US2288513A - Alloy - Google Patents

Description

-multitude of galvanic couples.

Patented June 30, 1942 ALLOY Louis Henri Francois Canac andEmilc Auguste Marie Antoine Segol, Toulon, France No Drawing. Application June 19, 1939, Serial No. 279,992 In France July 11, 1936 4 Claims.

Our invention relates to light and ultra-light alloys containing aluminum and magnesium. More particularly it relates to aluminum-magnesium base alloys and a method of making the same whereby certain desirable properties in I such alloys are assured. This application is a continuation-in-part of our application Serial No. 150,880, filed June 28, 1937.

The principal object of the invention resides in the provision of a self-protecting filmcn the surface of thealloy which guards the alloy from corrosion in sea water and the like. This film has the remarkable capacity of cicatrizing. That is, if the film is fractured or broken, this fracture is immediately closed up or healed by the automatic formation of a protective scar.

Ordinary aluminum magnesium base alloys heretofore known do not possess this remarkable property. While some of the literature has given examples of aluminum-magnesium base alloys which are resistant to corrosion, no example has been disclosed of an alloy having a self-healing protective film, and no disclosure, of which we are aware, has in any way taught how an alloy having such a remarkable property can be produced particularly with any degree of assurance.

The invention is based on a remarkable discovery we have made after many experiments and is based on a new principle.

According to this new principle and discovery, an alloy is formed of aluminum and magnesium, and by utilizing predetermined proportions of these base metals, and by adding one or more other metals which meet very. rigid requirements as to amounts and properties, there is automatically formed on the surface of the alloy a uniform, adherent leak-proof, protective film which possesses the astounding property of cicatrizing (forming a scar, healing, closing up) immediately after fracture.

It is consequently the principal object of our invention to provide such analloy and a method whereby it may be produced, not haphazardly and perchance occasionally, but every time the dictates of the following specification are followed.

A more specific object of the invention is the provision of an alloy having a self-protective and self-healing film and having a finely heterogeneous, approximately eutectic structure which, when certain requisites of the invention are carried out, results in the formation of a These galvanic couples, being finely distributed, assure the rapid formation of the protective film in the presence of a normally corrosive agent such as sea water.

As already indicated the results desired can only be obtained by rigidly observing certain requisites. Particularly these requisites will now be described.

The alloyhas a base of aluminum and mat,- nesium. These base metals should be employed only in an extremely pure state. Impurities should be avoided and in any case should be less than 0.10%. This is particularly so of iron and silicon whose presence is exceptionally undesirable and even fatal to the results desired.

When the base of the alloy is such that aluminum predominates, then the proportion of magnesium present should under no circumstances be less than 10%. This percentage is the critical low percentage for magnesium. The many experiments carried out in making the invention demonstrated that the important results relative to the self-healing film'and the mechanical properties of the alloy do not begin to manifest themselves except when the percentage of magnesium used is 10% or greater. The results efiected by the invention are increasingly manifest when the proportion of magnesium is greater than 10%.

Moreover, these results are obtained with proportions of magnesium greater than 50%. The invention thus extends to the so called ultralight alloys in which magnesium predominates.

The lower and upper limits for aluminum are respectively 1% and An alloy containing only aluminum and magnesium even with the proportions given above will not give the results of the present invention. In addition to these metals, in the proportions set forth, we have found that the invention can only be carried out by carefully selecting and adding an additional metal or metals in accordance with specific requirements.

The additional metal must first of all be easily oxidizable.

Secondly, the additional metal should be more precious than the base metals. Any other. metal not responding to these conditions should be ex.- cluded as an impurity inconsistent with the object desired.

The oxidizing property of the addition metal acts primarily in the electrolytic formation of unattackable oxides or oxychlorides, which make up the protective self-healing film. This, however, is only produced by galvanic couples formed between the addition metal and the base metals and in which the ions are displaced from the particles of the addition metal by the base metal. Hence, the requirement that the addition metal should be more precious than the base metals aluminum and magnesium.

When mention is made herein of metals which are more precious than the base metals, reference is had to the electromotive series which lists the metals with respect to their activity, that is, the ease with which they give up electrons. In general, as is well known, each metal displaces the ions of those which follow it in the list.

Another requirement of the addition metal is that it must be capable of forming a eutectic with at least one of the base metals and should be present in an amount which preferably will ap-- proximate the amount which will form a eutectic with the base metals. This contributes to assure a fine distribution of the metals and gives rise to a great number of elementary piles between which eletrolytic action is exerted to a maximum when the alloy is exposed to the action of a corrosive agent such as salt water.

The term eutectic is a definite term known to those skilled in metallurgy. The kinds of metals and the amounts thereof which will form a eutectic with another metal can, of course, be determined from phase diagrams in the technical literature.

When we say that the addition metal should be capable of forming a eutectic mixture with at least one of the basic constituents aluminum and magnesium, and that such addition metal should be present in an amount approximating the amount required to form a eutectic mixture, we intend to cover slight variations. We have found thatv if the addition metal is present in amounts within -30 to +30 of the eutectic amount satisfactory results can be obtained.

Any metals which do not meet these requirements are to be excluded, and insofar as this; invention is concerned such other metals should be regarded as impurities.

While there are several metals which meet the requirements for the addition metal given above and which can be used in accordance with the invention, we prefer zirconium as the addition. metal. Insofar as zirconium is concerned this should be added in amounts ranging from 0.05 to 0.2% to obtain the best results although amounts up to 2%-may be used with the desired results. The lower and upper limits for zirconium. are respectively 0.01% and,3%.

As specific examples of the invention, a satisfactory alloy can be made with:

Magnesium 10 Zirconium 0.2

Aluminum Remainder Our preferred example is as follows:

. Per cent Magnesium 11 Zirconium 0.18

Aluminum Remainder approximate values of the proportion correspond- 75 Per cent ing to the eutectic of the binary diagram of aluminum and the addition metals:

Per cent Antimony 1.1 Chromium 0.40-0.77 Cobalt 1 Beryllium 0.90 Manganese 1.95 Iitanium 0.15 Cadmium 5 In our alloys containing aluminum, magnesium and zirconium, the effect of the zirconium in the alloy may be augmented by the use of a fourth metal. As an example we may have an alloy meeting the requirements of the invention and which consists of:

Per cent Magnesium 10 Zirconium -4 .2 Titanium 1 Aluminum Remainder A preferred example using titanium is as follows:

Aluminum Remainder An alloy of the composition just recited showed very good results when subjected to the action of a corrosive agent. After alternate immersion and emersion at thirty minute intervals in sea water for two months, no appreciable corrosion was observed. Another sample of the same alloy showed no appreciable signs of corrosion after two months continuous immersion.

In all instances the surface of the alloy at the end of the period was covered with protective film. It was found that the protective self-healing film formed more rapidly where the immersionwas continuous.

Mechanical properties of the alloy were found to be particularly good when the alloy is rolled. A breaking strength of 45 kg. and an elongation of the order 17% were obtained. These results are further improved in alloys according to the invention where the proportion of magnesium is about 10.5%.

The titanium may be replaced by other metals provided the conditions referred to above are carried out. The following metals, for exam ple, may be used if proportions preferably approximate the eutectic proportions, as indicated below, are observed:

Percent Cr 1 Be 2 Mn 3 C0 2 Sb 5 Ni 5 Cd 5 Use may also be made of the following as the fourth metal, in proportions preferably less than Boron Bismuth Molybdenum We have found that alloys produced according to the invention may be further improved by heat treatment, notably tempering. This heat treatment is designed also to improve the fineness of precipitation of the crystals formed by the addition metals as well as the so called beta crystals 5(AlaMgz) The temperature and duration of the heat treatment depend both on the percentage of ad-- ditions and the magnesiumcontent of the alloy.

The tempering is not carried to as great a degree where the alloy has a high magnesium content, but, in each case, the duration and temperature thereof have an optimum value. It is particularly important that the duration and temperature should not be carried to coalescence of the precipitated granules.

By way of example, considering the following example:

Percent Magnesium 11.5 Zirconium 0.18 Aluminium Remainder The heat treatment for giving resistance to.

corrosion is then carried out at a temperature ranging from 245 to 320 0., preferably close to this last mentioned value. If it is advisable to effect a supplementary rolling operation, a new treatment is carried out at a temperature of 400 or more.v In a general manner, for the alloys with which the invention is concerned the tempering should be used if the ingot or rolled plates have been very rapidly cooled. The desired structure of the alloy may also be obtained directly by suitable slow cooling of the ingot or of the sheets during the rolling, for example, by

stopping for about fifteen minutes starting from a temperature generally above 300 C., in which the granules can precipitate.

We claim: 7

l. A corrosion resistive alloy having a surface formed of a multiple of galvanic couples which surface when subjected to corrosive influences is capable of forming a self-protective, cicatrizing, film, said alloy consisting of magnesium in the amount of 10%, zirconium in the amount of 2%, and the balance being aluminum, said alloy containing less than 0.1% of impurities, all metals being considered as impurities which are not easily oxidized, are less precious than aluminum or magnesium and which are incapable of forming a eutectic with aluminum or magnesium.

2. A corrosion resistive alloy having a surface formed of a multitude of galvanic couples which surface when subjected to corrosive influences is capable of forming a self-protective, cicatrizing, film, said alloy consisting of magnesium in an amount ranging from 10 to 15%, zirconium in an amount ranging from .05 to 2%, and the balance being aluminum, said alloy containing less than 0.1% of impurities, all metals being considered as impurities which are not easily oxidized, are less precious than aluminum or magnesium and which are incapable of forming a eutectic with aluminum or magnesium.

3. A corrosion resistive alloy having a surface formed of a multitude of galvanic couples which surface when subjected to corrosive influences is capable of forming a self-protective, cicatrizing, film, said alloy consisting of magnesium in an amount ranging from 10 to 50%, zirconium in an amount ranging from .05 to 2%, and the balance being aluminum, said alloy containing less than 0.1% of impurities, all metals being considered as impurities which are not easily oxidized, are less precious than aluminum or magnesium and which are incapable of forming a eutectic with aluminum or magnesium.

4 A corrosion resistive alloy having a surface formed of a multitude of galvanic couples which surface when subjected to corrosive influences is capable of forming a. self-protective, cicatrizing, film, said alloy consisting of magnesium in the amount of 11%, zirconium in the amount of 0.18%, and the balance being aluminum.

LOUIS HENRI FRANCOIS CANAC. EMILE AUGUSTE MARIE ANTOINE SEGOL.