DE2326360A1 - SOLDERABLE ALUMINUM-MAGNESIUM-SILICON ALLOY - Google Patents

Description

Priority: May 23, 1972, France, No. 72 18,339

Solderable aluminum-magnesium-silicon alloy

The invention relates to aluminum alloys containing magnesium and silicon, the composition of which is specifically geared towards the large-scale production of soldered parts, that are resistant to corrosion and erosion by water. The invention also relates to a method for the production of soldered connections using these aluminum-based alloys and the use of these soldered Alloy parts for elements used in the manufacture of heat exchangers be applied.

It is already known to use aluminum-silicon alloys to solder alloys of aluminum that contain manganese (alloy 3003) or manganese and magnesium (such as alloy 3004) or magnesium and silicon with a copper content of more than 0.15 % (such as 6951) or magnesium and silicon with a manganese content of about 0.60 % (FR-PS 1 131 373). (The number designation of the alloys used in this description corresponds to the proposals of "Aluminum Standard 'and data" of the Aluminum Association, USA).

309849/0560

However, none of these light alloys intended for brazing are perfectly suited for making a large one Series of heat exchanger elements which, in addition to improved mechanical properties, have good resistance to Must show corrosion by the circulating liquid, v / ie water or oil or mixtures of water and organic or inorganic products that act as anti-gelling agents and / or anti-corrosion agents.

The realization of heat exchangers using lighter Aluminum alloys under good economic and technical conditions have numerous practical requirements: So the soldering must be carried out in large series, what the Use of a base alloy, the combustion temperature of which is high enough to carry out the To enable soldering in the oven and as far as possible from the temperature of the soldering. The base or substrate alloy must be easily applied in the form of sheet metal, thin strips, drawn or cast and electro-welded pipes can be. The solder joint must be easy to form and must exhibit good mechanical strength. The thermal Properties of the base alloy must have an effective heat exchange between the fluid cooling medium and the air enable. After all, they have to. soldered elements and devices excellent resistance to the Have corrosion and erosion due to the fluid cooling medium that is circulated in the exchanger.

In addition to the known alloys given above, sometimes If one or more of the listed conditions were satisfied, they did not, however, meet all of these conditions. For example, alloys 3003 and 3004 have rather poor mechanical strength after brazing and a limited corrosion resistance to water. The aluminum-magnesium-silicon alloys of type 6951, which contain copper, show the same disadvantage with regard to the Corrosion; the aluminum-magnesium-silicon alloys, the contain more than 30 ^ manganese, show under certain conditions

309849/0560

Depending on the composition and the thermal treatment in the presence of the cooling water of an exchanger, the tendency to corrode due to pitting. Finally, the aluminum-magnesium (about 0.67-0.69 %) alloys containing silicon show a combustion temperature that decreases when the silicon content exceeds 0.50%. Carried out by the applicant. Experiments have in fact shown that this temperature falls from a value of 618 ° C at 0.35 to 0.40% Si 611 ⁰ C at 0.52% of Si, if the content of Mg in both cases, a constant between 0 , 67 and 0.69 % .

It has now been found that the difficult problem, one to be soldered To create an alloy that meets all the essential requirements to be met, can be solved, by precisely determining the proportions of metals and impurities in an aluminum-magnesium-silicon alloy and at the same time the conditions of the metallurgical process are set, which is used for the production of brazed elements is used for heat exchangers.

The invention therefore relates to a solderable alloy based on aluminum, magnesium and silicon, which is characterized by this is that the content of magnesium and silicon is within the following narrow limits and that the proportions of Impurities, especially copper, lower than the following Values are.

The composition of this alloy is within the following Limits:

(I) Magnesium 0.20 to 0.70 % Silicon 0.30 to 0.50 Jo impurities ^. 0.80 % aluminum. Rest to 100 %,
where the impurities iron 4-0.25 / j,

Copper <: 0.05

So,

Zinc ^ 0.20 % and manganese 4 0.15 #.

According to a special advantageous embodiment of the invention the alloy has the following composition:

309849/0560

(II) Magnesium 0.45 to 0.65 %

Silicon 0.35 to 0.47 %

Impurities ^ - 0.50 %,

. = where iron - ^ 0.23 %,

Copper ^ - 0.02 %,

Zinc "^ .0.10 #,

Manganese '""<: 0.08 % ,

Aluminum, rest to 100 #

According to a further embodiment of the invention, the alloy defined above can contain a small proportion of foreign elements, which can be one of the elements beryllium (up to 100 parts per million parts) and lanthanides or rare earth metals (up to 0.5%) .

The alloys according to the invention of the composition I and especially of the composition II are very particularly suitable for use for soldering processes in a tunnel furnace in air or under a regulated atmosphere or also for soldering under a vacuum. They can withstand treatment temperatures up to 620 ° C, while the aforementioned known alloys show combustion temperatures several degrees below this temperature. As is shown in the example below, their excellent mechanical properties are not impaired by the metallurgical process that takes place during the soldering process, namely by heating to a temperature of 600 to 620 ^° C., rapid cooling under a gas flow (which makes the connection of the assembly Base alloy and solder alloy guaranteed simultaneously with the metallurgical hardening process) and subsequent treatment at a temperature of 150 to 245 ⁰ C, which corresponds to a tempering process for hardening.

In this context, it was found that the Temperungs- or tempering treatment, which is preferably carried out from 220 to 240 ⁰ C for 10 to 60 JMinuten, in particular for 15 to 30 minutes, "in two respects is valuable" because the production of a quantity of brazed composite parts through a continuous unification process

309849/0560

gear facilitates and enables corrosion resistance of the soldered material to an optimal value with respect to water, such as the results of the one below Show corrosion tests described in the example.

The use of the alloys according to the invention for production of parts soldered in large series can be carried out according to known methods and do not require any special ones Precautions.

The brazing alloy can consist of a classic aluminum-silicon alloy, which comprises 7 to 13% Si and can also contain any additional element that enables the formation of the soldered joint by modifying the viscosity, reducing the interfacial tension and lowering the melting point of the solder facilitates or increases the resistance of the solder to oxidation. Such elements include, for example, elements such as alkali metals or alkaline earth metals or boron in Mcagen from 0.005 to 3 %, copper in amounts from 0.1 to 10 %, zinc in amounts from 0.1 to 12 %, magnesium in amounts from 0, 01 to 10 %, indium, rare earth metals in amounts of 0.01 to 1 %, and the like.

The connection between the solder and the base or substrate alloy according to the invention may by already known methods durch.Plattierung in the heat or under Raumtempera_ door rollers in the heat (350 to 500 ⁰ C) and then optionally carried out in the cold.

The solder can be arranged around a core made of the type I alloy or, on the contrary, can be provided in the form of a central layer between two layers made of the alloy I. It is also possible to alternate several layers of the solder alloy with layers of alloy I, the solder layers generally accounting for 1 to 20% of the thickness of each layer of the base or sub-base alloy.

Finally, according to a variant, it is possible »plated To form composite structures that consist of the following components

3a9849 / 0560

len consist: a layer of a soldering alloy - an intermediate layer of an alloy according to the invention, which, however, is practically free of magnesium (less than 0.1 %) - a layer of alloy I. In this way, any local reduction in the melting temperature of alloy I by enrichment of silicon above a content of 0.50 % must be avoided.

The manufacture of the heat exchanger elements itself from the above-described clad alloys can by known methods of deep drawing or pressing and bending (for sheet metal and strips), by known processes of rolling-welding and subsequent stretching or drawing and calibration (for parts in the form of tubes) are also carried out.

The following example illustrates the characteristic properties of an alloy according to the invention by it is the metallurgical process used from the moment of brazing and the excellent properties of the obtained soldered elements illustrated, in particular with regard to the corrosion and erosion resistance a cooling liquid of a heat exchanger.

example

An alloy according to the invention intended for soldering and having the following composition was used as the starting material:

Magnesium 0.60 %

Silicon 0.40 %

Impurities: iron 0.2 %, copper 0.02 %,

other < 0.2056 aluminum: supplement to 100 %

An aluminum alloy with 10 ^. Silicon and Oj, 4 % iron used.,

1-3 semi-continuously 300 χ 1100 mm plates of solderable alloy were cast, with a homogenizing treatment for 8 hours at 580 ° C and a peeling treatment

309849/0560

treatment to a thickness of 285 mm. A part of these plates was ^{hot rolled at 500 °} C. to a thickness of 4 mm and then cold rolled until the desired end thickness was achieved, while another part was clad by lamination with the help of the solder alloy - which was previously applied hot was - whereby a material was obtained. which was plated on 10% per area by means of the solder. The processing of the clad blanks was carried out to the final thickness, using the same procedure as for salting the unclad sheets.

After the mechanical deformation of the materials into heat exchanger elements, As explained above, these were placed on a suitable jig subjected to the following treatments:

Immersion in an aqueous bath containing a suitable flux for soldering (alkali chlorides, zinc chloride, sodium sulfate luoride, aluminum fluoride),

Introduction into a soldering furnace with ventilation, a temperature of 610 to 620 ⁰ C,

rapid cooling with the aid of air at a cooling rate in the order of 1 ° C / second,

Rinse with water,

Drying treatment and tempering or tempering treatment under the following conditions;

Heating to 240 ^° C. for 12 to 15 minutes, holding at 240 ^° C. for 20 minutes.

The characteristic properties of the alloy according to the invention were then measured on samples of the indicated Type I substrate alloy, which correspond to the metallurgical Treatments had been subjected.

a) Mechanical properties.

The mechanical properties are summarized in Table 1 below. In this table, R 0.2 means the.

309849/0560

Breaking load at 0.2 % and Rm the maximum breaking load.

Table 1

Treatment - R 0.2p Rm ₂ stretch

of the sample kg / now .kg / mm %

Annealed (recuit) 3.7 8.3 40

hardened (trempe-müri) 7.1 16.6 24.2

annealed (income) 15.3 18.7 13.7

The annealing of the sample corresponds to a one-hour treatment at 400 ⁰ C and subsequent cooling with a rate of 30 ° C / hour.

Curing \ vurde by the following treatment obtained: immersion in the above aqueous Flußmittelbe.d for 10 minutes at 570 ^u C and then 5 minutes at 600 ⁰ C, followed by hardening by cooling with air at a rate of 1 ° C / second, and Rinsing with boiling water for 10 minutes, followed by long aging (15 days) at room temperature. For tempering, the following treatments are carried out: Hardening treatment and subsequent hardening tempering, which is described above, for 20 minutes at 240 ^° C. The sample treated in this way therefore corresponds practically to the state in which the alloy according to the invention is after it Process steps described above: brazing in the oven - cooling in the air - rinsing - drying.

It can therefore be seen that the alloy according to the invention in the annealed state, because of its high elongation, is well suited to being deformed before your soldering and that after exhibits very satisfactory mechanical properties after tempering.

309849/0560

ΐ ») Corrosion behavior in the presence of water.

The corrosion was examined on 1 mm thick plates made from the alloy according to the example, all of which above the treatments described. In comparison for this purpose, the same plates made of two known alloys are subjected to the same treatments. The known The alloys used had the following composition:

Alloy 3003 manganese 1 to 1 , 5 % Composition: silicon 0 , 6 % iron < 0 , 7 %

Impurities: copper <0.2 %

Zinc <0.1 % magnesium <0.05 %

Aluminum: supplement to 100 %

Alloy 6951
Composition:

magnesium 0.40 to 0.80 % < 1 O, 10 silicon 0.20 up to 0.50 % < 0, 20th copper 0.15 to 0.40 < 0, 15th iron <0.8: 00 Contaminants: : Manganese zinc other Aluminum: Supplement on

The panels were placed in water containing 263 parts per million parts (ppm) of chlorine ion and 48 parts for one month contained per million parts of sulfations. These treatments were carried out at different temperatures.

After this time, the weight loss was determined. The ^T .verte obtained are summarized in the table below: '

309849/0560

■ - ίο -

water
at 20 Tabel CMl Type of 41
25th
25th (me; / dm) corrosion alloy Weight loss water
at 90 ⁰ C Pitting
(piqüres)
Pitting
uniform • water
⁰ C. at 60 ⁰ C 17th
22nd
12th 3003
6951
inventive
according to 35
67
33

It can be seen that the alloy according to the invention is significantly better than the two comparison alloys which are usually used for the production of heat exchangers. Thus, it is at room temperature better than the alloy 3003 and is better than the alloy 6951st at 60 ⁰ C. At 90 C it is superior to both comparative alloys mentioned. This superiority of the alloy according to the invention is even more clearly expressed when the type of corrosion is examined. The absence of pitting corrosion (pits) in the alloy according to the invention is an important safety feature in heat exchangers with very thin walls, such as, for example, in radiators for automobiles. If these elements are made of light alloys that are subject to corrosion by pitting, they are completely destroyed after an extremely short period of operation.

c) Behavior towards erosion by water.

The tests of the erosion behavior were carried out by deionized water in flat tubes with an internal cross section of 15 x 1.5 μ was circulated at high speed, following the same sequence of pretreatments as listed in the previous example.

The erosion resistance was determined by determining the weight loss after a test duration of 200 to 500 hours and

309849/0560

determined by extrapolation over a period of 2000 hours. The deionized Y / ater was at a rate between 1 to 5 m per second at temperatures of 50 ⁰ O 80 ⁰ C and passed through the tubes. ■

In this way it was found that at 50 ⁰ C and one. Speed of 2 m / sec the weight loss after a test duration of 2000 hours for the alloy according to the invention corresponded to a thickness reduction of 21 microns and also for a comparison alloy 3003 a thickness reduction of 21 microns, v / when the speed was increased from 2 to 4 m / sec, the reduction in thickness was 25 or 28 microns and was therefore less for the alloy according to the invention. At a temperature of 8O ⁰ C, the thickness reduction was 6 and 13 microns at 2 m / sec and 13 or 18 microns at 4 m / sec, indicating a considerable superiority of the invention alloy compared to the alloy 3003rd

309849/0560

Claims (7)

Claims 1 .. · / Alloy suitable for soldering based on aluminum, magnesium and silicon, characterized that it has the following composition: Magnesium 0.20 to 0.70 % Silicon * 0.30 to 0.50 % Impurities ^ 0.80 % Aluminum supplement to 100% the metals usually present as the most important impurities are present in amounts of no more than 0.25 % iron, 0.05 % copper, 0.20 % zinc and 0.15 % manganese. 2. Alloy according to claim 1, characterized that it has the following composition: , Magnesium 0.45 to 0.65 % Silicon 0.35 to 0.47 % Impurities ^. 0.60 %, with the shares of Iron ^ 0.23 %, copper ^ 0.02 %, zinc 4 0.10 %, and manganese ^ - $ 0.08. 3. Alloy according to claim 1 or 2, characterized in that it has an additional content of one of the elements beryllium in a proportion of up to 100 parts per million parts and lanthanide elements in a proportion of up to 0.5 % _o 4. Use of a solderable alloy according to claims 1 to 3, characterized by the fact that one 309849/0560 a) a solder alloy according to a process known per se based on aluminum-silicon on an aluminum alloy - 'tion of the following composition applies; Magnesium 0.20 to 0.70 % Silicon 0.30 to 0.50 % Impurities ^ .0.80 %, where the content of iron 4 0.25 %, of copper 4 0.05 %, Zinc ^ 0.20 % and Manganese ^ 0.15 % ,
Aluminum supplement to 100 %, b) then soldering is carried out at 600 to 620 ⁰ C in a ventilated oven under a regulated atmosphere or under vacuum, c) under a gas flow with a velocity of e "u about 1 ° C / Second cools, d) as the final stage, optionally after rinsing and pickling of the soldered alloy, a thermal hardening treatment carried out by heating to a temperature of 150 to 245 C for 10 minutes to 1 hour, 5. Use according to claim 4, characterized that the solder on the inside or the outside of a body made of the aluminum-magnesium-silicon-bas is Ie gation 'is ordered. . 6. Verv / end according to claim 4 or 5, characterized that one of the base alloy between the solder alloy and the base alloy Alloy arranges, which, however, is free of magnesium. 309849/0560 7. Use according to claims 4 to 6, characterized that the thermal hardening treatment at a temperature of 220 to 240 ° C for 15 to 30 Minutes. 309849/0560