DE1956887A1 - Method and composition for aluminizing metal articles - Google Patents

Description

Dipl. Ing. C. Wallach

Dipl.! Ng. G. Koch ' 1? unv iQßO

Dr. T. Kaibach T £. Court. 1969

8 Munich 2

Kaufinflerstr. 8, Tel. 240275

18366 -

ROLLS-ROYCE LIMITED, Derby / Derbyshire (Great Britain)

Process and composition of the aluminizing of metal

objects

The invention relates to a method and a composition for the use of aluminizing ("pack: aluminizing") of metal objects; in particular, although not exclusively _t, the method is suitable for use-Alurainisieren of objects made of steel.

The method of Einaatz-Alurainisierung is known per se, for example from British patent specification 933 200 of Applicant; the principle of this procedure is that the metal object to be aluminized in an insert " Aluminizing mixture is immersed, which is then in a controlled atmosphere. A minor part of the known process consisted in the fact that the processes required for the aluminizing process required temperature was in some cases unacceptably high, causing undesirable changes in the metallurgical structure of the part to be provided with the metal pull

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Item led.

The present invention aims to provide an aluminizing process that involves a heat treatment works at a relatively low temperature and still provides a satisfactory aluminum coating (it should be noted that here and in the the following description of the term "aluminum coating" is used, although in reality an aluminum alloy coating is generally made,)

According to the invention, the process for aluminizing a metal object is carried out in such a way that the object is embedded in a mixture of 30 to 60% aluminum powder, 30 to 60 % calcined aluminum oxide, and a source of chloride ions, and in this state at least Heated for hours to a temperature in the range between 480 ° C. and 550 ° C., the chloride ion source being able to supply ions for at least the greater part of this heat treatment duration.

The source of chloride ions can either be part of the gas atmosphere. be the sphere in which the heat treatment is carried out,} or it can be a solid component of the aluminizing mixture, or both.

According to preferred embodiments of the invention can be used as source of chloride ions a proportion of 1 to 20% of hydrogen chloride gas in the atmosphere in which the heat treatment is carried out, and / or a proportion of 1 to $ 20 following solid component ·: Zinkohlorid, Aluminlumohlorid, tin chloride, Sllberohlorid , Cadmium chloride, Keliueehlorid, serve in an intimate mixture with the AlUBinisierungszusameeneetzt. Other solid chlorides can also be used, if on the one hand they are sufficiently heat-resistant that they do not decompose when heated,

.A 009624 / 138-7.

however, on the other hand, they are again so unstable that they become decompose quickly enough in the course of the heat treatment to provide the required chlorine ions. As a suitable one The vapor pressure of the solid * chloride "has proven to be the criterion for the desired thermal stability; s-o a solid chloride has been found to have a vapor pressure of 100 min Hg at a temperature in the range of lfSO ° C to 1200 ° C is satisfactory / (Dio vapor pressures were published after that by the Chemical Rubber Company "Handbook of Chemists and Physics," editor Wöast, 48th ed., Definitely.)

Maoh has a preferred embodiment of the invention the mixture for aluminizing has the following composition (in dew. #):

Aluminum powder 30 to 60 %

calcined aluminum oxide 20 to 70 #

as well as one or more of the following solid constituents: zinc chloride, aluminum chloride, tin chloride, silver chloride, cadisiurochloride or potassium chloride in a total amount of 1 to 20 %.

A preferred mixture has the following composition (in Gew.jS):

Aluminum powder 40 to 50 %

calcined aluminum oxide 40 to 60 % zinc chloride 1 to 10 %

When using the above mixture, «a gaseous · Chloride source in the gas atmosphere in which the Heat treatment is carried out, not required; the gas atmosphere can therefore consist of a non-oxidizing Gaus,

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such as hydrogen, or an inert gas, such as such as argon.

In the following the invention is illustrated by means of exemplary embodiments explained.

EXAMPLE 1

First, an aluminizing mixture was prepared according to the invention % the mixture contained 100 g of aluminum powder according to Briti3h Standard Specification 388, with particle sizes of about 35 x 82 microns, 100 pounds of pure calcined aluminum oxide with a particle size of 50 microns, 2 grams of ammonium chloride and 3 g Aluminum fluoride. This composition was poured into a crucible that was open at the top, and a stainless steel specimen was immersed in this mixture. The stainless steel used in this example and in the following examples had the following composition:

carbon 0.08 - 0.20 % chromium 10.0 - I3.O %

Silicon 0.10 - 0.80 % nickel max. 1.5 56

Manganese 0.2 - 1.25 % Molybdenum 0.3 - 0.95 %

Phosphorus max. 0.303 % Niobium 0.1 - 0.7 %

Sulfur max.0.25 % Vanadium 0.1 - 1.0 £

Remainder iron

The crucible containing the alurainization mixture and the test specimen, which was open at the top, was then placed in a tube furnace and heated to a temperature of 500.degree. A hydrogen atmosphere with a proportion of gaseous hydrogen chloride was maintained in the furnace and thus in the crucible. The hydrogen content was added in such a way that its proportion decreased from 13% at the beginning of the treatment to about 1 % at the end of the treatment.

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took; the mean and equal. ^ the preferred is about 10 #.

Conditions were maintained for 24 hours; then became the Sohmelstiog; ©! taken out of the furnace and taken out and examined animal test specimen. In a special example case, a well-adhering coating of 1.1 / 1000 inch picks and good surface conformance reproduction had formed. A © below microprobe analysis of the coating revealed that this coating of 55 wt.% Aluminum with 35 wt. # Iron, 5 wt. # Chromium and the remainder impurities be · stand "This composition of the coating remains substantially the same in Examples 1 to 4.

EXAMPLE 2

Again there was an alurainization mixture according to the invention In this case the mixture consisted of 100 g aluminum, 100 g pure calcined aluminum oxide and 6 g of aluminum fluoride. The particle size of the powder and its Composition were the same as in Example 1. This composition was again made together with a test piece stainless steel in a crucible and this, as in Example 1, placed in a furnace «using the same temperature as in Example 1. However, at in this example hydrogen with gaseous hydrogen chloride during the first two hours as a gaseous atmosphere the next 16 hours argon, and sehlieeiioh during In the last 6 hours, hydrogen was mixed with gaseous Hydrogen chloride used.

Also here the test item was examined after the treatment, where there is an overlay with a thickness of 1.1 / 1000 inches that was well-adhered and. a good surface finish exhibited.

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Eb would in turn be a composition: Dried egg produced in this Pall ICO g aluminum, 100 calcined. Aluminum oxide, 2 g ammonium iodide and ^ g aluminum fluoride. The component sizes were as in Example. Again, a metallic test specimen of a similar type to that in the preceding examples was treated in the mixture at a temperature of 500 ° C. for seven hours in an atmosphere of hydrogen with an addition of hydrogen chloride. After treatment, the sample was examined and found to be coated on the specimen with a Dioke of 0.5 / 1000 Customs found which had a good © _# adhesion and good Oberfläohenbesehaffenheit.

Example 4 -

A mixture according to the invention was prepared which made of 100 g aluminum powder, 100 g pure calcined aluminum * miniumoxide and 20 g of aluminum chloride consisted. The examinee was, as in the previous examples, for three hours at a temperature of 500 ° C in a gas atmosphere. treated from hydrogen with the addition of hydrogen chloride. Thereafter the test specimen was examined. It turned out that he had a " well-adhering aluminum coating with good surface reproduction exhibited. The thickness of the coating was not determined in this example.

Example 5

Ea was a mixture of 100 g aluminum, 100 g pure calcined Aluminum oxide, 10 g zinc carbonide and 6 g aluminum fluoride manufactured. In this and in the following examples, a test specimen in the form of a streamline pile was used treated from the above steel, this

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BATH

Examinee before deai over si rather; ιηά oi. ^ su Barveltng process cleaned, was.

The test specimen was then, as described above, embedded in the mixture in a crucible and heated to a temperature of for six hours in a hydrogen atmosphere with the addition of 5% hydrogen chloride. 550 ° C heated. The specimen was then removed and showed a good quality coating about 2/1000 of an inch thick, consisting of 55 % aluminum, 39 % iron, 5 % chromium and 1 % zinc. The addition of zinc to the coating, which indicates the use of zinc carbon as a source of chloride ions, is particularly expedient since it provides a certain protection of the basic material against electrophilic corrosion.

Example 6

Here the aluminizing mixture consisted of XOO g of aluminum, 100 g aluminum oxide and 10 g tin chloride, the heat treatment huh? dl «same as described above, but existed the * aaa atmosphere. only from hydrogen; the heat treatment Stretched over six hours at 550 ° C.

The test specimen showed a coating of very good quality of 1.5 / 1000 inch didce.

Example 7.

In this case the aluminizing mixture consisted of 100 g of aluminum, 100 g of alurainium oxide and 10 g of zinc chloride. Ih a hydrogen atmosphere with 5 % Chlorifasseratoffzusatz was heated for six hours at 550 ° C.

The obtained, well adhering coating had a thickness of 1.7 / 1000 in.

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Example 8

E3 was a mixture of 100 g aluminum, 100 g aluminum oxide, 6 g of aluminum fluoride and 5 g of zinc chloride were used. Of the The test specimen was in this genius and a gas atmosphere consisting of hydrogen with an addition of hydrogen chloride Heated to 550 ° C for six hours.

After that, the test specimen showed a good quality of 2/1000 inch thickness.

Example 9

The aluminizing mixture consisted of 3 100 g aluminum powder, 100 g aluminum oxide, 6 g aluminum fluoride and 5 g silver chloride. The heat treatment and gas atmosphere were the same as in Example 8.

The sample exhibited a good quality coating 1.8 / 1000 inch thick.

Example 10

In this case, cadmium chloride became a donor of chloride ions used, and the Aluoinisierungsgemiech consisted of 100 g Aluminum powder, 100 g aluminum oxide, 6 g aluminum fluoride and 10 g cadmium chloride. The test item and the heat treatment were the same as in Example 9.

A good quality coating resulted with a thickness from 1.8 / 1000 in.

Example 11

A mixture of 100 g aluminum, 100 g aluminum oxide, 6 g of aluminum fluoride and 2 g of potassium chloride produced,

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Gas atmosphere and heat treatment temperature conditions "were the same as in the previous example, likewise the examinee.

The result was a good coating of 1.5 / 1000 Inch thickness.

From the preceding examples it can be seen that a whole range of chlorides have been found suitable for use in the aluminizing mixture according to the invention to have. It is assumed that the chlorides act as a source of chloride * ions, with these ions being responsible for the transmission of the Effect aluminum from the mixture on the base metal. The chloride ions can form a transition compound with the aluminum, which in turn decomposes when it comes into contact with the metal surface. -

The chloride compounds suitable for this reaction can on: those are restricted, which are enough speed oh decompose in order to supply the necessary ions at the temperatures in question, but on the other hand are relatively stable in order to ensure a continuous supply of ions over the greater part of the heat treatment. It has been found that - insofar as solid constituents of the aluminizing mixture serve as the source of chloride ions - this " Requirement can be translated to the effect that the vapor pressure of the chloride at a temperature in the range of 150 ° C up to 1200 ° C should be 100 mm Hg.

When using a gaseous component as a chloride ion donor, it is of course easy to ensure a continuous supply to replace the decomposed material. When using gaseous HCl it has been found that up to 20 % by volume can be consumed in the treatment atmosphere.

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The invention has been described above on the basis of specific exemplary embodiments explains, concerning the production of coatings on stainless steel; of course that is suitable Coating composition also for treating other fabrics such as stainless steel of a different composition or high temperature resistant alloys on Kolbalt and Nickel base.

Also the proportions of the various components of the mixture can fluctuate within considerable limits, as they are in the introduction to the description and in the following claims are specified.

Patent claim -

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Claims (10)

1956687 it - Patentaas Dr ^ (DD) method zura aluminizing a metal! Object daduroh g 3 k β η η Seich η β t, by embedding the article in a mixture of J> 0 to 60% of aluminum powder, J50 to 60% calcined Aluminiuraoxyd, and a chloride ion source and heated in this state for at least six hours to a temperature in the range between 480 ° C and 550 ° C, wherein the source of chloride ions is capable of supplying ions for at least the greater part of this heat treatment time. 2. The method according to claim 1, characterized ge k «nnzeiohn e t that as exclusive or partial chloride ion Duration"
source, one or more parts of the gas atmosphere in which the heat treatment is carried out are used. 3 «Method according to claim 1 or 2, characterized in that a pest component of the aluminizing mixture serves as the exclusive or partial source of chloride ions. 4. The method according to claim 2, characterized in that g e k η η ζ e i ο h net, that as Cbioridionenquelle a Ctilorwaseerstoff-share the OasatmoephHre serves. Method according to claim 4, characterized in that the hydrogen chloride content of the gas atmosphere is 20 % . 6. Ve: 'drive according to claim jj, characterized in that the Aluminiaierung3gomiseh as Chloridiononquolie up to a total of 30 % one or more of the following Festb © 3tant3teilo: Zinkohlorld, aluminum chloride, 9 Ö 7 UI \ 3 θ 7 Tin chloride, sodium chloride, cadmium chloride or potassium chloride, has in intimate mixture with the Alumlnisierungsgemieoh. 7. Composition for aluminizing metal objects neon the method according to the preceding claims, characterized in that it comprises 30 to 60 pounds of aluminum powder, 20 to 70 % pure calcined aluminum oxide, and a chloride ion donor. The composition according to claim 7 is worthwhile in that it has one or more of the following ingredients as chloride ion donor in an ossaet content of up to 20% : zinc chloride, aluminum chloride, tin oxide, silver chloride, cado chloride or aluminum chloride , having. 9. Addition according to claim 7 or 6, thereby allowing it to contain up to 50 % aluminum powder, 0 to 60 % pure calcined aluminum oxide and up to 10 % pure chloride . 10. Assistance with one or more other people 7 bis 9, marked by the fact that it is one. Has addition of 0 to 5 % Aluninlumfluorld. 11 «Composition according to one of Examples 1 to 11. 009824/1381