US3183588A - Production of alloy-clad articles - Google Patents

Description

United Patented May 18, 1965 3 Claims. for. 29-529 This invention relates to the production of alloy-clad copper-containing articles. It is known that it is possible to cause aluminium to diffuse into copper and it has been established that electrolytic copper and oxidized copper behave differently. In the latter case, the diffusion is slowed down slightly and the presence of a very porous and friable external layer as well as of oxide grains reduced by the aluminium, not only on the surface but down to an appreciable depth, has been observed.

Copper thus treated, in which an aluminium bronze has been formed down to a certain depth, has not had any industrial application, and the few attempts made to use it have been unsuccessful.

'It has now been found that copper-containing articles which have been subjected to a treatment such that aluminium diffuses into the surfaces thereof are suitable for various applications, by virtue of, more especially, their resistance to surface corrosion, and their thermal and electrical conductivity, provided that they are subjected to a mechanical surface treatment. It has also been found that there is formed on the surface of a crude copper article which has undergone a dilfusion treatment, especially when the diffusion has been carried out with a cement, a thin, grey film which is hard and adherent and into which copper has migrated, and this film considerably impairs the properties of the article.

The present invention accordingly comprises a process for the production of a shaped alloy-clad article having a copper-containing core which comprises subjecting a copper-containing article of the desired shape and having an oxide-free surface to a treatment in a non-oxidizing atmosphere such that aluminium, optionally mixed with other elements, diffuses into at least part of the said surface, and thereafter removing mechanically the surface film on those surfaces into which the aluminium has diffused so as to expose the layer of aluminium bronze produced.

The removal of the surface film may be carried out, for example, by tumbling until the yellow colour of the aluminium bronze has replaced the initial grey colour.

The oxide-free copper used as starting material may be industrially pure copper or an alloy of copper and other elements, more especially chromium, zirconium, tellurium, phosphorus or zirconium. Among these alloys, there may be more particularly mentioned those containing from 0.2% to 1.2% of chromium, or from 0.1% to 1% of zirconium, or from 0.1% to 3% of tellurium, or from 0.05% to 0.1% of zirconium and from 0.01% to 0.025% of phosphorus.

The shaping of the article to be clad may be carried out by any appropriate industrial process so as to obtain the desired configuration, for example by casting and, optionally, rolling, by grinding, or by machining from a semi-finished product such as a sheet or bar.

The diffusing operation may be performed by any known method, for example by deposition of aluminium on copper followed by hot diffusion, or by cementation, the latter method being generally preferred.

In the first case, the aluminium may be deposited upon the copper by any of the following methods: by application of an aluminium-based paint to the coppe article; by electrolysis (electrolytic deposition of aluminium from a molten salt bath); by immersion of the copper in a molten aluminium bath; by exposure of the copper to aluminium vapour (vapour coating in vacuo); or by volatilisation of a volatile aluminium salt and deposition on the copper.

The aluminium thus deposited is then diffused by heating the Whole to a high temperature in a furnace under a neutral or reducing atmosphere.

The resulting aluminium bronze layer has only a very small thickness; however, it is not possible by these methods to produce a complex bronze by causing a mixture of metals containing, for example, iron or nickel to diffuse into copper.

In the second case, there is disposed around the article to be cemeted, or against a portion of its surface, a pulverulent cement consisting, for example, of an ironaluminium alloy, and the whole is heated to a high temperature (e.g. about 1000 C.) in a furnace under a neutral or reducing atmosphere. Diffusion takes place between the two solids present, and the process may be accelerated by the presence of an activating agent such as aluminium chloride or magnesium chloride.

The proportion of aluminium in the alloy may vary substantially. In many cases, it is sufiicient to employ a commercial alloy containing from to of alu minium, but alloys having lower and higher contents are also suitable as will be apparent later on.

The basic cement, for example the iron-aluminium alloy, may contain in variable proportions various other elements which dilfuse into the copper at the same time as the iron and the aluminium, and there are then obtained complex bronzes whose mechanical properties are superior to those of a binary copper-aluminium alloy. Among the possible additional elements, there may be mentioned nickel, manganese, silicon, titanium, zirconium, tantalum, vanadium and beryllium. These additional elements may be used alone or a plurality thereof may be employed simultaneously. The maximum content of a single element used alone is of the order of 5% and the maximum total content of a plurality of elements is of the order of 15%.

The maintenance of a non-oxidising i.e. neutral or reducing, atmosphere in the diffusion chamber, for example the cementation furnace is a factor of great importance because it obviates the deleterious influence of oxygen and the danger of explosion. The non-oxidising atmosphere may consist of nitrogen and/or one or more rare gases, such as argon or helium, of hydrogen, of carbon monoxide or of a gas containing it, such as poor gas, or of one or more saturated lower hydrocarbons such as methane or ethane.

The temperature and the duration of the heating affect the depth of diilusion. Thus, for example, in the case of a solid cement such as an iron-aluminum alloy or a 7 complex cement, the most favourable diffusion temperature is in the neighbourhood of 1000 C., and since the depth of diffusion increases with time or temperature the depth for a given temperature is greater as the heating period is longer, and that for a given time is greater as the temperature is higher. Thus, in the case of a simple cement (iron-aluminium alloy), the depth of difliusion mentand the temperature and, if necessary, the quantity of activating agent, to produce an aluminium bronze layer of variable thickness according to requirements.

That portion of the' copper into which pure aluminium or a complex cement has diffused possesses the mechanical, physical and chemical characteristics of the binary or complex aluminium bronze, as shown in the foliowing table.

electricity. Its electrical conductivity'is of the order of -15% IACS (IACS=Interna-tional Annealed Copper Standards; annealed pure copper has 100% IACS). In association with copper, therefore, aluminium bronze reduces the conductivity of the former. This reduction is a function of the ratio of the cemented and unccmensted cross-sections (or volumes) present.

The articles based on copper or copper alloy and made continuity (filiation) of the surface down to the copper core.

As an illustration of the suitability of employing high aluminium content, if an iron-aluminium alloy having an aluminium content of from 60 to 80 percent is used as a cement and the diffusion treatment is effected under specific conditions viz. at a temperature between 950 and 1020 C., preferably about 1000 C., and for a period between 1 hour and 3 hours, preferably about2 hours, a diifusion layer having a high iron content is obtained between the aluminium bronze and the surface film to be removed mechanically.

The elements in the diifusion layer are the same as in the aluminium bronze located underneath but in a different proportion as will be precised below.

The iron content which is very high on the side of the diffusing face decreases gradually towards the pure copper zone; to a like extent and in the same direction there is found a gradual increase of the aluminium content and the copper content.

A microscopic examination showed the presence of various metallographic components and a structure continuity (filiation) from the cutter difiusing face to the pure copper core zone.

The chemical analysis of the components was made 'by means of an electronic probing device. Near the diffusing face there were many crystals of a grey com ponent havinga high iron content surrounded with a solid solution. Then came a zone where eutectoid and a solid'solution were found, both with a high aluminium content, a high copper content and a low iron content. Thereafter pure copper was found.

The grey component was a ternary mixture Fe-ALCu I with the following respective contents by weight:

84.10 percent Fe 5.10 percent Al 8.60 percent Cu That very hand ternary mixture was found to impart to the whole layer having a high iron content a very great hardness (between 400 and 500. Brincll), a great resistance to wear and a good resistance to corrosion at highv temperature.

The mechanical properties of the binary or complex aluminium bronze may be improved by a thermal quench-z ing and temper hardening treatment. Thus, a binary bronze containing 9% of aluminium possessesin the crude cast state a tensile strength of about 45 kg/mmF, After quenching and temper hardening, the tensile strength is about 56 kg./mm.

As compared with pure copper, the binary or complex aluminium bronze is not a good conductor of heat or in accordancewith the invention are characterised by the presence of aluminium optionally accompanied by other elements diffused into the base metal from all or part of their external surfaces to a depth whichzis a fraction of the total thickness of the article. Their surfaces are free from an adherent coating consisting essentially of iron and aluminium into which a little copper has diffused, and which appears 'on these articles after the diffusion treatment but before the mechanical treatment for the removal of the said coating. Generally speaking, they are useful as articles in which good electrical conductivity or good thermal conductivity,. or both, are required in association with good resistance to corrosion.

Examples of specific articles which may be produced in accordance with the invention include more especially tuyeres or tuyere elements for blast furnaces, heat exchanger elements, electric conductors and contacts, more especially contact clips and plates for electrodes, resistance welding electrodes, bralce discs and ingot moulds. It is to be understood that such parts can be directly obtained by application of the process hereinbefore described or by conversion, for example, by cutting or deformation of intermediate products obtained by this process. a

Blast furnace tuyeres are generally of tubular shape composed of three parts, the block, the skirt and the nose piece, which are normally assembled by welding or brazing. The tuyere is intended to introduce into the hearth a hot blast at a temperature of about 800 C. Its walls are hollow, so that it may be vigorously cooled by the passage of water through its interior during the operation of the furnace. The vulnerable part of the tuyere'is the nose piece, which is continuously in a corrosive medium at high temperature. The ambient temperature in the furnace is about 1500l700 C. and the skin temperature of the tuyere is about 700-850 C. The nose piece is in addition subjected to violent abrasion due to the friction of the materials descending to the tap hole.

Tuyeres are generally made of copper which is as pure as possible. Although the, nose piece is often coldharnmered before being fitted, the temperatures reached cause annealing of the materiahwhich then no longer has adequate mechanical properties for resisting abrasion. In addition, complex corrosion effects are observed which render the nose piece of the nozzlerelatively fragile and reduceits strength.

. Using the process of the invention, a tuyere nose piece may first be produced from non-oxidised copper by one of the usual methods, and thereafter brought into the form of a hollow-walled ring for the circulation of a cooling fluid, for example by deep drawing or by moulding, and' thereafter subjected to a treatment such that aluminium ditfuses into the surface if desired accompanied by otherelements, as described above at least over the portion which is most exposed to high temperatures and abrasion, that it to say, its external periphery at the outlet end. The tuyere then offers better resistance to high tempera- 3 tures and erosion. The diffusion treatment may be extended to all or part of the skirt and if necessary to the block as well.

Electrode clips, for example for electric furnaces, connect the electrodes and electrical contacts to the current supply conductors. The electrodes are also suspended above the furnace by such clips.

The good heat exchange coefficient of copper with air and its excellent conductivity make it the best metal for these current supply plates, which are at the same time heat exchangers. However, copper has two major disadvantages, which prohibit its use in some cases: (a) it deforms readily, especially at elevated temperatures; and (b) it has a low resistance to corrosion in some wet or dry corrosive media. Thus, with hot gases such as oxygen or fluorine the corrosion of copper is so rapid that it cannot be used. In a fluorinated atmosphere at 500 C., a copper plate loses 36 mm. per year.

At present, contact plates are generally constructed of brass, and are abundantly cooled by water circulation (conductivity of brass: -25% of that of copper). It is possible by means of the invention to produce such contact plates and clips from non-oxidised copper or copper alloy clad with an aluminium bronze which can be used without any internal circulation of cooling fluid necessarily having to be provided. In accordance with the invention, such parts may have external fins or similar surface features which impart thereto a Wide surface for thermal exchange with the atmosphere. Their cooling may then be improved, if desired, by the simple forced passage of air. It is thus possible by means of the invention greatly to reduce the weight of such plates or clips, while ensuring longer useful life thereof, and to simplify the cooling means.

As brake discs, more especially for jet aircraft, there are at present employed either steel discs, which are bad conductors and which increase the cost of the already very expensive landing gear, and the efiiciency of which is low, or copper discs, which are good conductors, but whose mechanical characteristics at high temperature are poor.

In braking, the brake discs of an aircraft may absorb as much as about 800,000 kg.-m. in energy. The temperature of the disc is brought to 900-950 C. in a few seconds. At this temperature and under the pressure of the friction linings, the copper is squeezed and the deformation remains permanent.

Another disadvantage of copper is its low resistance to corrosion at high temperatures in a medium having a high carbon dioxide and carbon monoxide content. Now, the decomposition of organic substances in the brake linings liberates carbon, which immediately forms an oxide, probably carbon dioxide. At high temperature and under low pressure, the copper begins to crack. These cracks become deeper and deeper in time until the brake disc becomes unserviceable.

Discs which are much more satisfactory from the viewpoint of corrosion cracking may be obtained by application of the present invention. In order to obviate the disadvantage of hot flow, it is advantageous to make the discs not of pure copper, but of a copper alloy having high conductivity and mechanical properties imparting excellent resistance to hot flow, while the surface layer of aluminium bronze imparts corrosion resistance.

From the copper alloys having high electrical and thermal conductivity, there may be chosen as support any of the following alloys:

(1) Chromium copper: (Cr between 0.2% and 1.2%)

subjected to a' heat treatment (quenching and temperhardening); after the completion of the heat treatment, it has the following properties: Tensile strength, 33 to 35 kg./mm. Brinell hardness, 95 to 130 kg./mm. and Electrical conductivity, to IACS.

(2) Zirconium copper: (Zr between 0.1% and 1%) subjected to a heat treatment (quenching and temper hardening) after completion of the heat treatment, it has the following properties: Tensile strength, 33 kg./mrn. (approx); Brinell hardness, to kg./mm. and Electrical conductivity; 8090% IACS.

(3) Tellurium copper, tellurium finely dispersed in a mass of copper imparts thereto hot rigidity without greatly affecting its conductivity.

(4) Phosphorus-zirconium copper (Zr between 0.05% and 0.1% and P between 0.01% and 0.025%); its electrical conductivity is 8595% IACS and its resistance to hot flow is excellent.

If the alloy chosen as support is a structurally hardened alloy (CuCr, Cu-Zr), it is possible after the diffusion operation to apply to the whole the heat treatment desirable for the base alloy: viz (1) heating to about 1000 C. and water quenching, and (2) heating to about 500 C. (temper hardening).

The aluminum bronze also undergoes in the course of these treatments structural variations similar to those of the base alloy, which are beneficial to its mechanical properties.

I claim:

1. Process for the production of a shaped alloy-clad article having a copper-containing core which comprises the steps of (a) applying a metal selected from the group consisting of aluminium, iron-aluminium alloys, and ironaluminium alloys containing at least one alloying element selected from the group consisting of manganese, nickel, silicon, titanium, zirconium, tantalum and vanadium, mixed with an activating agent selected from the group consisting of aluminium and magnesium chlorides to an oxide-free, copper surface of a shaped copper-containing article, (13) heating the said article in a non-oxidizing atmosphere to 950 to 1020 C.. so as to cause the aluminium to diffuse into the copper, and (c) removing References Cited by the Examiner UNITED STATES PATENTS 2,541,813 2/51 Frisch et al 117131 X 2,664,874 1/54 Graham 117131 X 2,876,137 3/59 Drummond 29199 X FOREIGN PATENTS 308,353 7/30 Great Britain.

WHITMORE A. WILTZ, Primary Examiner.

Claims (1)

1. PROCESS FOR THE PRODUCTION OF A SHAPED ALLOY-CLAD ARTICLED HAVING A COPPER-CONTAINING CORE WHICH COMPRISES THE STEPS OF (A) APPLYING A METAL SEELCTED FROM THE GROUP CONSISTING OF ALUMINIUM, IRON-ALUMINIUM ALLOYS, AND IRONALUMINIUM ALLOYS CONTAINING AT LEAST ONE ALLOYING ELEMENT SELECTED FROM THE GROUP CONSISTING OF MANGANESE, NICKEL, SILICON, TITANIUM, ZIRCONIUM, TANTALUM AND VANADIUM, MIXED WITH AN ACTIVATING AGENT SELECTED FROM THE GROUP CONSISTING OF ALUMINIUM AND MAGNESIUM CHLORIDES TO AN OXIDE-FREE, COPPER SURFACE OF A SHPAED COPPER-CONTAINING ARTICLE, (B) HEATING THE SAID ARTICLE IN A NON-OXIDIZING ATMOSPHERE TO ABOUT 950* TO 1020*C. SO AS TO CAUSE THE ALUMINIUM TO DIFFUSE INTO THE COPPER, AND (C) REMOVING MECHANICALLY THE SURFACE FILM ON THEOSE SURFACES INTO WHICH ALUMINIUM HAS DIFFUSED AND EXPOSING THE LAYER OF ALUMINIUM BRONZE PRODUCED.