Dumping and Recovery of Flux Slurry

Dumping
With continuous use, a flux slurry will eventually become contaminated. So far, there is no data that correlates the level of accumulated contaminants with poor brazing. Therefore, it is better to be on the safe side rather than wait till the number of rejects rise due to a contaminated or dirty slurry. It is therefore recommended that a slurry should be dumped when there is visual evidence of contamination. If there is an oil slick floating on top of the slurry in the reservoir or when it is discolored, the slurry should be dumped and replaced with fresh slurry. Alternatively, to avoid misjudging the quality of slurry visually, the slurry could be dumped at regular intervals, especially if the manufacturer knows that the cleanliness of the heat exchangers entering the fluxing booth is not ideal. Experience will dictate how often the slurry should be dumped.

Note however that some heat exchanger manufacturers almost never dump their flux slurries or if they do it might be only once per year. This is only the case when the heat exchangers are very well degreased prior to entering the fluxing booth and efforts are made to avoid undue contamination of the slurry. Simply keeping the cover closed on the slurry tank reservoir will keep out airborne contaminants and lengthen the slurry life.

What to do with the used flux slurry is treated covered under wastewater.

Flux Recovery – Recycle and reuse?
Around the flux slurry preparation station or around the perimeter of the fluxing booth, there will inevitably be some flux on the floor. The inclination is to sweep up this flux and throw it into the flux slurry reservoir or back into the flux drum. This action should be avoided at all costs. Any flux that falls on the floor should be disposed of promptly. The reason is that there are too many contaminants in a manufacturing environment that can affect brazing or cause other damage. Cigarette butts, paper clips, dust, dirt, oil, paper and so on can all have very damaging effects to the flux delivery system and on the brazed products. If the flux is on the floor, dispose of it and do not reuse it.

Spilled Flux

Flux powder on the plant floor should be collected by vacuum cleaners equipped with high efficiency particulate air (HEPA) filters, dedicated central vacuum systems or a wet vacuum system. Avoid sweeping and the use of compressed air. Small wet spills may be mopped up. To remove large spills the floor should be hosed down with water. Waste and contaminated water must be disposed of in accordance with local regulations.

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Water Quality for Flux Slurry

De-ionized (DI) or reverse osmosis (RO) water is recommended to make up the flux slurries. This is to avoid long-term accumulation of mineral deposits in the flux delivery system that can cause blockage of nozzles and/or inadvertently drop on the heat exchanger. Furthermore, local plant or city water may contain ppm levels of contaminants such as chloride and copper that are detrimental with respect to corrosion performance. Other contaminants may also be present which can affect brazing. Furthermore, to avoid any seasonal variations in water quality, to avoid variations in water quality between manufacturing locations and so on, it is highly recommended that DI or RO water is used to make us flux slurries.

Water analysis recommended

In general, it is difficult to comment on potential effects of trace impurities in the flux slurry water without knowing more details about the character of the contamination. There may be only very little influence on the brazing results even with 1,000 μScm-1 conductivity. However, it is necessary to perform a chemical analysis of the water for further evaluation in each case.

The use of de-ionized water has always been recommended to prevent scale build up in the flux delivery system. Reverse osmosis (RO) water is also used successfully. There are no recommendations on conductivity or maximum hardness values (except those related to the calcium levels as listed below). The only reference Solvay Fluor can provide is the conductivity of the de-ionized water used at our Technical Services and Analytical Department in Hanover, which is below 0.2 μScm-1.

As far as we know, no scientific study was yet conducted to determine water quality requirements for aluminum brazing. In collaboration with Alcan, Solvay Fluor has established guidelines for maximum impurity limits for water quality based on contamination which might interfere with brazing or cause discoloration of the brazed parts:

[table id=3 /]

For Chloride a maximum of 0.02% is specified (corrosion problems). Based on experiences at some customer locations with post braze odor in the past, Sulfates should be below 0.02%. Phosphates can cause problems with post braze odor too, due to the potential formation of PH3. Silicates are known to interfere with flux activity. Borates and Silicates can cause black spots on post braze flux residue.

Residual hydrocarbons on all aluminum surfaces should be limited to the lowest level possible, due to the potential formation of carbonaceous residue and the long term corrosion problems caused by this residue. The same applies to all other carbon containing trace impurities in the system.

Most of the above information refers to flux and flux slurry contamination. However, it also relates to other additives and chemicals in the process, particularly when those additives cannot be,- or are not-, removed from the fluxed component prior to reaching brazing temperature.

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Paint Fluxing – Pros and Cons, Part 2

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Selective Pre-Fluxing with Adhesives – Fashion or Progress

Summary

Over the last 15 years, selective pre-fluxing – also called paint fluxing or binder-based fluxing – has evolved as an alternative method for applying flux powder in aluminium brazing industry. There are many activities to define process parameters of fluxing with adhesives.

The first part of this paper outlines key features of pre-fluxing. The methodology for measurements of physical characteristics of binders and paint flux mixtures are described. General rules for behaviour of flux paints in brazing process are discussed together with some examples of flux paint features.

In the second part a case study is shown to illustrate common challenges when brazing with flux paint. The last part of this paper provides a cost comparison as guidance for choosing the right fluxing method for two different cases, one being extremely negative and the second as a positive case.

3. Overview of Binders

Group Adhesion providing components Co-solvents / dispersion agents (examples only) Carriers / solvents
1 Polyurethane (aqueous polyurethane dispersion) N-Methyl-2-pyrrolidon water
2 Water-based acrylic 3-Methoxy-3-methyl-1-butanol water
3 Solvent-based acrylic 1-Methoxy-2-propyl acetate and others Preferably non-explosive and non-flammable organic solvents (e.g. esters of dicarboxylic acids)

Table 1: Main groups of flux binders / flux paints.

One of the most important characteristic of a binder is the kinetics of binder removal. This property is measured by a method called Differential Thermal Analysis [DTA]. The specimen (binder or flux paint) is placed in a small crucible and heated with a preset rate. The device measures the change of weight of the specimen and heat emitted or absorbed by the sample. The test can be done in air or at a chosen gas atmosphere.

An example of the curves obtained in such device is shown in Fig. 1

Fig. 1: DTA curves obtained from solid flux paint sample. Test performed in air. 

The upper curve represents lost of weight upon heating, and the lower curve represents thermal effects appearing in the heated sample. The endothermic effect is associated with evaporation of the sample and the exothermic effect is usually connected with burning of the sample.

It should be observed that the above curves represent a sample of liquid flux paint. The removal of the the liquid phase (carrier evaporation) takes place during curing of the painted part. This process is always done before putting the parts into the brazing line. For flux paints made with water as a carrier it is simple evaporation.

Removal of the solid phase (cured binder) takes place at much higher temperature then evaporation of the carrier. It usually happens in the brazing line – in the dryer and partially in the brazer. Kinetics of the solid phase removal is shown in Fig. 2. In this case the analyzed sample is prepared by painting a metal surface, curing the paint and careful scratching off the solid paint, which is then analyzed in DTA device.

Fig. 2: DTA curves obtained from liquid flux paint sample. Test performed in air. 

As can be seen the end of the binder removal is in the temperature range of 450oC. The above presented curves show the removal of binder at a constant heating rate of the sample (in this case 10oC/min). In the brazing line the prefluxed parts firstly go through a dryer where the temperature for dry parts is usually in between 200oC to 250oC. The parts for a continuous brazing line usually stay in the dryer no longer than 10 minutes.

To simulate this condition, a dry flux paint sample was analyzed by DTA with a hold for 10 minutes at 300oC. As can be seen from Fig. 3, holding at constant temperature for a prolonged time does not lead to full removal of the binder. In the given case only about 36% of the binder was removed.

 Fig. 3: DTA curves with holding time 10min. at 300oC Test performed in air.

Different furnace design and different size of the brazed parts are responsible for different heating kinetics in the brazing lines. An influence of different heating rates on kinetics of binder removal is shown in Fig. 4.

Fig. 4: DTA curves with different heating rates Test performed in nitrogen. 

The curves presented in Fig. 4 were obtained from analyzing a polyurethane binder heated in nitrogen atmosphere. It can be seen that only the middle temperature is moved to higher values with increased heating rate. The beginning and end of the debinding process do not depend on the heating rate.

Several examples of debinding temperatures for different type of binders are presented in table 2.

Binder Type Tested in Air Tested in Nitrogen
Middle temp. [°C] End Temp. [°C] Weight loss [%] Middle temp. [°C] End Temp. [°C] Weight loss [%]
Polyurethane Binder A 355 530 99.7 370 460 99.6
Polyurethane Binder B 360 550 98.5 370 460 97.5
Acrylic Binder C (water soluble) 317, 382 450 87.2 220, 387 430 85.2
Acrylic Binder D (high adhesion) 267 420 Not measured* 385 Not measured* 27.5
Acrylic resin Binder E 275 400 86.9** 370 450 89.3**
* DTA performed only on ready mixtures
**Lower values due to some flux residue (sample obtained from ready mixture)

Table 2: Examples of debinding temperatures for different types of binders.

Will be continued soon.

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Preparation and Agitation of Flux Slurry

Preparation

In the simplest operation, the lid is removed and flux is manually scooped out of the drum (with a  large plastic scoop) and added to the flux slurry reservoir tank. The flux should always be added to water and never scooped into an empty tank. Aerosolization should be controlled by a local exhaust ventilation system (LEV). The operator will likely need to wear a dust respirator and PVC gloves, goggles and an adequate protective coverall.

For large volumes of flux slurry preparation, it is also common to dump the entire drum contents into the reservoir with a forklift truck. Again, care should be taken to avoid dusting and aerosolization.

All slurries must be agitated to hold the flux particulate in suspension. Allowing the flux particles to settle out in the mixing tanks or containers will result in inconsistent flux loadings. During a shutdown period (maintenance, holidays etc.), the agitators may be turned off. Upon start up, it must be ensured that all settled flux is brought back into suspension prior to starting the fluxing operation. Ideally, the flux slurry should be slowly agitated during shutdown for ease of start-up.

Agitation

Since the flux is insoluble in water and the goal is to keep the flux in suspension, the natural tendency is to use high agitation speeds which creates high shear forces. The high shear forces will break up particles of flux and over time (even a few hours), shift the particle size distribution to smaller particles, even to the sub-micron range. These very small particles tend to be „sticky“ and when collected in one place, will acquire a gel like appearance. Furthermore, once the flux has acquired this sticky property, it is very difficult to bring this flux back in suspension after a shut-down period.

These effects may be seen even if the speed of the agitator has not changed, but the slurry consumption has decreased (e.g. one less work shift per day). In other words, the same flux is being agitated for a longer time than before and therefore may be shifting to a smaller particle size as a result of the increased residence time in the tote.

The key to agitation for flux slurries is low speed – low shear agitation to just keep the flux in suspension. Faster is definitely not better when it comes to keeping the flux slurry suspended.

Flux which has acquired a gel like consistency caused by high shear stresses may lead to strainer clogging. Even if the individual particles are small enough to pass through the mesh, once one particle sticks to the screen, others will stick to it and eventually accumulate to such an extent as to clog the strainer. Gelled flux is very difficult to bring back into suspension because it does not break up easily – the flux sticks to itself. This gelled flux will clog a small mesh size strainer in no time at all. The stickiness of sub-micron particle size flux has been associated with many blockages and is often seen to clog nozzles.

Large agglomerates are most often formed by the flaking off of flux that has dried on the walls of the spray cabinet or other nearby structures such as exhaust hoods. The best practice to avoid the formation of these agglomerates is to have a regular clean-out procedure. When this practice is not carried out, flux solids will settle out within individual droplets and form clumps or agglomerates. These agglomerates can be very hard and are also often associated with blockages.

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Paint Fluxing – Pros and Cons, Part 1

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Selective Pre-Fluxing with Adhesives – Fashion or Progress

Summary

Over the last 15 years, selective pre-fluxing – also called paint fluxing or binder-based fluxing – has evolved as an alternative method for applying flux powder in aluminium brazing industry. There are many activities to define process parameters of fluxing with adhesives.

The first part of this paper outlines key features of pre-fluxing. The methodology for measurements of physical characteristics of binders and paint flux mixtures are described. General rules for behaviour of flux paints in brazing process are discussed together with some examples of flux paint features.

In the second part a case study is shown to illustrate common challenges when brazing with flux paint. The last part of this paper provides a cost comparison as guidance for choosing the right fluxing method for two different cases, one being extremely negative and the second as a positive case.

1. Introduction

In aluminium brazing industry fluxing is one of the most important steps in the production process. Flux water slurry application is considered as a standard and as a matter of fact very robust methodi. We believe that about 70% of overall fluxing activities are done by flux water slurry spray. This method has however certain disadvantages like troublesome slurry preparation and requirements for large and sometimes expensive machinery.

In order to lower production costs, new fluxing technologies have been introduced. One of them is called paint fluxing or binder-based fluxing which allows for elimination of wet fluxing process from the brazing line. Actually, the prefluxing process can be even done by an external company/subcontractor. It is nevertheless still a process of coating, which is done to particular component surfaces of the whole assembly – usually before the components are assembled.

In the industrial practise – particularly when one is in contact with many different users of the prefluxing technology – it is quite important to define the basic features and properties of discussed technology.

Flux Painting Booth

Flux Paint:
A mixture of brazing flux with binder, demineralised water or organic solvent, and thickener (the latter not always obligatory)

Binder:
Organic complex compounds, which are activated by curing – to provide adhesion of flux particles to the painted surface.

Thickener:
Organic substance, which is used to adjust viscosity and to facilitate re/mixing of the flux paint.

Curing:
Drying of the painted parts – usually with a blow of hot air (about 150°C). During that process liquid carrier (water or organic solvent) is evaporated and binder becomes activated to provide adhesion.

Adhesion:
Qualitative or quantitative measure by which strength of the flux particles bonding to the painted surface is determined. There are many different methods to describe adhesion of the flux paint. At Solvay we are using a simple quantitative method: A coated and cured coupon is placed in a holder positioned on a scale, a steel wedge is moved along the coupon with a gradual pressure increase. The weight at which the first scratches appear is a numerical value for adhesion.

Debinding:
Removal process of the binder from the painted surface done by treatment with high temperature, either in air or in ambient atmosphere.

Binder must be removed before reaching brazing temperature; otherwise the carbon residue will interfere with the brazing process – leaving both black stains on the part surfaces and very often leading to lack of brazing. Removal of the binder is done by applying high temperature to the assembled parts. In most cases the process of binder removal is realized in the brazing line both in the dryer and brazer.

2. Basic Rules for Flux Painting

The process of coating can be done by spraying, roller coating, brushing, or dipping. Uniformity of coating is very important, any agglomerates and lumps must be avoided. The flux paint can be prepared without thickener. Practically it is required in the mixture when a longer storage is expected (i.e. more then few days). There is an optimal temperature for curing resulting in maximum adhesion. Curing at ambient temperature is possible, but it will yield lower adhesion. Curing at too high temperature can lead to significant loss of adhesion.

Apart from the curing condition, adhesion also depends on the ratio of binder in the mixture (the more binder in the mixture the stronger adhesion), and the type of the binder (as a rule of thumb: the higher flash point of the binder the stronger adhesion). The most common method for prefluxing with binder mixture is using an atomized spray method on a machine which performs degreasing, painting and curing.

Will be continued soon.

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Flux Application: Electrostatic Fluxing

This technique, also known as dry fluxing is gaining popularity as an alternative fluxing practice and therefore will be described here in some detail. Dry fluxing is a technology whereby the flux is electrostatically charged and applied to a grounded work piece, in our case a heat exchanger or individual heat exchanger components. The electrostatic attraction causes a layer of flux to be deposited on the work piece. A typical flux application system consists of a powder feed system, the electrostatic spray gun, the gun control unit, the grounded work piece and finally the flux recovery system.

The advantages of such a system over conventional wet fluxing are evident. Since the flux is applied dry, there is no need to prepare flux slurries, hence no need to monitor flux slurry concentrations. There is also no wastewater generated therefore more environmentally friendly. The dehydration or dry-off section of the furnace may be eliminated since the heat exchangers enter the furnace already dry. However, one must keep in mind that this is a relatively new fluxing technique and there are some minor drawbacks. Flux adhesion is not as good compared to that of wet fluxing. The flux also tends to accumulate on the leading edges of the heat exchanger and because of the Faraday cage effect, may have some difficulties in coating into corners or more specifically, in tube to header joints.

Powder Feed Systems
Presently, there are two types of powder feed systems on the market. The first type begins with the flux being fluidized in a hopper. Dry compressed air is fed through a porous membrane in the bottom of the hopper. The air rising through the volume of flux makes it behave like a fluid since the powder is essentially diluted with air. A pick up tube attached to an air pump is extended in the fluidized flux. Powder flow is then regulated by controlling the air-flow to the pump which is then delivered through the feed system to the spray gun. This type of feed system works perfectly well for powder paints. However, the flux has very different physical characteristics than powder paints (particle size, morphology) and so is difficult to fluidize. This must be taken into consideration when the manufacturer designs a powder feed system that relies on fluidization.

Dry Fluxing – Mechanical Flux Transport

The second type of powder feed system works on the principle of mechanical delivery or positive displacement. This means that the powder feed rate to the air pump is controlled by a screw or auger. The flux is contained in a main feed hopper and delivered mechanically at a controlled feed rate to the air pump. Powder flow is thus regulated by controlling the auger feed rate. This powder feed system does not rely on the flux being fluidized. Nonetheless, modifications over conventional mechanical powder feed systems are still necessary to overcome the differences between the flux characteristics and conventional powder paints.

Dry Fluxing – Powder Fluidization

Japanese heat exchanger manufacturers have used the technique of dry fluxing for many years now. Within the last few years, North American and European manufacturers have also installed electrostatic fluxing stations. Experience with this technique is being accumulated at a rapid rate, given that the equipment manufacturers and flux suppliers are taking an active role in improving the technology.

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Fixture for braze assembly during brazing

Considerations
Fixtures are used to hold the braze assembly in place during brazing. Surfaces with molten filler metal are very “greasy” and the fixtures need to hold the shape and tolerances during heat-up. Fixtures may also be used to support attachments such as inlet or outlet tubes.
When considering the type or configuration of fixtures to use, there are a number of considerations to take into account. For example, differential expansion between fixture and braze assembly increases part compression significantly during heat-up. One must be acutely aware of the differences in the coefficients of thermal expansion between stainless steel and aluminum. Aluminum expands much faster than stainless steel and this must be taken into consideration when designing a fixture. This is important to prevent distortion of the heat exchanger at final brazing temperature.
It is also important to note that molten filler metal dissolves steel and stainless steel. It is important to minimize contact with filler metal. It is also possible for aluminum to braze to fixtures. It is therefore important to either use a brazing stop-off for surfaces in contact with aluminum or to oxidize the fixtures when new or after cleaning. This can be done simply by running the fixtures through the brazing furnace.

Permanent Fixtures
The most common type of fixtures for heat exchanger manufacturing are permanent fixtures, ones that are used over and over again. These are usually made and should be made from stainless steel to prevent rust contamination in the slurry tank. The preferred material for fixtures is AISI 309 or 316, but most stainless steel alloys are perfectly acceptable.
Springs may be used in the fixture to apply a certain “holding” pressure to the heat exchanger during brazing. However, the technique of using springs seems to be less common than in the past. More often now, fixtures are designed with fixed dimensions. The heat exchanger is compressed slightly and loaded into the fixture. When the source of compression is removed, the natural spring-back holds the heat exchanger in place against the fixture.

Cleaning
As flux builds up on permanent fixtures and may contaminate the flux slurry, it is necessary to routinely clean the fixtures to remove flux and other contaminants that may have accumulated. There is no convenient chemical cleaning method to remove flux residues. The most appropriate methods are by mechanical means such as wire brushing or grit-blasting.
Once the residues have been removed by one of the above methods, the fixtures should be oxidized by running them through the brazing furnace. Non-oxidized fixtures are likely to stick or even braze to the work piece.

Steel banding
An alternative to permanent fixtures is the use of disposable steel banding. Since mild steel can be used, material costs are kept to a minimum. Wax coated mild steel bands are often used to prevent the banding material from rusting that can contaminate the flux slurry and discolor the heat exchanger. The steel bands are used only once and are disposed of after brazing.
Steel banding requires experimentation to determine the appropriate tension and positioning. Thereafter, an automatic banding machine should be used to ensure consistency.

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Metallographic Sample Preparation and Examination of Brazed Heat Exchangers

Sample Preparation – Orientation

The heat exchanger chosen for the purpose is a NOCOLOK Flux brazed radiator. To provide some orientation as to where the metallographic sections will be taken from, Figure 1 shows the water-side header area (top) and part of the finpack, sidesupport and header area.

Figure 1

In most metallographic investigations of brazed heat exchangers, the critical joints to examine are the tube-to-header joints and the fin-to-tube joints. For instance, a leak in a tube-to-header joint constitutes a failure. The fin-to-tube joint on the other hand, although not as critical as the tube-to-header joint, is the key area where heat transfer takes place. It is therefore necessary that the fin-to-tube joints are metallurgically bonded (i.e. brazed) for maximum heat transfer efficiency.

Sample Preparation – Sectioning

With a band saw, the radiator can be cut down through the center of the tubes (see Figure 2). This will keep the fins intact. If necessary, one can saw through the fins if the blade is kept as close to the outer tube wall as possible. That is the outer tube wall can be used to guide the saw blade. Otherwise, it is better to saw through the center of the tube where the inner walls will act as the guide.

Figure 2

Once the above sections have been obtained, the samples can be sawn longi-tudinally through the center of the tube and header as shown in Figure 2, right. The tube-to-header and tube-to-fin sections can then be cut. The size of the cut samples must fit inside a 30 mm or 40 mm mount.  Note that it is the cut face that will be grinded and polished.

Grinding and Polishing

The following section shows what the sample actually looks like after each grinding and polishing step. The intention is to help the metallographer track the progress of grinding and polishing with the help of visual aids.

Figure 3 shows what a section of „unbrazed“ brazing sheet looks like under the microscope after wet grinding with 220, 500 and 1000 grit SiC paper. In each case, the sample is ground until all the grinding lines appear in the same direction, across the entire grinding face. It also helps that the grinding lines go in the direction of, or perpendicular to the area of interest. In this case, the grinding lines all run perpendicular to the braze sheet after 220 grit paper. After 500 grit paper (rotating the sample 90°), the grinding lines all run parallel to the tube and after 1000 grit, once more perpendicular to the braze sheet.

Figure 4 shows what the braze sheet looks like after each successive polishing step. After the 6 µm diamond suspension, the microstructure of the braze sheet becomes visible (more on microstructure later). At this stage, there are still a number of scratches. After the 3 µm diamond suspension, the micro-structure is clearer and there are less scratches.  Only after the colloidal silica are all scratches removed. The 64x magnification in Figure 4 is too small to reveal fine micro-structural details after the colloidal silica polish, but what is evident is that the braze sheet is now highly polished and scratch free.

Figure 3


Figure 4

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New glass brazing furnace

Article from the Newsletter of our sponsor Solvay Fluor:
New glass brazing furnace in the NOCOLOK Technical Center

Many visitors to seminars, trade shows or videos are already familiar with the test glass brazing furnace in the NOCOLOK Technical Center. The unique furnace now has a big brother. All components of the new test furnace, except for the radiant heater, were developed in own production at Solvay.

The fluorine research workshop in Hannover has done an excellent job, “The construction of such a furnace is only possible with the tremendous expertise of the colleagues in the test workshop,” says Andreas Becker, a Solvay Fluor research employee. “With the new glass furnace, it is possible to braze larger objects, such as aluminium wafers for refrigerant test series for automobile producers.”

Specially developed software can capture every stage of the brazing process as high-resolution images – so that not even the tiniest detail of the brazing process can escape the testers. The new furnace saves energy and time – test brazing series with larger objects no longer require the much larger Camlaw brazing furnace at the Technical Center.

The next stage of development is already being planned: in a unique process Solvay’s glass blowers have succeeded in forming a square glass body, which offers even more space for larger items.

An overview of all services from the NOCOLOK Technical Center is offered in the new brochure, which is available for download.

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Filler Metal Management 2

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Case Study

A radiator core retrieved from service was examined for a suspected premature corrosion related failure.
Upon closer metallographic examination, no evidence of corrosion was found at the failed area.

33% tube core erosion in the failure area


Header: AA4343/ AA3005

Tube: AA4343/ AA3003
 
 
 
 
 
 
 
 
It was concluded that the cause of the failure was in fact a mechanical failure occuring in the thinned wall area.

The following sequence of events proposes a rational explanation for the eroded tube area:

In service radiators are subject to internal pressure fluctuations and expansion and contraction due to heating and cooling. Mechanical failure was imminent and occured in the weakest part of the tube, the thinned down tube wall area adjacent to the tube to header joint.

Conclusions

Erosion of the base metal is undesirable since it reduces the wall thickness of the brazed component.
In addition Si penetration in the grain boundaries is known to increase the susceptibility to intergranular corrosion. Therefore proper filler metal management practices should be observed to prevent undesirable effects. One such factor easily controlled by the brazer is maximum peak brazing temperature.

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