RU2280548C1 - Flux for low temperature soldering of aluminum and its alloys - Google Patents

Abstract

FIELD: fluxes for soldering aluminum and its alloys.

SUBSTANCE: flux may be used as filler in tubular low melting lead-tin solders of given kinds. Flux contains, mass %: triethanolamine, 43 - 75; ammonium bifluoride, 25 - 50; acetamide, 0 - 7. Flux provides low temperature of aluminum surface activation in range 250 - 300°C, good spreadability of solder.

EFFECT: improved properties of flux, enhanced efficiency of soldering with use of such flux.

1 tbl, 5 ex

Description

The invention relates to fluxes for brazing aluminum and its alloys with low-temperature solders.

Known flux compositions for brazing aluminum / 1 /, containing triethanolamine with the addition of salts of fluoroborates of zinc, cadmium, ammonium.

The disadvantage of the described fluxes is that this flux for brazing the surface of aluminum and aluminum alloys requires a temperature of 320-370 ° C for the activation of salts.

The closest of this series in technical essence is taken as a prototype flux / 2 /, which consists in the fact that it contains triethanolamine and 10-15% zinc tetrafluoroborate.

The disadvantage of this flux is the lack of activation of the aluminum surface at a melting point of solder 250-300 ° C. The flux provides surface activation at a temperature of 320-370 ° C during the decomposition of zinc terafluoroborate, which leads to blackening of the soldering site due to carbonization of triethanolamine.

The aim of this invention is to provide a flux with a low activation temperature of the aluminum surface for use as a flux filler in tubular low-melting lead-tin solders of the type POSSU 30-0.5 or POSSU 18-0.5.

The goal is solved in that the flux containing triethanolamine, still contains as an activator ammonium bifluoride and a thickener - acetamide, in the following ratio of components, wt%: triethanolamine - 43-75; ammonium bifluoride - 25-50; acetamide - 0-7.

A common feature of the proposed composition of the flux and flux of the prototype is the use of triethanolamine bases.

A distinctive feature of the proposed flux is that it contains ammonium bifluoride and a thickener, acetamide, as an activator.

These differences allow you to activate the surface of aluminum at the time of melting of lead-tin solder at a temperature of 250-300 ° C. The flux is a mixture of triethanolamine, an activator of ammonium bifluoride and a thickener - acetamide. With a decrease in the content of ammonium bifluoride less than 25%, the flux activity decreases, it requires an increase in its consumption and the residues of carbonization of triethanolamine increase, and the quality of soldering decreases.

With an increase in the content of ammonium bifluoride by more than 50%, the wettability of the surface decreases, the solder collects in balls, does not spread sufficiently on the surface and it is necessary to increase the consumption of material, while the quality of the solder in appearance decreases. In the absence of a binder, acetamide, the flux is a liquid mass and can be used by brushing on a brazed surface. When using such a flux in a tubular solder, there is a leakage of flux from the tube during storage and incomplete soldering of products during subsequent use. When the acetamide content in the flux is more than 8%, the flux at room temperature takes on a crystalline structure and the tube with the internal flux-filler breaks when bent, which increases the consumption in the form of waste.

An unexpected effect of the ratio of components was manifested in the fact that ammonium bifluoride, when heated with triethanolamine, neutralizes its OH group with the formation of ethanolamine fluorohydrate. When a neutral or acidic environment appears (with an excessive dosage of ammonium bifluoride), flux reduces the wettability and spreadability of the solder. During heating to a temperature of 300 ° C, the place of soldering of the aluminum surface, the flux liquefies, spreads over the brazed aluminum surface, activates it by dissolving the oxides, and the molten solder spreads over the surface. At 360 ° C, the components of the flux mostly evaporate.

The flux of the specified composition is applicable for soldering aluminum or aluminum alloys, such as Mg-Al alloys, with low-temperature solders of the type POSSU 18 or POSSU 30-0.5.

The following examples illustrate the invention in more detail.

Example. The flux was prepared from a mixture of 73 g of triethanolamine by heating to 120 ° C with the addition of 25 g of ammonium bifluoride and 2 g of acetamide. An aluminum plate weighing 1 g was heated to 270 ° C, a cylinder of 0.3 g solder POSSu 30-0.5 and 0.1 g flux was placed. After warming up the plate to 300 ° C for 3 min, the plate was washed from flux residues, weighed, and the solder spreading area was measured on a millimeter grid. The area of the soldering spot referred to the sample is 2.2 mm ² / g. Spot soldering sample with flux according to the prototype of 0.5 mm ² / g

Examples are given in table form.

Components% / No Experience No. 1 Number 2 Number 3 Number 4 Number 5 triethanolamine 61 43 73 84 35 Ammonium bifluoride 35 fifty 25 fifteen 65 acetamide four 7 2 one 0 Spreading mm ² / g 2.2 2.6 1,1 0.6 0.8 In example No. 4 shown in the table, the place of soldering is thickened and of a smaller area than No. 1-3.
In example No. 5, the place of soldering in the form of 4 separate rations.

The proposed flux provides an increase in the wetting of POSSu 30-0.5 solder on the aluminum surface and can be used as a filler.

Sources of information taken into account.

1. Khryapin V.E. Handbook soldering iron. M .: Mechanical Engineering, 1981, p. 106.

2. Auto USSR No. 944845, M.cl. At 23 k 35/362.

Claims (1)

Flux for low-temperature brazing of aluminum and its alloys, containing triethanolamine and an activator, characterized in that it contains a thickener - acetamide, and as an activator - ammonium bifluoride, in the following ratio, wt.%: Triethanolamine 43-75 Ammonium bifluoride 25-50 Acetamide 0-7