had a statistically significant influence on the DSC measurements. Microstructure analysis revealed that punching on the core layer of the sheet led to extra clad alloy on the side of the sample, which melted during heating and contributed to a greater measured melting peak area.

Electrochemical behavior of tube-fin assembly for an aluminum automotive condenser with improved corrosion resistance

An aluminum automotive condenser was designed to exhibit high corrosion resistance in the seawater acetic acid test (SWAAT) combining zinc coated microchannel tubes and fins made with AA4343/AA3003(Zn)/AA4343 brazing sheet. Electrochemical measurements in SWAAT solution were carried out under laboratory conditions using tube-fin assembly and individual fin and tube samples withdrawn from the condenser core. The aim was to gain information on the protective role of the zinc sacrificial layer and about changes in corrosion behavior as a function of immersion time. External corrosion of the tube-fin system was simulated by immersion of mini-core samples under open circuit conditions. The corrosion rate increased rapidly during the first 6h and slowly afterwards. The short time behavior was related to the dissolution of the oxide film and fast dissolution of the outermost part of the zinc diffusion layer. With the aid of cross-sectional depth corrosion potential profiles, it was shown that as the sacrificial layer gets dissolved, the surface concentration of zinc decreases and the potential shifts to less negative values. The results of galvanic coupling of tube and fins in a mini-cell showed that the tube became the anode while the fins exhibited cathodic behavior. An evolution in the galvanic interaction was observed, due to the progressive dissolution of the sacrificial zinc layer. The difference of uncoupled potentials between tube and fins decreased from 71mV to 32mV after 84h of galvanic coupling. At the end of such period there was still a part of the zinc sacrificial layer remaining which would serve for protection of the tube material for even longer periods and there were indications of slight corrosion in the fins.