Process for brazing of aluminum alloys and a flux

Abstract

A process for brazing of aluminium magnesium alloys is described applying a flux which comprises KAlF.sub.4 or CsAlF.sub.4 or both as major constituent. The flux further comprises at least one alkaline or alkaline earth metal compound selected from the group consisting of KAlF.sub.4, CsAlF.sub.4, Li.sub.3AlF.sub.6, CaF.sub.2, CaCO.sub.3, MgF.sub.2, MgCO.sub.3, SrF.sub.2, SrCO.sub.3, BaF.sub.2, and BaCO.sub.3. Preferably the flux comprises or consists of KAlF.sub.4, CsAlF.sub.4, and Li.sub.3AlF.sub.6 and optionally contains also BaF.sub.2.

Claims

1. A process for brazing parts of aluminum alloy comprising equal to or more than 0.5 by weight of magnesium in the interface, the process comprising a step of applying a brazing flux to at least one of the parts to be joined, a step of assembling the parts to be joined and a step of heating the parts to be joined to a temperature of equal to or higher than 450 C. to provide brazed joint parts, wherein the brazing flux comprises equal to or more than 80% by weight, relative to the total weight of the brazing flux, of a first component and equal to or more than 3% by weight of a second component, relative to the total weight of the brazing flux, wherein the first component is a monoalkali tetrafluoroaluminate selected from the group consisting of KAlF.sub.4, CsAlF.sub.4 and mixtures thereof, and the second component is at least one alkaline or alkaline earth metal compound selected from the group consisting of KAlF.sub.4, CsAlF.sub.4, Li.sub.3AlF.sub.6, CaF.sub.2, CaCO.sub.3, MgF.sub.2, MgCO.sub.3, SrF.sub.2, SrCO.sub.3, BaF.sub.2, BaCO.sub.3, and mixtures of two or more thereof, wherein the first component and the second component are not identical, and wherein a content of free KF is lower than 0.1% by weight, relative to the total weight of the brazing flux if at least one compound selected from the group consisting of LiF, NaF and CaF.sub.2 is comprised in the flux.

2. The process of claim 1 wherein the first component is KAlF.sub.4.

3. The process of claim 1 wherein the second component is selected from the group consisting of Li.sub.3AlF.sub.6, CsAlF.sub.4, CaF.sub.2, MgF.sub.2, SrF.sub.2, BaF.sub.2, and mixtures of two or more thereof.

4. The process of claim 1 wherein the second component is selected from the group consisting of Li.sub.3AlF.sub.6, CsAlF.sub.4, BaF.sub.2, and mixtures of 2 thereof, or mixtures of Li.sub.3AlF.sub.6, CsAlF.sub.4 and BaF.sub.2.

5. The process of claim 1 wherein the first component is KAlF.sub.4 in an amount of equal to or greater than 80% by weight relative to the total weight of the brazing flux, and the second component is present in an amount of equal to or greater than 5% by weight, relative to the total weight of the brazing flux, and is selected from the group consisting of Li.sub.3AlF.sub.6, CsAlF.sub.4, BaF.sub.2, and mixtures of two or more thereof.

6. The process of claim 1 wherein additionally a brazing additive is applied.

7. The process of claim 1 wherein parts with a magnesium content of at least 0.6% by weight at the interface are brazed.

8. The process of claim 1 wherein parts of heat exchangers are brazed.

Description

EXAMPLES

General Remarks

(1) Used Aluminum Parts:

(2) a) Commercially available AMAG 6951 brazing sheet (0.68% Mg, 4343 clad) and clad-less AMAG angle material (0.68% Mg) from Austria Metal AG were used. The Mg content in the metal-to-metal interface adds up to 1.36% by weight Mg (20.68%) in total. b) Commercially available AMAG 6951 brazing sheet (0.68% Mg, 4343 clad) and clad-less AMAG AA1050 (Al 99.5%) angle from Austria Metal AG were used. The Mg content in the metal-to-metal interface adds up to 0.68% by weight Mg (0.68+0%) in total.
Brazing Process:

(3) Brazing was performed according to a standard CAB brazing profile and 25 by 25 mm clad sheet coupons (single side) with angle on top. Fluxing was done manually (flux load weight on precision scale, drops of isopropanol and homogenous spreading). Each test was performed 3 times.

(4) Evaluation of Joints:

(5) After brazing, the angle was removed by pulling, and the interface section was analyzed by Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM/EDX) Spectroscopy.

Example 1

AMAG 6951 Brazing Sheet (0.68% Mg, 4343 Clad) and Clad-Less AMAG Angle Material (0.68% Mg)

(6) The flux load in examples 1.X was always 10 g/m.sup.2.

Example 1.1 (Comparison)

Brazing with NocolokCs

(7) NocolokCs was used as flux. SEM/EDX showed a very thin seam with a low and in part no meniscus.

Example 1.2

Brazing with KAlF4 and BaF2

(8) A mixture of KAlF.sub.4 (90% by weight) and BaF.sub.2 (10% by weight) was used as flux. SEM/EDX showed a very thin seam with a small meniscus.

(9) Accordingly, the joint was slightly better with this flux.

Example 1.3

Brazing with KAlF4/CsAlF4/Li3AlF6

(10) A mixture of KAlF.sub.4 (94% by weight), CsAlF.sub.4 (2% by weight) and Li.sub.3AlF.sub.6 (4% by weight) was used as a flux. The brazing was performed 3 times. Two times, a good brazing result was achieved.

Example 1.4

Brazing with KAlF4/CsAlF4/Li3AlF6

(11) A mixture of KAlF.sub.4 (93% by weight), CsAlF.sub.4 (4% by weight) and Li.sub.3AlF.sub.6 (3% by weight) was used as a flux. The brazing was performed 3 times. The seam was thin, the meniscus was small.

Examples 2.X

The Flux Load in Examples 1.X was Always 15 g/m2

(12) Examples 1.1 to 1.4 were repeated, but with said 15 g/m.sup.2 flux load.

(13) All specimens showed a small meniscus. Examples 2.2 to 2.4 (according to the invention) always showed a better brazing result than comparison example 2.1.

Example 3

Brazing with AMAG 6951 Brazing Sheet (0.68% Mg, 4343 Clad) and Clad-Less AMAG AA1050 (Al 99.5%) Angle

(14) The flux load always was 5 g/m.sup.2.

Example 3.1 (Comparison)

Brazing with NocolokCs

(15) Brazing was performed using NocolokCs. After brazing, a partial thin meniscus was observed.

Example 3.2

Brazing with KAlF4, CsAlF4 and Li3AlF6 (4% by Weight)

(16) A mixture of KAlF.sub.4 (94% by weight), CsAlF.sub.4 (2% by weight) and Li.sub.3AlF.sub.6 (4% by weight) was used as a flux. The brazing was performed 3 times. All three times, a well-developed meniscus was observed.

(17) The examples above demonstrate that the fluxes according to the invention are superior to NocolokCs, a flux recommended for brazing of AlMg alloys, and which comprises approximately 79% by weight of KAlF.sub.4, approximately 19% by weight of K.sub.2AlF.sub.5 or its hydrates, and approximately 2% by weight of CsAlF.sub.4.

Example 4

Flame Brazing

(18) A brazing sheet and an angle, both from AlMg alloy with 0.75% by weight of Mg, clad with AlSi12 alloy, are assembled and heated with a torch flame until flux and then the cladding melts to provide a brazed assembly.