RU2263568C2 - Paste for soldering aluminum and its alloys - Google Patents

Abstract

FIELD: high-temperature soldering articles such as units of wave-guide equipment of aluminum and its alloys by dipping to melt salts.

SUBSTANCE: paste on base of powder solder of aluminum-silicon system with particle size 100-200 micrometers includes solution of high-molecular compound in isoamyl acetate as organic binder. Paste also contains finely divided powder of aluminum with particle size equal to 20 micrometers or less and(or) pigment aluminum dust. Paste includes next relation of components, mass %: organic binder, 24 - 28; finely divided aluminum powder, 10 - 40; powder solder of aluminum-silicon (eutectics) system, the balance.

EFFECT: enhanced quality of soldered joints due to stable composition and adhesion properties of paste, lowered cost and toxicity of paste.

2 cl, 1 dwg, 2 tbl, 7 ex

Description

The invention relates to brazing, in particular to pastes for high-temperature (BT) brazing of aluminum and its alloys by immersion in molten salts.

Known paste for brazing aluminum and its alloys (hereinafter referred to as aluminum) by immersion in molten salts, which includes powdered solder of the Al-Si system (hereinafter powder solder), AlF ₃ salt, a binder - water [1].

The use of water as a binder leads to:

firstly, the low adhesion strength of the powder solder to the brazed surface,

secondly, to the oxidation of powdered solder during the preheating of soldered parts before immersion in molten salts.

This reduces the quality of soldered joints.

Known paste for brazing aluminum, which contains, wt.%:

Al-S ₁ powder solder 70.1-80 with a particle size of 100-200 microns. ethyl alcohol or isopropyl alcohol 18-25 shellac 1-4 potassium fluorozirconate or potassium fluorotitanate 0.1-0.9

(2 - prototype).

The advantage of this paste is that an alcohol-shellac mixture is used as an organic binder (ligament).

But,

firstly, the paste has an unstable composition over time due to the evaporation of alcohol from the organic binder, as a result, the binder thickens, which complicates the use of the paste;

secondly, the remains of shellac do not completely burn out during preheating of parts, they are carbonized, forming a carbonaceous gray coating, which impairs the adhesive properties of the paste and thereby reduces the wettability and spreadability of the powder solder;

thirdly, the adhesion of the paste to the brazed surface after preheating in air is low and when parts are transferred to the bath, part of the powdered solder is scattered over its surface and washed off with a molten salt during immersion even before it is melted, as a result, the quality of the solder deteriorates, nepropagation appears;

fourthly, one should also take into account the relative scarcity and high cost of imported shellac, which complicates its use.

The technical result of the invention is to increase the stability of the composition of the paste over time, increase its adhesive properties and, consequently, increase the quality of soldered joints, as well as reduce its cost and toxicity.

The technical result is achieved by the fact that in the known paste for brazing aluminum and its alloys by immersion in molten salts containing a powdery solder of the aluminum-silicon system with a particle size of 100-200 μm and an organic binder, a solution of a high molecular weight compound in isoamyl acetate is used as an organic binder, paste additionally contains finely divided aluminum powder with a particle size equal to or less than 20 microns and / or pigmented aluminum powder in the following ratio of components, wt.%:

high molecular weight solution 24-28 compounds in isoamyl acetate (10%) fine aluminum powder and / or pigmented aluminum powder 10-40 powder solder system aluminum - silicon (eutectic) rest

The high molecular weight compound is a copolymer of isobutyl methacrylate with methacrylic or acrylic acid.

Use as an organic binder of a 10% solution of high molecular weight (BM) compound, in particular, a copolymer of isobutyl methacrylate with methacrylic or acrylic acid (SPIBM) in isoamyl acetate, which

firstly, due to the ability to maintain its viscosity unchanged for a long time (1 year or more), the paste will provide stability to the composition over time;

secondly, due to the fact that the VM solution of the compound has adhesive properties, it provides these properties to the paste and thereby increase its adhesive properties;

thirdly, due to the ability to completely decompose at temperatures above 500 ° C - preheating temperature - the organic binder does not leave carbon gray deposits on the soldered surface and thereby improve the quality of the soldered joints;

fourthly, it reduces the cost of paste, since the components of the organic binder are produced by domestic industry.

The introduction into the paste of aluminum powder with a particle size equal to or less than 20 microns and / or pigmented aluminum powder will improve the adhesive properties of the paste, and especially at the stage of preheating.

The proposed paste is not toxic, as excluded from the paste fluoride salts used in the prototype.

The invention is illustrated by the photograph, which depicts a typical node waveguide technology: waveguide - flange and waveguide wiring, soldered by the proposed paste.

Example 1

The solder paste is prepared as follows.

Powder solder of the AI-Si system (eutectic) with a particle size of 100-200 microns of grade AKD - 12-3 (TU6 - 02-007-75) and pigment aluminum powder PAP - 2 (GOST 5494 - 74) are poured into a porcelain cup; mix, then an organic binder is introduced into the mixture - a 10% solution of SPIBM-01-N (TU6 - 01-2-744-85) in isoamyl acetate (TU6 - 09-2-1240-76) and mix again until a homogeneous mass is formed - pasta.

Examples 2-5.

Analogously to example 1, pastes were prepared, but having different quantitative proportions of the components, both indicated in the claims (examples 2-3), and beyond it (examples 4-5), except for the values of the amount of pigmented aluminum powder, which are taken as average.

Examples 6-7.

Analogously to example 1, pastes were prepared, but having an average value of the amount of organic binder, and the amount of pigmented aluminum powder, beyond the limits specified in the claims.

Examples 1a-7a.

Similarly to examples 1-7, respectively, pastes were prepared, but with fine aluminum powder instead of pigmented aluminum powder.

From the prepared compositions, the pastes were made by extruding tablets through a stencil with a diameter of 5 mm and a thickness of 3 mm, which were used to determine the adhesion force of the tablet — the adhesion of the paste — to the surface of samples made of aluminum alloy AMts of size 20 × 15 × 2, after preliminary heating.

AMts alloy samples are made by milling followed by degreasing in acetone.

Heating is carried out in a muffle furnace in an air atmosphere according to the regime:

- temperature - 530 ° C

- excerpt - 10 minutes

After sintering, a visual analysis of the samples was carried out and the adhesion strength was determined.

All data are summarized in tables 1 and 2.

As can be seen from the tables:

The adhesion force of the tablets from the prepared paste compositions to the surface of samples from Amz — the adhesion of the paste — is on average 65 GS containing aluminum pigment powder (examples 1-3) and 40 GS containing finely divided aluminum powder (examples 1a-3a) with the ratio of the components of the paste specified in the claims, which is more than 10 times the adhesion force, with a ratio of components that go beyond the limits specified in the claims (examples 4-7) and (examples 4a-7a), as well as in comparison with the prototype (example 8).

All samples lacked a gray coating, except for the prototype sample (example 8). This confirms that the organic binder has completely decomposed into gaseous components.

The prepared paste (examples 1-3) and (examples 1a-3a) was also used for soldering typical nodes of the waveguide technique:

waveguide - flange and waveguide wiring made of aluminum alloy AMts.

The paste is applied with a rubber spatula 3-4 mm thick around the perimeter of the waveguides.

Soldering was carried out according to the mode:

preheating 530 ° C in an air atmosphere furnace holding time 10 minutes immersion in molten flux 16 VK at temperature 620 ° C molten salt holding time 30 sec

A visual analysis of the soldered seam was performed.

Along the entire perimeter of the soldered seam of all waveguide nodes (examples 1-3) and (examples 1a-3a), continuous uniform fillets are observed.

Thus, the proposed paste for brazing aluminum and its alloys by immersion in molten salts has a high stability of the composition and high adhesive properties and thereby provides an increase in the quality of soldered joints.

The proposed pasta is cheap due to the exclusion of scarce and expensive shellac, a natural resin sourced from India.

The proposed paste is non-toxic due to the exclusion of fluoride salts.

Information sources

1. Swiss patent No. 410592, cl. 49, B 23 K 31/01.

2. USSR author's certificate No. 493319 priority 07.05.73, 23 K 35/36, publ. bull. No. 44, 1975

table 2 No. p / p The composition of the paste, wt.% Research results Organic binders Fine aluminum powder Powder solder (eutectic) Adhesion after sintering HS * Visual on preserving the geometry (shape) of the tablet and the presence of gray plaque Visual on the quality of the fillet of the perimeter of the solder seam of the waveguide nodes 1a 26 25 49 40 The tablet retains its shape, gray plaque is absent Continuous, uniform fillets around the perimeter 2a 24 25 51 40 Same Same Per 28 25 47 40 Same Same 4a nineteen 25 56 4 The tablet loses its shape, no gray coating Did not 5a 33 25 42 5 Same Did not 6a 26 5 69 5 Same Did not 7a 26 45 29th 4 Same Did not * Average value of 3 measurements

Claims (2)

1. Paste for brazing aluminum and its alloys by immersion in molten salts, containing a powder solder of the aluminum-silicon system and an organic binder, characterized in that a powder solder with a particle size of 100-200 μm is used, a 10% solution is used as an organic binder high molecular weight compounds in isoamyl acetate, while the paste further comprises a finely divided aluminum powder with a particle size equal to or less than 20 μm and / or pigmented aluminum powder in the following ratio ENTOV, wt.%: 10% High Molecular Compound Solution in isoamyl acetate 24-28 Fine aluminum powder and / or pigmented aluminum powder 10-40 Powder Solder System aluminum silicon Rest 2. The paste according to claim 1, characterized in that a copolymer of isobutyl methacrylate with methacrylic or acrylic acid is used as a high molecular weight compound.