US3666448A - Copper/iron/aluminium alloys - Google Patents

Abstract

COPPER/IRON-ALUMINIUM ALLOYS OF THE BASIC COMPOSITION (WEIGHT PERCENTAGE) 35 TO 75 COPPER, 20 TO 50 IRON AND 5 TO 15 ALUMINIUM AND COMPRISING A MATRIX OF A COPPERRICH SOLID SOLUTION PHASE WHICH CONTAINS A DISPERSED IRONRICH SOLID SOLUTION PHASE, HAVE AT LEAST ONE ALLOY ELEMENT ADDITIONALLY PRESENT TO ENNOBLE THE IRON-RICH PHASE AND/OR TO PROVIDE AN ADHERENT PROTECTIVE FILM ON THE IRON-RICH PHASE. ADDITIONS SELECTED FROM THE GROUP NICKEL, CHROMIUM, TUNGSTEN, MOLYBDENUM AND COBALT, ARE MORE LIKELY TO ACT AS ENNOBLING ELEMENTS AND THOSE SELECTED FROM THE GROUP TITANIUM, NIOBIUM, TANTALUM, ZIRCONIUM AND SILICON, ARE MORE LIKELY TO BE FILM-FORMING AGENTS. PREFERABLY NOT MORE THAN ABOUT 15 PERCENT OF EACH ADDITIVE ELEMENT IS PRESENT, IN HTE CASE OF NICKEL, THE RANGE OF 3 TO 12 (WEIGHT) PERCENT IS PREFERRED AND IN HTE CASE OF CHROMIUM, 3 TO 9 (WEIGHT) PERCENT IS PREFERRED.

Description

United States Patent Office US. Cl. 75-122 5 Claims ABSTRACT OF THE DISCLOSURE Copper/iron/aluminium alloys of the basic composition (weight percentage) 35 to 75 copper, 20 to 50 iron and 5 to 15 aluminium and comprising a matrix of a copperrich solid solution phase which contains a dispersed ironrich solid solution phase, have at least one alloy element additionally present to ennoble the iron-rich phase and/ or to provide an adherent protective film on the iron-rich phase. Additions selected from the group nickel, chromium, tungsten, molybdenum and cobalt, are more likely to act as ennobling elements and those selected from the group titanium, niobium, tantalum, zirconium and silicon, are more likely to be film-forming agents. Preferably not more than about 15 percent of each additive element is present. In the case of nickel, the range of 3 to 12 (weight) percent is preferred and in the case of chromiurn, 3 to 9 (weight) percent is preferred.

This invention relates to alloys that are basically copper/ iron/ aluminium alloys. It has been found that alloys of the composition (weight percentage) 35 to 75 copper, to 50 iron and 5 to 15 aluminium are susceptible to hotworking to yield materials that have useful mechanical properties. Such materials are described in British patent specification No. 1,137,123; these materials comprise a matrix of a copper-rich aluminium-containing solid solution phase in which is dispersed an iron-rich solid solution phase also containing aluminium as described in that specification. In an alloy of this kind the relative hardnesses of the two phases are such that hot-working of the alloy, possibly followed by cold-working, converts the dispersion to a fibrous form which acts as reinforcement for the matrix; the mechanical properties of the alloy are thereby enhanced.

It has been found that, in spite of their good mechanical properties, these alloys suffer from the point of corrosion. It is evident that it is unlikely that alloys of the basic composition will be of use, for instance, under marine conditions and, even under ordinary atmospheric conditions, there is a tendency for loose oxide to form on the alloys.

Corrosion resistance, is, of course mainly comparative. The criterion to be applied in assessing the value of any particular material from the point of corrosion resistance will vary depending largely on the environment in which it is intended that the material shall normally be used. The material may perform satisfactorily when subjected to the well-known test involving immersion in a 3% saline solution and a good rating as a result of submission to such a test may provide enough evidence that a particular material would stand up to, say, marine conditions. However, such a test may not show that that particular material may prove to be highly satisfactory from the point of being tarnish free-that is, that it will suffer exposure and use under ordinary domestic conditions without undue discolouration due to surface action (this is not to say that all materials suitable for marine use will also be tarnish free). Another material, while not being suitable 3,666,448 Patented May 30, 1972 for the extremes of marine use, may be highly satisfactory for use in a corrosive atmosphere at higher temperatures than normal atmospheric temperature where perhaps resistance to scaling may be more important than resistance to discolouration. These are all degrees of corrosion resistance and from the following description it will be appreciated that the object of the present invention is to provide alloys of the basic composition set forth above which will be more resistant to corrosion in at least one of these respects.

According to the invention in a copper/ iron/ aluminium alloy of the basic composition set forth above and having a matrix of a copper-rich solid solution phase which contains a dispersed iron-rich solid solution phase, at least one alloying element is additionally present to ennoble the iron-rich dispersed phase and/or to provide an adherent protective film on the iron-rich phase. Elements suitable as additional elements are comprised within the groups consisting of nickel, chromium, tungsten, molybdenum and cobalt and consisting of titanium, niobium, tantalum, zirconium and silicon. The former are more likely to act as ennobling elements and the latter as film forming agents though, certainly in some cases, notably in the case of chromium, the elements may fulfil an alternative or additional function. In the cases of nickel and chromium, for instance, it can be shown, certainly in some alloys, that chromium when added alone tends to concentrate in the iron-rich phase and that nickel when added alone tends to be concentrated at a slightly higher level in the copper-rich phase. On the other hand, the addition of both these elements in combination causes both to be partitioned to a beneficial extent in both phases and in fact, the solubility of both elements in the iron-rich phase is slightly increased. It is to be noted, however, that these latter observations are not to be interpreted in any way as idenifying the character of alloys in accordance with the invention, nor of course as any explanation of the improvement obtained.

Preferably the alloy in accordance with the invention comprises significant quantities of the additive elements but not more than about 15 (weight) percent of each.

Where nickel and/or chromium are present the nickel content preferably lies between 3 and 12 (weight) percent and the chromium content between 3 and 9 (weight) percent. A particularly suitable quinary alloy has the composition (weight)copper, 0.474; iron, 0.307; aluminium, 0.070; nickel, 0.074; chromium, 0.075. In this particular alloy it is found that the aluminium is distributed substantially equally between the iron-rich and copper-rich phases. Corrosion tests with this alloy have shown that it possesses remarkable corrosion resistance, even when exposed to marine conditions.

According to another aspect of the invention, an alloy which is basically a matrix of a copper-rich solid solution phase containing 5 to 10 (weight) percent of aluminium, the matrix containing an iron-rich solid solution phase which contains about 5 to 10 possibly up to 20 (weight) percent of aluminium also includes both nickel and chromium.

Whereas in British Patent No. 1,137,123 referred to above, accent is on the fibrous form of the iron-rich phase, it is not intended that the scope of the present invention should be limited to materials wherein this phase has such a form. In the case of the quinary alloy mentioned above, for example, it is found that, though the disperse iron-rich phase is not of fibrous form the alloy possesses good mechanical characteristics and at the same time is remarkably corrosion-resistant in both the worked state and as cast.

Inorder that the improvement obtained in a copper/ iron/aluminium alloy by exercise of the invention may be more clearly understood, reference should be made to Tables I and II below.

Table I shows the composition (weight percentage) of the basic alloy tested-Alloy A and also those of a number of other similar alloys in which nickel and/ or chromium are includedAlloys B, F, G, H, I and K. These latter alloys are grouped together in that they represent a series of alloys in which the nickel content of the quinary is varied for aluminium and chromium contentsof substantially constant proportions. Table I also includes the compositions of other alloys Alloy D which contains nickel and chromium in substantially equal though comparatively low proportions, Alloy M which is characterised by lower aluminium content, Alloy L which contains carbon and Alloy C and Alloys E and I which latter three alloys contain nickel and chromium respectively only.

The alloys of the invention range from being ferromagnetic to non-magnetic and in colour from steel grey to champagne.

TABLE I Fe A1 C1. Ni O 4 proves roughly in .proportion to the amount of nickel present. This may give some guide as to the choice of alloy for a particular use. The tests for alloy M are continuing but this alloy is obviously particularly corrosion resistant. v

Alloyv D, possibly because the chromium and/0r nickel contents are low, shows up slightly less favourably than the others containing nickel and chromium.

Alloy L containing carbon is found to be heat-treatable after working so that the hardness can be controlled; its corrosion resistance is good. Although Alloy C does not show up well in these very severe tests, it is found to be reasonably tarnish resistant. Alloy I does not show up favourably in comparison with Alloy A in the saline solution test, but it is nevertheless found to be very good from the point of being tarnish free; it is highly suited to the production of household cutlery and, in fact, appears to be a good substitute for stainless steel. For this reason it and other alloys according to the invention may have architectural applications.

It appears that some of these alloys are readily hotrolled, some are readily cold-rolled and some may be both hot-rolled and cold-rolled.

Specimens of Alloy B in the as-cast state have ultimate tensile strength (-U.T.S.) of about 53 tons per sq. in. with 0.1 percent proof stress {P.S.) of 28 tons per sq. in. and elongation of 17 percent. After cold IOllingto give a reduction in cross-sectional area of about 18 percent, with seven intermediate annealing heat treatments at 970 C., the U.T.S. was over 65 tons sq. in., the RS. 23.5 tons per sq. in. and the elongation about 7 percent.

In the worked state it is expected that the iron-rich phase of at least some of the alloys would take on a fibrous form and that the mechanical properties would be thereby enhanced as described in British patent speci- Table II shows the results in terms of cumulative weight losses in g./ sq. dm./year, after immersion of the particular alloys for a given period of days in the as-east condition in stagnant 3% sodium chloride solution.

It will be seen by comparison of the data for Alloys A and B that the efifect of the addition of nickel and chromium to the ternary alloy is remarkable.

In a hot-rolled state Alloy B showed only slight rust spots after forty-two days in similar laboratory tests and it has been shown that, even after three months immersion, both in the as-cast and hot-rolled states, Alloy B is still very much less rusted than Alloy A and, indeed, than any other ternary copper/iron/aluminium alloy of the basic composition which has been tested.

Both in the as-cast and hot-rolled states, Alloy B retains an untarnished appearance on exposure to air indoors for six months at least and this alloy would therefore be a useful decorative substitute for brass which becomes quite dull under similar conditions within this time.

Though the results shown in Table II for Alloys F, G, H, I and K are not entirely consistent, possibly because the compositions are not exactly comparable, it is seen that the corrosion resistance of this group of alloys imfication No. 1,137,123 referred to above. It is not essential that alloys in accordance with the invention should have that property.

We claim:

1. A copper/ iron/ aluminium alloy of the basic composition 35 to weight percent copper, 20 to 50 weight percent iron and 5 to 15 weight percent aluminium and having a matrix of a copper-rich solid solution phase which contains a dispersed iron-rich solid solution phase, and in which at least one alloying element selected from the group consisting of nickel and chromium is additionally present to the extent of about 3 to 15 percent by weight of the resultant alloy to ennoble the iron-rich dispersed phase.

2. A copper/iron/aluminium alloy as claimed in claim 1, in which nickel is present as a said alloying element, the nickel content of the resultant alloy being in the range 3 to 12 percent.

3. A copper/iron/aluminium alloy as claimed in claim 1, in which chromium is present as a said alloying element, the chromium content of the-resultant alloy being in the range 3 to 9 percent.

4. A copper/iron/aluminium alloy as claimed in claim 1, in which nickel and chromium are present as said alloying elements, the nickel content of the resultant alloy being substantially in the range 3 to 12 percent and the chromium content being substantially in the range 3 to 5 9 percent.

5. A copper/ iron/ aluminium alloy containing basically 35 to 75 weight percent copper, 20 to 50 weight percent iron and 5 to 15 Weight percent aluminium and which is basically a matrix of a copper-rich solid solution phase containing 5 to 10 Weight percent aluminium, the matrix containing an iron-rich solid solution phase which contains 5 to 20 weight percent aluminium, the alloy also including nickel and chromium each to the extent of from about 3 to 15 percent by weight of the resultant alloy. 15

References Cited UNITED STATES PATENTS 1,369,818 3/1921 Kosugi 75-162 X 2,027,997 1/1936 Mishima 75-122 3,384,517 5/1968 Harper et a1. 14831 X OTHER REFERENCES Transactions of AIME, vol. 180, 1949, pp. 32-37.

CHARLES N. LOVELL. Primary Examiner US. Cl. X.R.