NO147387B - PROCEDURE FOR STABILIZING OIL-IN-WATER DISPERSIONS AND STABILIZED LIQUID FOR USE IN PROCEDURE - Google Patents

Description

Aluminum alloy with valuable galvanic properties.

This invention relates to aluminum alloys with used

normal galvanic properties except for use for primary electric cells in accordance with Norwegian patent no. 116 126.

More particularly, it concerns aluminum alloys from which high galvanic currents combined with high galvanic effect can be obtained.

In connection with the use of metals for galvanic applications, one has long been aware of a problem which consists in providing a cheap, commercially available metal with desirable galvanic properties for many purposes. Many metals and alloys have been proposed for this use, and it has also been found that a number of metal compositions have galvanic properties that make them suitable for special applications. The degree of usability for a particular metal naturally depends on the combination of galvanic properties - Cfr. at 48d<1->13/00 per as required for a particular use, and how well this combination of properties can be accommodated by metals and alloys at lower prices.

Alloys containing high percentages of tin in aluminum have been known and studied for many years, and many values have been given for the solubility of tin in aluminum and for the solubility of aluminum in tin. But none of the known alloys of tin and aluminum which have been known have been able to exhibit such a combination of galvanic properties as those which have been obtained according to the present methods.

Aluminum alloys containing large amounts of tin are e.g. have been used as stock metal alloys. There are other aluminum alloy compositions where small additions of tin have been used, e.g. in Al-Cu-based alloys to modify the degree of age hardening.

Accordingly, one object of the present invention is to provide an alloy of aluminum which exhibits improved galvanic properties.

Another object is to provide an alloy with a combination of galvanic properties that can be varied over a wide range

those that are not currently available in the commercially available alloys.

It is also an object to provide an alloy of aluminum with improved galvanic properties which can be produced from aluminum alloys of technical purity.

Other purposes will partially appear or be indicated by the following description.

From one of the further points of view, the object of the invention is achieved by providing a galvanic aluminum alloy containing about 0.1 and 0.5% tin in such a state that said alloy is made galvanically active, while it does not contain more than approx. 1% of elements that may act to mask said galvanic properties.

From the narrower point of view of producing high galvanic currents at high anodic effect, these objects are met by providing an aluminum-based metal alloy containing less than 0.05% silicon, less than 0.1% iron and between 0.1 and 0.3% tin where the alloy is in a homogenized state.

Implementation of these and other aspects of the invention will appear more clearly from the following description. In this description, reference is made to the accompanying drawings, where: Fig. 1 is a representation showing the connection between certain galvanic properties of aluminium-tin alloys and

the silicon content in the alloys.

Fig. 2 is a similar representation showing the same connection

look for aluminium-tin alloys with increasing iron content.

Fig. 3 is a representation showing the connection between the cell potential of galvanic cells containing aluminium, and the amount of current.

It has now been discovered that high galvanic currents associated with high anodic effects can be obtained at greatly reduced costs, when these costs are compared with the costs for corresponding currents produced by galvanic oxidation of previously known metal compositions. The price of electrical energy produced by such galvanic oxidation is in itself so low that additional power sources based on galvanic oxidation of aluminum alloys in

ge the present invention can be made economically competitive with other power sources, such as internal combustion engines, for certain applications. When such economic production of electrical power has been achieved on the basis of this invention, this depends on two principal factors.

The first of these is that it is possible to preserve many of

the highly desirable galvanic oxidation properties of the alloys described in Norwegian patent no. 116 126, where

certain ternary alloying elements are present in the higher purity aluminum-based alloy used in the Norwegian patent, and even improve certain desirable properties of the alloys by such additions. When high galvanic currents of a sustained nature can be achieved, this is partly due to the alloy's ability to develop surface layers upon oxidation of any part of them, these surface layers having an excess of n-type defects in sufficient concentration to significantly increase their conductivity, i.e. to increase the conductivity of such layers by more than 100%.

The achievement of a high galvanic current of a sustained nature and with high anodic efficiency is partly also due to the presence of secondary cathodes in the alloys in a size, shape, distribution and concentration that meet the requirements which are more fully set out below.

Another factor that contributes to providing a high galvanic current at a low price when galvanic oxidation of aluminum is due to the alloys' very clear effect on a heat treatment after casting with regard to the effect of this treatment on regulating the alloys' galvanic properties. This heat treatment after casting can be used to regulate the concentration of tin in metastable solid solution in the aluminum alloy. An important advantage of this treatment after casting is that the amount of tin in metastable solution is brought to a maximum, as it has been found that the higher concentrations of tin in solid solution are essential to obtain higher galvanic currents from the alloy . As will be described more fully below, the possibility of obtaining high galvanic currents in aluminum-based tin-containing alloys, where the aluminum is of lower purity, depends to a large extent on the concentration of tin in the phase solution being brought to a maximum through homogenization treatment.

It is also possible to regulate certain properties of the alloys by modifying the casting process. It is e.g. possible to

increase the size of certain insoluble intermetallic compounds, such as FeAl^, by reducing the cooling rate of the melt during casting to delay solidification, allowing the particles of FeAl^ to grow to a specific size.

Each of these factors will be dealt with in turn with respect to their effect on the production of aluminum alloys with desired gaJ *aniskc properties at low cost.

With respect to the purity of the aluminum base in the galvanic alloys, we saw?. c'.~; impurities commonly found in technically pure aluminum tend to mask the remarkably high development of galvanic current which has now been found possible in aluminum-based alloys with • -ir;.sk activating amounts of tin. In order to provide an inexpensive ga.1 ;...ouinium with high galvanic current and high current efficiency according to this invention, it is therefore necessary not only to provide for the addition of tin in the desired amount and form, but it is also necessary to limit the general pollution level to predetermined low values.

One of the most common impurities normally found in aluminum-based alloys is silicon. It has been found in this connection that aluminum-tin alloys with from 0.1 to 0.3% tin, containing up to 0.05% silicon, will give high galvanic currents if the alloy is in a homogenized state. As shown graphically in fig. 1 high galvanic currents above 500 coulombs are not obtained in a galvanic reference cell for 48 hours when higher concentrations of silicon are present, even though tin is present in quantities that otherwise give high galvanic currents, and this alloy is in a homogenized state.

However, useful galvanic currents are produced by such alloys with a silicon content of 0.05%, as shown in fig. 1, and this shall be explained in more detail below.

If one then looks at the concentration of iron as a commonly occurring contaminant in aluminum, it has been discovered that where the iron content of homogenized aluminum-tin alloys containing 0.1 to 0.3% tin does not exceed 0.1%, high galvanic flows at high anodic efficiency, i.e. above 50% efficiency. As shown in fig. 2, it is seen that at values for iron concentration significantly greater than 0.1%, the values obtained for certain other galvanic properties are reduced below the desirable high values that can be obtained at lower concentrations of iron.

It is thus possible to preserve many of the desirable galvanic and other properties of alloys containing tin in high purity aluminum, even though the tin is present in homogenized form in an inexpensive aluminum base containing up to 0.1% iron, up to 0.05% silicon, and concentrations of other impurities unable to mask these desirable galvanic properties.

It may be advantageous to raise the tin concentration from the preferred range of 0.12 to 0.15% for high purity aluminum base to concentrations of 0.2% and above as the concentration of other impurities increases. If e.g. the silicon content is around 0.05%, the tin concentration is preferably raised to approx. 0.2%.

In order to make the presentation clearer, and the references easier, a number of terms in the preceding and the following description will now be defined.

In connection with one of these definitions, reference is made to the accompanying drawings, where fig. 2 is a graphical representation showing the relationship between the amount of galvanic current produced from a galvanic reference cell and the potential that exists between the cell's electrodes. In fig. 2, the ordinate is the number of coulombs that appear in the galvanic reference cell over the course of 48 hours, and the abscissa is the potential in the closed circuit on the hydrogen scale that is found developed in the reference cell. In general, one will see from fig. 3 that there is a remarkable increase in the amount of current produced by a unit increase in the potential between the electrodes when the potential is more negative than -0.9 volts, compared to the increase in galvanic current produced by a unit increase in the voltage when this is less negative than -0.9 volts.

Due to the very sharp change in the level of the galvanic current that occurs for each unit increase in voltage at voltages more negative than -0.9 volts in the reference cell, in the following aluminum alloys with the ability to produce aluminum alloys with the ability to to produce continuous current in the reference cell at a potential more negative than -0.9 volts be referred to as galvanic aluminum compositions. So far, no aluminum compositions have been known to be capable of producing continuous galvanic current in the reference cell at a potential more negative than -0.9 volts on the hydrogen scale.

As the term "reference cell" is used herein, it refers to a galvanic cell such as that described in the "Journal of the Electrochemical Society", Volume 105, No. 11 (November 1958), beginning on page 629. Such reference cell contains a solution of 0.1-normal sodium chloride in distilled water at 25°C, and the steel and aluminum electrodes are in the form of rods with a square cross-section with a total apparent surface of o 10 cm 2 exposed to the salt solution. The salt bridge used for measuring the potential in the reference pair was placed between the electrodes of the reference cell instead of next to them, as shown in the aforementioned article, and it was connected to a standard calomel electrode to measure the reference potential t in the aluminum steel pair. The calomel electrode is connected approximately to the midpoint of the aluminum-steel pair in the reference electrode. The abscissa in fig. 3 is the potential on the hydrogen scale found to exist between electrodes of aluminum and mild steel when the cell is in continuous operation. The ordinate in fig. 3 is the number of coulombs that were found to flow between the aluminium-steel pair in the reference electrode for 48 hours.

In general, the ternary elements found in the aluminium-tin alloys can be grouped into two categories. The first is the group of impurities found in aluminum alloys due to the process used to produce the alloy, and on

due to the accompanying polluting elements found in the aluminum ore. The second group comprises ternary elements which are intentionally added to the aluminium-tin alloy to modify its properties.

Among the polluting elements, the two most common are silicon and iron, as just mentioned above. In general, other contaminant elements which may mask the galvanic properties imparted with the tin should be kept at concentrations below 0.02%, if high galvanic currents with high efficiency are to be obtained.

But it is possible to incorporate larger amounts of ternary elements in excess of 0.02%, either where such a content has no harmful effect, or where special modifications of the galvanic behavior of them are sought.

In general, it has now been seen that the behavior of the ternary elements when added to aluminium-tin alloys depends on the solubility of the elements in aluminum and their effect on the aluminum lattice. More specifically, it can be said that changes in the galvanic behavior of aluminium-tin alloys which give rise to the addition of ternary alloying elements primarily depend on the effect of the ternary element on the solubility of tin in aluminium- Namely, it is the tin that is dissolved in the aluminum lattice which is primarily responsible for the higher concentration of n-type defects found in the surface layers of aluminum oxide that appear on the surface of the aluminum alloys by reaction with elements in the environment.

It has thus now been found that the ternary additive elements which are included in solid solution and which expand the aluminum lattice, stabilize the tin in solid solution and enable high galvanic currents to be extracted from the alloys. Ternary alloying additions that show this behavior are magnesium, zirconium and bismuth. The use of bismuth as a ternary alloying addition is preferred because it further increases the galvanic current beyond that obtained from corresponding aluminium-tin alloys where this ternary alloying element is missing.

Yet another group of ternary alloying additions are such as

are soluble in aluminum and which cause a contraction of the aluminum lattice. These additions cause a reduction in the amount of tin that remains in solid solution, and they therefore act to reduce the beneficial effects of tin on the galvanic properties. Ternary alloying additions that will contract the aluminum lattice include copper, zinc, manganese and silicon.

A third group of ternary alloying elements are those which have a very small maximum solubility in aluminium, less than 0.05%, and which exist mainly in an insoluble second phase state. The effect of ternary alloying additions as second-phase components

in the alloy lies primarily in a reduction of the anode efficiency. Such second-phase materials have only a small effect on the alloy's yield of galvanic current.

The effect of the addition of certain ternary elements from

these groups on the galvanic properties of aluminum alloys are illustrated in the following table I.

This table shows values for anodic current, anode efficiency and pair potential for aluminium-tin alloys containing small additions of the ternary alloying elements. The values listed first apply to the aluminum-tin binary alloy made by alloying 0.12% tin with high-purity aluminum (99.97

for all the other alloys listed, the ternary element is alloyed into an alloy containing 0.20% tin, with the remainder being high-purity aluminium.

The galvanic properties of the ternary alloys as given in Table I illustrate the grouping of ternary additive elements into the three groups discussed above, based on their effect on the aluminum lattice and on the solubility of tin in aluminum.

Anodic efficiency.

Another critical factor when one wants to achieve high galvanic current economically from aluminum alloys, in addition to the voltage factor discussed above with reference to fig. 3, is the efficiency with which electricity is produced by the galvanic oxidation reaction where metallic aluminum is oxidized to ions by reaction with oxygen, water, chlorine, fluorine or other oxidizing elements or compounds.

Highly efficient galvanic aluminum is an aluminum alloy from which a certain amount of current can be extracted, with withdrawal from an anode made of the galvanic aluminum, from less than twice the amount of metal theoretically needed to provide the given current. Highly efficient galvanic aluminum differs from galvanic aluminum as such in that the term galvanic aluminum denotes aluminum-based alloys, from which usable high current values can be extracted to a persistent degree at a voltage on the hydrogen scale more negative than -0.9 volts, regardless of the amount of metal that is consumed or removed from an anode during the production of said current in a galvanic reference cell.

As for the anodic efficiency of metal alloys containing only tin in solid solution in high purity aluminium, or in a base metal of aluminum with less than 0.05% silicon and less than 0.1% iron, the anode efficiency in such alloys high. It can be of the order of 90% or more for high purity aluminum with 0.02% tin, for example, when electrically connected to a steel cathode both through an external electrical circuit and through an internal electrical desalination circuit. However, if an alloy containing about the maximum dissolved tin is used, then this high efficiency, although high, will often be accompanied by an undesirable "pitting" or pitting. This pitting is an unwanted local penetration of the metal at a greater rate than that which would result from uniform corrosion of the entire anode. The formation of pits can ultimately lead to parts of the electrode separating when the electrode is used for a long time, and to a reduction in the number of ampere-hours obtained per unit weight of the anode metal.

It has now been discovered that by adding second-phase conductive local cathodes, numerous corrosion centers can be produced, and by producing numerous corrosion centers, a desirable uniform corrosion occurs. It has also been discovered that although the addition of a second phase cathode is accompanied by loss of power, a "sacrificial anode" composition can be produced with a combination of galvanic properties that are better than those of other metals.

As an additional, unexpected advantage of adding the secondary tin cathode particles, an increase in the amount of current produced at the anode has been found. Thus, while the efficiency decreased from 70% to 58% when the % content of tin increased from 0.10 to 0.125, the galvanic current in high-purity aluminum increased quite surprisingly by 83

Consequently, another requirement must be placed on alloys according to the present invention over and above the requirement for an increased number of n-type defects in the surface layer formed by anionic reactions. When the alloys are to be used for galvanic purposes as "sacrificial electrodes", particulate secondary cathodes must be present in the anode. In essence, this second requirement is that the secondary cathode must have such a form, composition and distribution in the anode that it induces significant changes in the other factors that

controls the alloy's galvanic properties.

It has thus been found that when a second-phase conductive substance which is insoluble both in the aluminum alloy and in the electrolytes is added to the aluminum-tin anode as finely divided dispersed particulate material, this second-phase substance acts as a cathode.

There is a definite connection between the shape and quantity of the single-phase cathode particles and the galvanic properties shown by the anode where they are distributed as will be described more fully in the following. But in general, you will not get the desired result when there are either too few or too many, or too large or too small particles.

One will therefore realize that the second-phase particles only become active as secondary cathodes when the particles are exposed to the electrolyte environment on the surface of the anode during the electrolytic dissolution of the anode metal.

The term localized corrosion in this presentation means the corrosion that takes place in the vicinity of particulate tin, or another second-phase cathode particle, on the surface of the sacrificial anode.

Because of the intimate contact and close connection between the secondary cathodes and the surface of a sacrificial anode, the anode efficiency is very sensitive to the amount and distribution of the second-phase cathode particles in the sacrificial anode.

With the use of the sacrificial anode in 0.1-normal NaCl as described below, it has been found that in an alloy with one distribution of essentially elementary excess tin in particle form, and where the number and distribution of the particles is sufficient to give a statistically significant sample, where the efficiency of the anode current E is related to a number of other variables in the galvanic process according to the following equation:

where E is the anodic efficiency in percent

m is the mass of surplus tin and other conductive solids

second phase per volume unit,

s_ is the density of the metal in the second phase

K is a constant,

d is the corrosion depth per unit of time, and

r' is the average radius for the second-phase particles under the assumption that the particles are essentially spherical.

On the basis of the above presentation, it will appear that to the extent that ternary alloying elements with very low solid solubility in aluminum are primarily found in an insoluble second phase, where the size and distribution of second-phase particles induces a reduction in s_ or £ in above equation or induces an increase in m or d_ in it, then there will be a lowering of the anodic efficiency. Preferably, the concentration of insoluble ternary alloying elements such as iron in aluminium-tin alloys should be kept to the minimum compatible with the economy of the composition in order to minimize the reduction in efficiency caused by undesirable changes in the above factors.

It has been discovered that in is unique among the elements of groups IV and V of the periodic table in forming a large number of n-type defects in aluminum oxide films and thereby enabling significant changes in the galvanic conditions of the aluminum alloy.

But materials that can be distributed in the alloy as second-phase cathodes

to meet the above-mentioned requirements for highly efficient work can be chosen from a larger number of elements.

In general, a material which should be suitable for introduction as second-phase cathodes in an alloy with improved properties according to this invention should be able to be incorporated into said alloy in electrical connection with the tin-containing aluminum in said alloy without the tin's solid solubility is significantly reduced. It should preferably take the form of separated particles at the working temperatures of the anode, have high electronic conductivity and low hydrogen overvoltage,

and it should consist of a substance which is essentially less reactive with the environment than the aluminum in the aforementioned alloy, and which does not

ner surface layer with high resistance during said reaction.

As mentioned above, alloys according to the invention are unique in that they show persistent galvanic activity even if they are made on the basis of aluminium. The combination of high anodic efficiency and high galvanic currents is unique, especially when made from an aluminum alloy of essentially technical purity. Numerous uses can be made of alloys with the compositions and produced according to the processing method described here.

A large-scale application of such alloys for sacrificial anodes in the protection of metal structures surrounded by seawater. Alloys with substantially technically pure aluminum as the base metal with high galvanic yields and high anode effects suitable for use in aluminum sacrificial anodes, as well as for use in anodes in seawater cells, should preferably have a composition of 0.1 to 0, 3% tin, up to 0.5% silicon, up to 0.1% iron, while the rest is aluminum with so

small amounts of other impurities that they are insufficient to significantly interfere with the high galvanic yield and the high anodic efficiency of said alloys.

As regards the level of contamination in galvanic alloys, it appears from the discussion of ternary alloying elements in the foregoing that numerous elements may be present in said alloys in quantities insufficient to reduce the metal's ability to produce galvanic current. The permissible concentration level for a particular impurity or ternary addition depends on the galvanic properties that the alloy must have.

It has now been discovered that in addition to the ability that the alloy according to the invention has to change with regard to galvanic characteristics by heat treatment, as will be discussed below, substantial changes in the galvanic properties can be carried out with precision and reliability by to make changes in the alloy itself.

In applications that require high anode efficiency combined with high galvanic currents, the presence of additional contaminants must be avoided where they reduce or interfere with either the high efficiency or the high current production. Contaminants such as copper and zinc, which are soluble in aluminum and which cause a contraction of the aluminum lattice, must be particularly avoided when producing alloys for use where high galvanic currents are desired.

An example can be mentioned when an ingot of aluminum containing tin and other components which would otherwise give high galvanic currents, gave a reduced current due to a content of 0.02% zinc as a contaminant. The concentrations of such elements as zinc and copper should be kept at levels below 0.02%, if one wants to "avoid significant reductions in the maximum solubility of tin in the alloy and consequent poor galvanic performance.

For applications of galvanic aluminum that require higher galvanic current combined with high anode efficiency, the presence of insoluble elements such as nickel, arsenic, antimony, cobalt and the like in low concentrations is not as critical as the presence of the soluble constituents that contract the aluminum grid. However, if the concentration of such elements increases, it leads to an undesirable reduction of anodic efficiency, as mentioned above with reference to the group of insoluble ternary addition-alloying elements.

Alloys of aluminum and tin are also useful for the sustained generation of relatively low currents with high outputs for another group of applications, such as for anodes in dry batteries.

Numerous other applications can also be made of alloys according to this invention, where one can make use of their unique ability to produce galvanic current. It can e.g. in dry batteries it would be desirable to double the electrochemical properties of zinc, and for this use one would want to draw much less current than the optimal high current that can be obtained from galvanic aluminium.

According to this invention, this can be achieved by using a lower tin content. In this respect, the galvanic current rises sharply in alloys of tin-containing high-purity aluminum when the tin content is increased in the range between 0.06 and 0.08% Sn. By using heat treatments, fairly constant current yields can be achieved over a wide composition range for tin up to approx. 0.1% tin. In order to simultaneously produce uniform corrosion of the metal body, ternary elements can be added to form inclusions of secondary cathodes as described above. An alloy suitable for producing lower currents with high power in dry batteries can be made in this way. Ternary additions such as Cd, Bi or Pb can be used for this, because they are metallic conductors, are essentially insoluble in aluminum and have a relatively low hydrogen overvoltage. Ternary additives which are to serve as a source of secondary cathode particles are considered to be essentially insoluble for this purpose, when the solubility does not exceed Oi02%.

Alternatively, one can use additive elements which can form a stable compound with aluminium, such as Fe in the form of FeAl^/ Cr as CrAl_ 7 and Mn as MnAlo,,, for this purpose. These additive elements must essentially be in accordance with the formula for secondary cathode particle additives given above, and be able to promote the uniform corrosion attributable to the secondary cathode particles.

As a further alternative, it is mentioned that it has now been discovered that alloys for use in dry batteries can be produced by adding a regulated amount of even slightly soluble elements, where these dissolved elements contract the aluminum crystal lattice and thereby serve as moderators for aluminium-tin compositions with up to 0.5% tin. Such soluble ternary additions serve as moderators in that they change the galvanic behavior of an alloy with a high galvanic current yield and high anodic efficiency, so that one obtains an alloy with a combination of good anode efficiency and reduced but stable current yields. Addition of ternary alloying elements that are particularly fortunate as curative modifiers are zinc and copper, but one can also use any other ternary element that allows a similar controlled reduction of the current yields, as long as it induces a contraction of the aluminum lattice and a reduction of the solubility of tin in aluminium. Thus, consideration has been given to the use of aluminium-tin alloys containing 1.0% zinc or 0.1% copper as moderators for use in dry batteries, and likewise those containing 0.1 to 0.3% silicon.

One can easily determine the degree of effectiveness that the addition of a given amount of a particular ternary additive has in changing the galvanic current obtainable from a galvanic aluminum alloy. This can be done by measuring the potential in a closed circuit of a galvanic reference cell containing the sample piece of aluminum as anode. The measurement of this closed circuit potential provides a quick determination of the degree of galvanic current yield that can be obtained.

High current yields suitable for such applications as sacrificial anodes or seawater cell anodes are obtained when the potential between the aluminum and steel electrodes in the galvanic reference cell is more active than -0.9 volts on the hydrogen scale. If it is found that anodes have a more active, or correspondingly less noble potential when tested as such pairs, then they are generally also more galvanically active and give higher galvanic currents, as shown in fig.

3. If, on the other hand, the potential measured for a particular sample pair i

the galvanic reference cell is nobler than -0.9 volts on the hydrogen scale, then the galvanic activity of the alloy used in the galvanic test pair is generally too limited to give optimum performance in sacrificial anodes and seawater cells.

However, many of the alloys which in sample pairs in the galvanic reference cell have potentials higher than -1.0 are suitable for "many other uses that require a lower potential in the open circuit between anode and cathode, such as sacrificial sheaths and dry batteries. All in however, many valuable applications can be made of aluminum-based alloys containing galvanically activating amounts of tin, even if the test pair potential in the galvanic reference cell is nobler than -0.9 volts.There must then be uniformly distributed in them non-reactive conducting particles which can accommodate such alloys for the highly efficient current production which can be achieved according to the invention by providing for secondary cathode particles essentially in accordance with the above equation.

As mentioned in Norwegian patent no. 116 126,

then the desirable galvanic properties in such alloys are due to

partly that they contain tin in a form which forms n-type defects in the c<y>erface layers which are formed as reaction products of said alloy with reactants in the surroundings, e.g. water and oxygen or other reactants that give aluminum oxide in the surface layer. To achieve maximum galvanic currents, a maximum of tin must be present in the form of supersaturated solid solution. In general, maximum concentration of tin in solid solution and maximum galvanic currents are achieved reproducibly and reliably by homogenization treatment.

The term "homogenization treatment" means thermal treatment of an aluminium-tin alloy so that maximum uniform distribution of tin in the alloy is achieved and workpieces with a maximum amount of tin retained in metastable solid solution are obtained. Such a treatment can be carried out by holding the alloy containing aluminum and tin at 620°C for 16 hours. Unless otherwise mentioned, the alloys that are referred to here as homogenized have undergone this treatment. In common usage, the term homogenization is used to indicate a treatment that aims to make the part of an alloy element that is in metastable solid solution in an aluminum alloy as large as possible.

One of the unique features of the invention is that ability

as these alloys have to change their galvanic properties during heat treatment. Whatever properties these materials have in the cast state, they can be changed to a large extent by heat treatment of the alloy.

There is generally little tendency for aluminium-tin alloys of lower purity to exhibit optimum galvanic properties as cast. In such alloys, the use of homogenization heat treatment to dissolve the tin is actually decisive.

In addition to the homogenizing treatment mentioned above, which aims to bring a maximum of tin into solid solution, there is also a heterogenizing treatment where it is desired to partially precipitate the dissolved tin. Terms such as "heterogenization", "heterogenized alloy" and the like refer to a treatment of an aluminium-tin alloy where tin is in metastable solution at a given concentration level, in order to lower this concentration level and transfer at least part of it dissolved tin into a different phase state. A "reference" heterogenization treatment comprises 24 hours of heating at 400°C followed by a quench in water.

Although the heterogenization can be carried out at other temperatures, e.g. 300 or 500°C, and although shorter heating times can be used (generally in inverse proportion to the heating temperature), the above combination of temperature and time is effective when it comes to removing a lot of tLnn from the solid solution, and this is the method to which reference is made under the term heterogenization as it is used in the following, when nothing else is said. There is no detectable loss of tin during the heterogenization treatment.

This heterogenization treatment acts in such a way that it negates the beneficial effects of the tin on the galvanic corrosion characteristic only up to 0.08%. At a tin content of 0.12%, the galvanic currents are only slightly reduced by this treatment, and at a content of 0.20%, no significant effect appears. These results provide further evidence of the great stability of the galvanic corrosion characteristic in the range of 0.1 to 0.2% tin and that no decomposition of the metastable solid solution will occur upon long-term storage at room temperature.

One of the advantages of aluminum tin produced in accordance with the invention using homogenization is the high degree of stability shown during aging for periods of up to one year at room temperature. No loss of galvanic activity is shown in such alloys after such long storage.

It appears from the above that a unique group of aluminum alloys and articles has been described, suitable for providing many galvanic properties by adapting the content of tin and ternary elements, as well as their heat treatment. Several alloys have now been discovered whose galvanic properties also depend on the presence of n-type defects in the surface layers of reaction product and on secondary cathodes with different requirements. These are similarly sensitive to heat treatment, and they are able to produce galvanic currents on a large scale and with high potential at low cost.

In accordance with the invention, one can in particular produce alloys and objects which can deliver useful high galvanic currents on a larger scale and with less cost per unit. produced unit of electrical energy than has been possible with any galvanically active alloy hitherto known. The low price of these galvanic aluminum alloys is due to the fact that they are made on the basis of an aluminum with essentially technical purity, and the reliability and reproducibility of the galvanic properties of the manufactured alloys, thanks to their response to heat treatment, and modifications in composition.

Claims (1)

Aluminum alloy with valuable galvanic properties, except for use for primary electric cells in accordance with Norwegian patent no. 116 126, characterized in that the alloy contains 0.04 to 0.5% tin, where the tin is present to a maximum extent in solid solution and the maximum solid solubility at room temperature is 0.1%, and possibly 0 to 0.05% silicon and 0 to 0.1% iron and as further possible constituents elements which enter into solid solution with aluminum and which expand the aluminum lattice, namely: 0 to 1.1% magnesium, 0 to 0.16% bismuth, 0 to 0.094% zirconium, 0 -to 0.02% zinc, 0 to 0.02% copper, 0 to 0.096% nickel, 0 to 0.012% arsenic, 0 to 0.045% antimony and 0 to 0.021% cobalt, the remainder of the alloy being aluminum except for occasional pollutants.