Introduction of NOCOLOK® Cs Flux (SM)
as Synthesized Material

Apr 27
2017

What is NOCOLOK® Cs Flux (SM)? (Synthesized Material)

NOCOLOK® Cs Flux is used for brazing of aluminium alloys with higher magnesium levels. The Cs flux currently available for CAB (Controlled Atmosphere Brazing – furnace brazing) is a technical mixture (i.e. a mechanical blend) of K-Al-F flux (NOCOLOK® Flux) with Cs-Al-F flux – this product is offered under the name NOCOLOK® Cs Flux (TM): Technical Mixture. 

The new NOCOLOK® Cs Flux (SM) is a fully synthesized material – i.e. a unique and homogenous product. The Cs is completely embedded in a Cs-K-Al-F matrix during the manufacturing process.

Advantages

When comparing the characteristics and application of blended Cs Flux “(TM)” with synthesized material “(SM)”, there are notable advantages of the new quality:

  • The mixture can show settling and separation in flux slurries and paints.  This is caused by differences in the density, the particle size, and the solubility of the two compounds in the blend.
  • In the new fully synthesized material – with the Cs completely incorporated in a Cs-K-Al-F matrix – the density is consistent and the particle size more uniform.  We have a homogeneous powder with improved stability in suspensions (i.e. for slurries, paints, and pastes).
  • In addition, the overall solubility is reduced when compared with the blended material.
  • There will be less settling and less separation – which means that there is  enhanced application performance with NOCOLOK® Cs Flux (SM).

NOCOLOK® Cs Flux (SM) is on stock at our Wimpfen facility and available right away. 

Worldwide Registration

For a number of years, more and more countries are converting their existing chemical regulations or are implementing new regulations. In many cases, these regulations ​c​an be considered as an adaption of the European REACH Regulation. A registration of chemical substances or reaction masses is required, including comprehensive material data sets and risk assessment. 

Solvay appreciates and supports these new product safety initiatives.
As a consequence, however, this leads to that in order to fulfill all regulatory requirements new products can only be introduced stepwise to other countries.

NOCOLOK® Cs Flux (SM) has already been successfully registered according to the European REACH Regulation and can be used without restriction within the European Union. Please also refer to our Safety Data Sheet, which is available on request. Registration for other countries/regions will be done successive. For more information, please contact our local sales offices.​

 

 

Flame Brazing Technology – Part 3

Jan 29
2016

U‐shape brazing alloys with flux integrated into material

u-rings-picture

Advantages

  • Reduced labor cost
  • Reduced waste
  • No post-braze cleaning
  • Flexible design
  • Multiple applications
  • Ideal geometry for feeding
  • No hidden flux voids
  • Precise control of alloy and flux

 

Ideal for Preforms

  • Unlimited preform options
  • Flux flows unobstructed

u-rings-drawing

NON‐CORROSIVE FLUX

No post braze cleaning required, reducing the environmental impact associated with waste water

treatment

LESS CONTAMINATION

there are no powders leaching out to contaminate assembly equipment. The flux we deposit in the

channel stays in the channel.

Microsoft PowerPoint - HPa Flame brazing.pptx

Download the brochure.

To be continued…

Flame Brazing Technology – Part 2

Dec 21
2015

Selecting the Correct Flux –WHAT?
The first requirement of an Aluminium brazing is to be chemically effective.
Fluxes are categorized as active (corrosive) and inert (noncorrosive).

Fluoride base fluxes → NON‐CORROSIVE
The fluxes leave the white gritty residue on the part. These fluxes include the higher temperature potassium
aluminium fluoride and the lower activated cesium aluminium fluoride Fluoride flux residues is tightly adhered to aluminium surface, relatively insoluble, not necessary to be removed. Fluoride flux operates by melting, spreading and dissolving of aluminium oxide layer.

Active fluxes ‐ Chloride base fluxes → CORROSIVE
The appearance of the part after brazing is bright and shiny. The chloride post braze residues must be removed by water washing or chemical treatment, to prevent the occurrence of electrolytic corrosion. These fluxes require a significant exposure to hot water to remove the corrosive flux residues. Attention must be given to the outside of the assembly and to any residues that have migrated to the inside of the part.
Chloride flux is reported to work penetrating aluminium oxides at weak points and breaking up the oxide/aluminium bond.

Selecting the Correct Flux –WHY?
Effect of Mg content on mechanical properties and braze ability of Al‐alloys.

Microsoft PowerPoint - HPa Flame brazing.pptx

0,3‐0,6% Σ(Mg+Cu)% -> 2% cesium flux
0,6‐0,9% Σ(Mg+Cu)% -> 6‐10% cesium flux
0,9‐2% Σ(Mg+Cu)% -> 100% cesium flux
>2% Σ(Mg+Cu)% -> 726/0726 pastes

Correct filler metal / Correct flux
Fluxes must be thermally matched to the melting phase of the braze filler base metal.

Microsoft PowerPoint - HPa Flame brazing.pptx

CORROSIVE flux paste for the flame brazing of aluminium materials
Al‐FLUX 0726/2zG – Flux Paste
• As the active component of Corrosive‐Flux‐Paste, AL‐Flux 0726 contains a mixture of LiCl,
NaCl, KCl, inorganic‐ and complex‐ fluorides.
• Organic carrier systems are used to prepare a wide range of pastes for the flame brazing of
aluminium materials.
• Al‐Flux 0726 Flux Paste is typically applied by dispensing and brushing for flame brazing. No
component mixing is required. Products are supplied as ready to use products, requiring short
remixing

Download product information.

NON‐CORROSIVE Flux Paste for the flame brazing of aluminium materials
NOCOLOK® 028/55 Cs2 ‐ Flux Paste
NOCOLOK® 028/55 Cs3 ‐ Flux Paste
NOCOLOK® 028 CsD ‐ Flux Paste
From low‐temperature brazing (450°C) to the brazing of high‐strength aluminium alloys.

Download product information.

To be continued…

Flux Residue – Part 4

Jan 14
2015

Approach to non-corrosive fluxes for further reduced residue solubility and improved magnesium tolerance
Technical Information by Ulrich Seseke-Koyro, Hans-Walter Swidersky, Leszek Orman, Andreas Becker, Alfred Ottmann
We split the article in four parts:

  1. Abstract and Basic Experimental Laboratory Procedures
  2. Reduced Flux Residue Solubility
  3. Improved Magnesium Tolerance
  4. Summary and Outlook

Summary

Our research activities so far have been focusing on flux blends with additives to validate lower water solubility of post braze flux residue. Another objective of this work was to allow for brazing of Al alloys with increased Mg levels using non corrosive fluxes.

First steps have been made with selected flux blends.  This paper reflects the current project status, but more work still needs to be done for further improvement.

Low flux residue solubility

It has been shown that the flux residue water solubility is reduced by combining KAlF4 with AEFs (“KAlF4 compound concept”); among them BaF2 being the most promising candidate.

Fluxes for higher Mg tolerance

Flux blends containing KAlF4 plus CsAlF4 and Li3AlF6 seem to be a promising approach to improve brazing of higher Mg containing aluminium alloys.

Aluminium coupons samples (AMAG 6951 with 0.68% Mg) for the base coupon and the angle (1.36% Mg in the joint interface) require flux loads as high as 15g/m2 for successful brazing.

Good joint formation can be achieved at 5g/m2 load on samples with 0.68% Mg content. Thus brazing of higher Mg level Al-alloys with appropriate flux mixtures at process-typical loads seems to be feasible.

Outlook

For the continuation of this project, we need to define the Mg range for real industrial aluminium heat exchanger needs. We think that this can best be done in a joint effort of HX manufacturer, Al material supplier and flux producer.


  1. P Garcia et al, Solubility Characteristics of Potassium Fluoroaluminate Flux and Residues, 2nd Int. Alum. Congress HVAC&R, Dusseldorf (2011)
  2. P Garcia et al., Solubility and Hydrolysis of Fluoroaluminates in Post-Braze Flux Residue, 13th AFC Holcroft Invitational Aluminum Brazing Seminar, Novi (2008)
  3. J Garcia et al, Brazeability of Aluminium Alloys Containing Magnesium by CAB Process Using Cs Flux, VTMS5, 2001-01-1763 (2001)
  4. H Johannson et al, Controlled Atmosphere Brazing of Heat Treatable Alloys With Cesium Flux, VTMS6 C599/03/2003 (2003)
  5. Handbook of Chemistry and Physics; Ref. BaSO4: 0.0025 g/l
  6. U Seseke, Structure and Effect – Mechanism of Flux Containing Cesium, 2nd Int. Alum. Brazing Con., Düsseldorf (2002)

Flux Residue – Part 3

Dec 05
2014

Approach to non-corrosive fluxes for further reduced residue solubility and improved magnesium tolerance
Technical Information by Ulrich Seseke-Koyro, Hans-Walter Swidersky, Leszek Orman, Andreas Becker, Alfred Ottmann
We split the article in four parts:

  1. Abstract and Basic Experimental Laboratory Procedures
  2. Reduced Flux Residue Solubility
  3. Improved Magnesium Tolerance
  4. Summary and Outlook

Improved Magnesium tolerance

Mg additions to Al alloys contribute to higher strength properties. The ongoing trend in saving weight by down-gauging of Al sheet thickness requires sufficient mechanical stability. One option for the production of higher strength Al alloys is to increase the Mg content.

A disadvantage of Mg is the interaction with potas-sium fluoroamuminate fluxes during brazing, which results in poor joint formation [3] [4]. This effect, known as “flux poisoning”, is caused by the formation of high melting compounds. The addition of caesium and other metals to the flux helps to compensate to a certain degree the poisoning [6].

For the first set of laboratory brazing experiments we chose commercially available AMAG 6951 brazing sheet (0.68% Mg, 4343 clad) and clad-less AMAG angle material (0.68% Mg) to investigate the brazing performance and joint formation. In this situation the metal-to-metal interface adds up to 1.36% Mg (2 x 0.68%) in total.

Table 1 shows a list of representative flux combina-tions with NOCOLOK® types, KAlF4, Li3AlF6. CsAlF4, and AEFs.

We repeated all brazing tests with each sample three times.

Flux Type Load Fillet visual validation Comment
NOCOLOK® Cs Flux 10 g/m2 100% very small joint inconsistent seam
MD001212 LiCs24 10 g/m2 100% small joint weak seam
MD001223 LiCs43 10 g/m2 86% small joint inconsistent seam
AB039215 KAlF4/BaF2 10 g/m2 52% small joint inconsistent seam
NOCOLOK® Cs Flux 15 g/m2 100% weak seam
MD001212 LiCs24 15 g/m2 100% thicker than with NOC Cs Flux
MD001223 LiCs43 15 g/m2 100% thicker than with NOC Cs Flux
AB039215 KAlF4/BaF2 15 g/m2 98% weak seam slighly better than NOC Cs Flux

Table 1: Brazing trials: AMAG clad – AMAG clad-free angle different flux blends based on KAlF4 plus BaF2/Li3AlF6/CsAlF4

The angles from most of the AMAG specimens could be removed after brazing by pulling. Only a broken inner and outer fractured seam line was left – as can be seen below in picture 1 a.
flux_residus_part3_1
flux_residus_part3_2
flux_residus_part3_3

Picture 1: a) Photos, b) and c) SEM/EDX of NOCOLK® Cs Flux brazed sample (load 15 g/m²) Coupon 0.68% Mg, angle 0.68% Mg – angle removed by pulling

From the SEM analysis it is evident that a proper met-allurgical joint between base and angle has not been formed.

flux_residus_part3_4
flux_residus_part3_5

Picture 2: SEM/EDX analysis of aluminium ‘angle on coupon‘ brazed with KAlF4/BaF2 blend

There is flux residue present in the pulled apart fillet. This indicates that the liquid filler alloy was not capa-ble of pushing out completely the flux of the joint and it could be an explanation for the weakness of the fillet.

However, in case of the blend MD001212 LiCs24 with load 15g/m2 the joint structure is thorough as can be seen in picture 3 a).

flux_residus_part3_6

Picture 3: Microstructures of the brazed joints
a) Flux MD001212, load 15g/m2
b) Flux MD001223, load 15g/m2

It is worth mentioning when connecting blocks are brazed to condenser manifolds often a high load of manually applied flux is used in order to overcome the high Mg content in the block material. For such a case using the mixture MD001212 would allow for having quite high Mg content in the block material, which can be required by the designers of condens-ers.

The total concentration of 1.36% Mg (joint interface) is probably too high, because for most brazing applica-tions, a flux load of 15g/m2 is impractical. Thus, we decided to reduce the level of Mg in our samples to half – i.e. to 0.68% – by switching to an AA1050 (Al 99.5%) angle. We also reduced the flux load to a more process-typical level of 5g/m². The results are listed in table 2:

Flux Type Load Fillet visual validation Comment
MD001212 LiCs24 5 g/m2 100% good seam
NOCOLOK® Cs 5 g/m2 87% small joint

Table 2: Brazing tests AMAG coupon (0.68% Mg)/Al99.5 angle

The structure of the joint cross section below (picture 4) obtained with flux MD001212 LiCs24 shows good quality.

flux_residus_part3_7

Picture 4:Joint cross sections of alloys containing 0.68% Mg brazed with MD001212 LiCs24, load 5g/m2

To be continued…


  1. P Garcia et al, Solubility Characteristics of Potassium Fluoroaluminate Flux and Residues, 2nd Int. Alum. Congress HVAC&R, Dusseldorf (2011)
  2. P Garcia et al., Solubility and Hydrolysis of Fluoroaluminates in Post-Braze Flux Residue, 13th AFC Holcroft Invitational Aluminum Brazing Seminar, Novi (2008)
  3. J Garcia et al, Brazeability of Aluminium Alloys Containing Magnesium by CAB Process Using Cs Flux, VTMS5, 2001-01-1763 (2001)
  4. H Johannson et al, Controlled Atmosphere Brazing of Heat Treatable Alloys With Cesium Flux, VTMS6 C599/03/2003 (2003)
  5. Handbook of Chemistry and Physics; Ref. BaSO4: 0.0025 g/l
  6. U Seseke, Structure and Effect – Mechanism of Flux Containing Cesium, 2nd Int. Alum. Brazing Con., Düsseldorf (2002)

Flux Residue – Part 2

Oct 21
2014

Approach to non-corrosive fluxes for further reduced residue solubility and improved magnesium tolerance
Technical Information by Ulrich Seseke-Koyro, Hans-Walter Swidersky, Leszek Orman, Andreas Becker, Alfred Ottmann
We split the article in four parts:

  1. Abstract and Basic Experimental Laboratory Procedures
  2. Reduced Flux Residue Solubility
  3. Improved Magnesium Tolerance
  4. Summary and Outlook

Reduced Flux Residue Solubility

The water solubility of standard NOCOLOK® Flux is 4.5 g/l, whereas for post-braze flux residue (pbr) it is 2.7 g/l. Post-braze residue of NOCOLOK® Li Flux shows a solubility of 2.2 g/l [1].

In the periodic table of chemical elements the group I fluorides have a reasonable low solubility (LiF: 2.7g/l [20°C]), but their Al-F-complexes much lower (Li3AlF6: 1.1g/l , K2LiAlF6: 0.3g/l with about 183 mg F-/l, K3AlF6: 2g/l), the group II fluorides (Alkaline Earth Fluorides “AEF”) show very low solubility (MgF2: 0.13g/l, CaF2: 0.016g/l, SrF2: 0.12g/l [25°C], BaF2: 0.12g/l [25°C]) [5]. Based on the facts of the dissolution behaviour of NOCOLOK® Li and the much lower solubility of the AEFs, we started investigating combinations of potas-sium fluoroaluminate fluxes with selected AEFs to combine the brazing characteristics of NOCOLOK® type flux with the very low solubility of AEF.

NOCOLOK® Flux consists of potassium fluoroalumi-nates with a specific ratio of KAlF4 and K2AlF5. Each of these compounds has different solubility. The combination of the (pure) compounds with different AEFs was of our main interest. We melted and pulverized the flux blends, dissolved them in a defined amount of DI-water and analyzed for K, Al and F.

The data achieved form these experiments is illus-trated in figure 1:

Flux-Residue-dia-1

Fig. 1: Solubility of flux blends – melted and pulverized
(lines are used to illustrate differences of the blends)

Considering minor statistical variations, the results look quite reasonable, with the blend of NOCOLOK® Li/BaF2 showing the lowest K value. This observation can be explained by the low solubility of NOCOLOK® Li Flux. Of more relevance is the actual post-braze solubility (flux residue) on brazed Al surfaces. Interactions of base material and molten filler metal may have a more complex chemical impact on the solubility behaviour

The results from coupon brazing under laboratory conditions and the solubility of the flux residue can be seen in figure 2.

Flux-Residue-dia-2

Fig. 2: Post-braze fluoride solubility of selected flux/ AEF combinations on Al coupons
(lines are used to illustrate differences of the blends)

Among the combination of NOCOLOK® type fluxes with diverse AEF additions, KAlF4/BaF2 shows the lowest residue F– solubility, i.e. 4mg/l. All our laboratory brazing tests with the samples showed the same good results like with standard NOCOLOK® Flux.

Corrosion comparison tests will be subject for future investigations.

To be continued…


  1. P Garcia et al, Solubility Characteristics of Potassium Fluoroaluminate Flux and Residues, 2nd Int. Alum. Congress HVAC&R, Dusseldorf (2011)
  2. P Garcia et al., Solubility and Hydrolysis of Fluoroaluminates in Post-Braze Flux Residue, 13th AFC Holcroft Invitational Aluminum Brazing Seminar, Novi (2008)
  3. J Garcia et al, Brazeability of Aluminium Alloys Containing Magnesium by CAB Process Using Cs Flux, VTMS5, 2001-01-1763 (2001)
  4. H Johannson et al, Controlled Atmosphere Brazing of Heat Treatable Alloys With Cesium Flux, VTMS6 C599/03/2003 (2003)
  5. Handbook of Chemistry and Physics; Ref. BaSO4: 0.0025 g/l
  6. U Seseke, Structure and Effect – Mechanism of Flux Containing Cesium, 2nd Int. Alum. Brazing Con., Düsseldorf (2002)

Flux Residue – Part 1

Sep 04
2014

Approach to non-corrosive fluxes for further reduced residue solubility and improved magnesium tolerance

Technical Information by Ulrich Seseke-Koyro, Hans-Walter Swidersky, Leszek Orman, Andreas Becker, Alfred Ottmann

We split the article in four parts:

  1. Abstract and Basic Experimental Laboratory Procedures
  2. Reduced Flux Residue Solubility
  3. Improved Magnesium Tolerance
  4. Summary and Outlook

Abstract

 

For more than 30 years, potassium fluoroaluminates (NOCOLOK®) fluxes are already successfully used in controlled atmosphere brazing (CAB) of aluminium heat exchangers. Residues of these so-called non-corrosive fluxes have very low – but evident – solubility in water [1] [2]. In the discussion about corrosion of CAB produced aluminium heat exchangers, the flux residue solubility is an important parameter. There are concerns that – in addition to several other factors – fluoride ions (F–) potentially released from dissolved residue play a role in aluminium corrosion.

A theoretical option to address this point is the development of virtually insoluble flux. More realistic, however, will be fluxes with less soluble residues than the current compositions.

Some commercialised NOCOLOK® derivates, like NOCOLOK® Li Flux show already reduced solubility when compared to the standard product [1]. While investigating the chemical possibilities for further minimising the residue solubility and the release of F- ions, we have developed NOCOLOK® variants in combination with selected inorganic fluorides.

During this R&D project we also looked closely at the brazing properties of the new fluxes – with a focus on their performance for brazing of aluminium alloys with higher magnesium level. The current maximum magnesium range suitable for CAB with standard NOCOLOK® Flux is approximately 0.3%. Some improvement can be seen when using caesium-containing NOCOLOK® formulations (up to 0.5% Mg) [3] [4]. Some of the new fluxes we developed for further reduced residue solubility surprisingly show higher magnesium tolerance. This article summarizes the results of our laboratory work related to the development of fluxes with further reduced residue fluorides solubility and improved magnesium tolerance.

Basic experimental laboratory procedures

 

1. Lab brazing and alloy specimen setup
For experimental lab furnace brazing we used standard CAB brazing profile and 25 by 25 mm clad sheet coupons (single side) with angle on top. In case of the Mg topic an AMAG (Austria Metal AG) clad alloy (6951/4343) was brazed with an AMAG clad-less angle. Fluxing was done manually (flux load weight on precision scale, drops of isopropanol and homogenous spreading).

Test coupon

2. Solubility data generation
Coupon (3003/4343) with Al angle (Al 99.5%) were manually coated with a dedicated amount of flux blend and brazed as described in point 1. Brazed samples were placed in PET bottles and a defined quantity of demineralised water was added. Daily visual control and air exposure (by opening and closing the lid) was done.

PET-Flasche_klar

To be continued…


  1. P Garcia et al, Solubility Characteristics of Potassium Fluoroaluminate Flux and Residues, 2nd Int. Alum. Congress HVAC&R, Dusseldorf (2011)
  2. P Garcia et al., Solubility and Hydrolysis of Fluoroaluminates in Post-Braze Flux Residue, 13th AFC Holcroft Invitational Aluminum Brazing Seminar, Novi (2008)
  3. J Garcia et al, Brazeability of Aluminium Alloys Containing Magnesium by CAB Process Using Cs Flux, VTMS5, 2001-01-1763 (2001)
  4. H Johannson et al, Controlled Atmosphere Brazing of Heat Treatable Alloys With Cesium Flux, VTMS6 C599/03/2003 (2003)
  5. Handbook of Chemistry and Physics; Ref. BaSO4: 0.0025 g/l
  6. U Seseke, Structure and Effect – Mechanism of Flux Containing Cesium, 2nd Int. Alum. Brazing Con., Düsseldorf (2002)

Brazing of Aluminium Alloys with
Higher Magnesium Content using Non-Corrosive Fluxes – Part 5

Jul 15
2014

Technical Information by Leszek Orman, Hans-Walter Swidersky and Daniel Lauzon

Abstract

For just as long as aluminium has been used for brazing heat exchangers, there has been a trend to down-gauging components for weight savings. The most common alloying element to achieve higher strength alloys for the purpose of down-gauging is magnesium. While magnesium additions are helpful in achieving stronger alloys, the consequence is a decrease in brazeability. This article discusses the mechanism of brazing deterioration with the addition of magnesium and proposes the use of caesium compounds as a way of combating these effects.

We split the article in five parts:

  1. Introduction
  2. Effects of Mg on the Brazing Process
  3. Mechanism of Magnesium Interaction with the Brazing Process
  4. Caesium Fluoroaluminates
  5. NOCOLOK® Cs Flux

NOCOLOK® Cs Flux

As a more practical means of obtaining better brazeability of Mg containing alloys, a mixture of standard NOCOLOK® Flux and caesium fluoroaluminates is used. The positive influence of Cs on brazing magnesium containing alloys was previously reported in a patent for a product where potassium fluoroaluminates were mixed with caesium fluoroaluminates [11]. However, this patent covered a rather wide ratio of potassium fluoroaluminates to caesium fluoroaluminates.

The influence of actual elemental Cs content on brazeability was investigated by Garcia et al [12]. Brazeability was determined by the length of the joint obtained in a system with a gradual increase in gap clearance (similar in concept to the one shown in Fig. 1). In their work they used 6063 alloy with a Mg content of 0.66 wt%. Their major finding is presented in Fig. 6.

fig-6

Fig. 6: Brazeability of AA6063 alloy as a function of caesium content at flux load of 5 g/m2 [12].

As seen in Fig. 5, even a relatively low concentration of Cs in the flux mixture improves brazeability of an alloy containing 0.66 wt% Mg. An increase of Cs concentration above 2 wt% does not lead to further improvement in brazeability. In his work Garcia et al also confirmed that faster heating rates, though positive do not significantly influence brazeability.

This work led to another important finding. By brazing small sample radiators in an industrial type furnace, Garcia et al established a practical threshold for Mg content. The flux containing 2 wt% Cs is effective for brazing aluminium alloys with 0.35% to 0.5 % Mg. At lower levels of magnesium no difference between the standard flux and the 2 wt% Cs flux was observed. Brazing samples containing 0.66% of magnesium yielded leak free parts – but the brazing ratio for fins was not fully satisfactory.

This work led to the standardization of Solvay’s NOCOLOK® Cs Flux at 2 wt% Cs. By using this minimal but effective Cs concentration in the mixture, the chemical and physical characteristics are similar to the standard flux.

Summary

  • Magnesium is very often added to aluminium alloys to increase strength and machinability.
  • The addition of magnesium negatively influences the brazing process due to the formation of smaller fillets and the presence of porosity in the joints. This is due to (a) magnesium diffusing to the surface during the brazing cycle and forming Mg containing oxides which are more difficult to remove by the molten flux and (b) by poisoning the action of flux through the formation of K-Mg-F compounds.
  • The above effect can be made less pronounced when standard NOCOLOK® Flux is mixed with a caesium aluminium fluoride complex. At a concentration of 2 wt% Cs one can observe a positive effect on aluminium alloys containing magnesium. Increasing the Cs content above 2 wt% does not yield any further increase in brazeability.
  • NOCOLOK® Cs Flux works effectively for alloys containing roughly 0.3 to 0.5 wt% Mg. Depending on specific design and process conditions, Cs containing fluxes can also offer benefits for alloys containing 0.3 wt% or even less Mg. For concentrations higher than 0.5 wt% of Mg, the effectiveness of Cs compounds in non-corrosive fluxes gradually decreases.
  • Pure caesium aluminium fluoride complex is effectively used for flame brazing where a lower melting point flux is required.

Download the complete article as a PDF-File.


References:

  1. S. W. Haller, “A new Generation of Heat Exchanger Materials and Products”, 6th International Congress “Aluminum Brazing” Düsseldorf, Germany 2010
  2. R. Woods, “CAB Brazing Metallurgy”, 12th Annual International Invitational Aluminum Brazing Seminar, AFC Holcroft, NOVI, Michigan U.S.A. 2007
  3. T. Stenqvist, K. Lewin, R. Woods “A New Heat-treatable Fin Alloy for Use with Cs-bearing CAB flux” 7th Annual International Invitational Aluminum Brazing Seminar, AFC Holcroft, NOVI, Michigan U.S.A. 2002
  4. R. K. Bolingbroke, A. Gray, D. Lauzon, “Optimisation of Nocolok Brazing Conditions for Higher Strength Brazing Sheet”, SAE Technical Paper 971861, 1997
  5. M. Yamaguchi, H. Kawase and H. Koyama, ‘‘Brazeability of Al-Mg Alloys in Non Corrosive Flux Brazing’’, Furukawa review, No. 12, p. 139 – 144 (1993).
  6. A. Gray, A. Afseth, 2nd International Congress Aluminium Brazing, Düsseldorf, 2002
  7. H. Johansson, T. Stenqvist, H. Swidersky “Controlled Atmosphere Brazing of Heat Treatable Alloys with Cs Flux” VTMS6, Conference Proceedings, 2002
  8. U. Seseke-Koyro ‘‘New Developments in Non-corrosive Fluxes for Innovative Brazing’’, First International Congress Aluminium Brazing, Düsseldorf, Germany, 2000
  9. K. Suzuki, F. Miura, F. Shimizu; United States Patent; Patent Number: 4,689,092; Date of Patent: Aug. 25, 1987
  10. L. Orman, “Basic Metallurgy for Aluminum Brazing”, Materials for EABS & Solvay Fluor GmbH 11th Technical Training Seminar – The Theory and Practice of the Furnace and Flame Brazing of Aluminium, Hannover, 2012
  11. K. Suzuki, F. Miura, F. Shimizu; United States Patent; Patent Number: 4,670,067; Date of Patent: Jun. 2, 1987
  12. J. Garcia, C. Massoulier, and P. Faille, “Brazeability of Aluminum Alloys Containing Magnesium by CAB Process Using Cesium Flux,” SAE Technical Paper 2001-01-1763, 2001

Brazing of Aluminium Alloys with
Higher Magnesium Content using Non-Corrosive Fluxes – Part 4

Jun 24
2014

Technical Information by Leszek Orman, Hans-Walter Swidersky and Daniel Lauzon

Abstract

For just as long as aluminium has been used for brazing heat exchangers, there has been a trend to down-gauging components for weight savings. The most common alloying element to achieve higher strength alloys for the purpose of down-gauging is magnesium. While magnesium additions are helpful in achieving stronger alloys, the consequence is a decrease in brazeability. This article discusses the mechanism of brazing deterioration with the addition of magnesium and proposes the use of caesium compounds as a way of combating these effects.

We split the article in five parts:

  1. Introduction
  2. Effects of Mg on the Brazing Process
  3. Mechanism of Magnesium Interaction with the Brazing Process
  4. Caesium Fluoroaluminates
  5. NOCOLOK® Cs Flux

Caesium Fluoroaluminates

Magnesium is an extremely reactive element and therefore even a small amount of oxygen will cause its oxidation. In standard brazing furnaces most often the level of oxygen in the furnace atmosphere at the temperature ranges below brazing could be relatively high. Thus the formation of magnesium oxides seems to be inevitable. On the other hand, one can think about neutralizing or inhibiting the formation of the poisoning potassium magnesium fluoride compounds mentioned earlier. The formation of those compounds can be reduced in the presence of caesium fluoroaluminate compounds

Caesium fluoroaluminates exist in several compositions and crystallographic states such as CsAlF4, Cs[AlF4 (H2O)2], Cs2AlF5, Cs2AlF5 H2O, Cs3AlF6. The Cs compound commonly used for aluminium brazing contains mainly CsAlF4 and is also known as CsAlF – Complex.

Cs acts as a chemical scavenger for Mg. During the brazing process, caesium reacts with magnesium to form compounds such as CsMgF3 and/or Cs4Mg3F10 [8]. These compounds melt at lower temperatures than the filler metal. As such these compounds do not significantly interfere with aluminium brazing and allow the flux to retain much of its oxide dissolution and wetting capability.

The caesium fluoroaluminate complex has a low melting range (420 – 480°C), a high water solubility (~20 g/l at 20°C), and contains between 54 – 59 % of elemental caesium. Though there are literature references for using the pure Cs-complex as a brazing flux [9], the chemical characteristics present practical problems when one would like to replace standard NOCOLOK® Flux with pure caesium fluoroaluminates complex. The low melting range means that under normal CAB process conditions the flux would essentially dry out by evaporation before reaching the brazing temperature (~ 600oC). Furthermore, the high content of Cs makes it prohibitively expensive as a replacement for standard NOCOLOK® Flux.

However the Cs complex does find a use in several applications such as flame and induction brazing and as a key component of flux paste formulations for specialty alloys. In some processes, mainly flame brazing of copper and aluminium, this complex is the state of the art [10].

Aluminium and copper form a low melting eutectic (546°C). This means that it is not possible to braze copper and aluminium in a CAB process using standard filler metal alloys having a melting range from 577°C to 605°C. It is however possible to join aluminium and copper by flame brazing, but it requires high degree of temperature control and a lower melting filler alloy is recommended. Zinc-aluminium alloys are commonly used for such applications. Lower melting range filler alloys require lower melting range fluxes and since flux consumption for flame brazing is relatively low, it is economically feasible to use a caesium fluoroaluminate complex such as CsAlF4.

Download the complete article as a PDF-File.


References:

  1. S. W. Haller, “A new Generation of Heat Exchanger Materials and Products”, 6th International Congress “Aluminum Brazing” Düsseldorf, Germany 2010
  2. R. Woods, “CAB Brazing Metallurgy”, 12th Annual International Invitational Aluminum Brazing Seminar, AFC Holcroft, NOVI, Michigan U.S.A. 2007
  3. T. Stenqvist, K. Lewin, R. Woods “A New Heat-treatable Fin Alloy for Use with Cs-bearing CAB flux” 7th Annual International Invitational Aluminum Brazing Seminar, AFC Holcroft, NOVI, Michigan U.S.A. 2002
  4. R. K. Bolingbroke, A. Gray, D. Lauzon, “Optimisation of Nocolok Brazing Conditions for Higher Strength Brazing Sheet”, SAE Technical Paper 971861, 1997
  5. M. Yamaguchi, H. Kawase and H. Koyama, ‘‘Brazeability of Al-Mg Alloys in Non Corrosive Flux Brazing’’, Furukawa review, No. 12, p. 139 – 144 (1993).
  6. A. Gray, A. Afseth, 2nd International Congress Aluminium Brazing, Düsseldorf, 2002
  7. H. Johansson, T. Stenqvist, H. Swidersky “Controlled Atmosphere Brazing of Heat Treatable Alloys with Cs Flux” VTMS6, Conference Proceedings, 2002
  8. U. Seseke-Koyro ‘‘New Developments in Non-corrosive Fluxes for Innovative Brazing’’, First International Congress Aluminium Brazing, Düsseldorf, Germany, 2000
  9. K. Suzuki, F. Miura, F. Shimizu; United States Patent; Patent Number: 4,689,092; Date of Patent: Aug. 25, 1987
  10. L. Orman, “Basic Metallurgy for Aluminum Brazing”, Materials for EABS & Solvay Fluor GmbH 11th Technical Training Seminar – The Theory and Practice of the Furnace and Flame Brazing of Aluminium, Hannover, 2012
  11. K. Suzuki, F. Miura, F. Shimizu; United States Patent; Patent Number: 4,670,067; Date of Patent: Jun. 2, 1987
  12. J. Garcia, C. Massoulier, and P. Faille, “Brazeability of Aluminum Alloys Containing Magnesium by CAB Process Using Cesium Flux,” SAE Technical Paper 2001-01-1763, 2001

Brazing of Aluminium Alloys with
Higher Magnesium Content using Non-Corrosive Fluxes – Part 3

May 30
2014

Technical Information by Leszek Orman, Hans-Walter Swidersky and Daniel Lauzon

Abstract

For just as long as aluminium has been used for brazing heat exchangers, there has been a trend to down-gauging components for weight savings. The most common alloying element to achieve higher strength alloys for the purpose of down-gauging is magnesium. While magnesium additions are helpful in achieving stronger alloys, the consequence is a decrease in brazeability. This article discusses the mechanism of brazing deterioration with the addition of magnesium and proposes the use of caesium compounds as a way of combating these effects.

We split the article in five parts:

  1. Introduction
  2. Effects of Mg on the Brazing Process
  3. Mechanism of Magnesium Interaction with the Brazing Process
  4. Caesium Fluoroaluminates
  5. NOCOLOK® Cs Flux

Mechanism of Magnesium Interaction with the Brazing Process

According to M. Yamaguchi et al [5], when magnesium diffuses to the surface during brazing, a chemical reaction takes place with the flux resulting in the generation of KMgF3.

The authors suggest the following equations to explain some of the chemical interactions between magnesium and K1-3AlF4-6 flux:

  • 3 MgO + 2 KAlF4  →  MgF2 + 2 KMgF3 + Al2O3  (a)
  • 3 MgO + 2 KAlF4  →  2 MgF2 + K2MgF4 + Al2O3  (b)
  • 3 MgO + 2 K3AlF6 > →  3 K2MgF4 + Al2O3  (3)

By performing XRD (X-ray Diffraction) phase identification on products brazed with Mg containing alloys, A. Gray et al [6] confirmed the presence of K2MgF4, spinel oxide (Al2MgO4) and possibly KMgF3. These magnesium containing compounds have a characteristic needle like morphology as shown in Fig. 5.

fig-5

Fig. 5: Morphology of magnesium containing compounds as seen by Scanning Electron Microscope [6].

H. Johansson et al [7] also determined that at temperatures above 425°C the magnesium diffusion to the surface is very rapid resulting in the formation of magnesium oxide (MgO) and spinel oxides (Al2MgO4). These oxides have very low solubility in NOCOLOK® Flux. Subsequently these magnesium oxides react with the flux resulting in the formation of magnesium fluoride (MgF2) and potassium magnesium fluorides (KMgF3, K2MgF4, see equations a), b), and c)). These reactions change the flux chemical composition causing its melting range to rise. The melting point of these magnesium fluorides is very high, which in turn drives the melting point of the flux upwards, thereby decreasing the activity of the flux. The above factors also cause a decrease in the flowing characteristics of the flux thus lowering its overall effectiveness. Therefore the desired key point to limit the flux poisoning effect would be to reduce the formation of magnesium oxides and potassium magnesium fluorides.

Download the complete article as a PDF-File.


References:

  1. S. W. Haller, “A new Generation of Heat Exchanger Materials and Products”, 6th International Congress “Aluminum Brazing” Düsseldorf, Germany 2010
  2. R. Woods, “CAB Brazing Metallurgy”, 12th Annual International Invitational Aluminum Brazing Seminar, AFC Holcroft, NOVI, Michigan U.S.A. 2007
  3. T. Stenqvist, K. Lewin, R. Woods “A New Heat-treatable Fin Alloy for Use with Cs-bearing CAB flux” 7th Annual International Invitational Aluminum Brazing Seminar, AFC Holcroft, NOVI, Michigan U.S.A. 2002
  4. R. K. Bolingbroke, A. Gray, D. Lauzon, “Optimisation of Nocolok Brazing Conditions for Higher Strength Brazing Sheet”, SAE Technical Paper 971861, 1997
  5. M. Yamaguchi, H. Kawase and H. Koyama, ‘‘Brazeability of Al-Mg Alloys in Non Corrosive Flux Brazing’’, Furukawa review, No. 12, p. 139 – 144 (1993).
  6. A. Gray, A. Afseth, 2nd International Congress Aluminium Brazing, Düsseldorf, 2002
  7. H. Johansson, T. Stenqvist, H. Swidersky “Controlled Atmosphere Brazing of Heat Treatable Alloys with Cs Flux” VTMS6, Conference Proceedings, 2002
  8. U. Seseke-Koyro ‘‘New Developments in Non-corrosive Fluxes for Innovative Brazing’’, First International Congress Aluminium Brazing, Düsseldorf, Germany, 2000
  9. K. Suzuki, F. Miura, F. Shimizu; United States Patent; Patent Number: 4,689,092; Date of Patent: Aug. 25, 1987
  10. L. Orman, “Basic Metallurgy for Aluminum Brazing”, Materials for EABS & Solvay Fluor GmbH 11th Technical Training Seminar – The Theory and Practice of the Furnace and Flame Brazing of Aluminium, Hannover, 2012
  11. K. Suzuki, F. Miura, F. Shimizu; United States Patent; Patent Number: 4,670,067; Date of Patent: Jun. 2, 1987
  12. J. Garcia, C. Massoulier, and P. Faille, “Brazeability of Aluminum Alloys Containing Magnesium by CAB Process Using Cesium Flux,” SAE Technical Paper 2001-01-1763, 2001

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