GB1568170A - Aluminium base alloys - Google Patents

Description

(54) ALUMINIUM BASE ALLOYS (71) We, SWISS ALUMINIUM LTD., a company organized under the laws of Switzerland, of Chippis (Canton of Valais), Switzerland do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement:- It is an object of the present invention to provide improved aluminium base alloys which are resistant to corrosion, and which can be used as anodes, in particular as the container of a primary cell of the "dry" type, and as an anode in a hot water heater.

Alloys according to the present invention consist of from 0.5 to 1.0% by weight zinc, from 0.5 to 1.0% by weight magnesium, less than 0.1% by weight iron, one or more of cadmium, tin and lead, in amounts ranging from 0.05 to 0.3% by weight of each of cadmium and tin and from 0.01 to 0.20% by weight of lead, balance aluminium, subject to usual impurities.

It will be seen that one essential feature of these alloys is that they contain less than 0.1% by weight of iron. Aluminium base alloys containing very much less than 0.1% by weight of iron are, however, impractical from a commercial cost standpoint. On this basis, an upper limit of 0.1 /o by weight of iron in the aluminium base alloys of the present invention is considered a good compromise between the cost of the alloy material and the necessary performance characteristics of the formed material.

Preferably, the alloys contain a maximum of 0.05% by weight of iron, and one or more of cadmium, tin and lead, in amounts ranging from 0.05 to 0.15% by weight for each of cadmium and tin and from 0.02 to 0.10% by weight lead, balance aluminium. The optimum zinc concentration in the alloy is approximately 1.0% by weight. The optimum magnesium concentration in the alloy is approximately 0.5% by weight. The optimum tin and cadmium concentrations in the alloy are approximately 0.1% by weight of each element. The optimum lead concentration in the alloy is approximately 0.1% by weight.

High purity aluminium may be employed in the alloys of the present invention.

It should be noted, however, that high purity aluminium is much less economical than commercially available aluminium which would generally fulfill the same requirements as would high purity aluminium. Therefore, it is preferred in the instant invention to utilize lower purity aluminium as the base aluminium of the alloy system. This aluminium, as commercially available, is generally characterised by containing from 0.001 to 0.1% by weight silicon, and from 0.001 to 0.1% by weight iron. As noted above, it is critical that the percentage of iron in the alloy system of the present invention remain less than 0.1%, preferably less than 0.05% by weight of the alloy. The lower purity aluminium may be substituted for high purity aluminium without detriment to the electrochemical characteristics of the resulting alloy.

It should be understood that the alloys of the present invention may contain, in addition to the elements described above, other impurities normally found in commercially available aluminium. These materials should, however, be limited to amounts which will not significantly affect the anodic efficiency of the alloy by forming second phase particulate cathodes and thus promoting localized corrosion of the anode.

Any suitable cathode may be employed in a dry cell utilizing an alloy of the present invention as anode. For example, the conventional amorphous carbon or graphite cathodes may be utilized. These cathodes are usually used with a conventional cathodic depolarizer such as manganese dioxide.

The various electrolytes suggested in the art for use in dry cells may be conveniently used. Aluminium chloride Is the preferred electrolyte because of the common aluminium ion. The electrolytes which have been used for zinc primary cells, ammonium chloride and zinc chloride, would be more corrosive in the aluminium cells because of the absence of the common ion.

In the accompanying drawings:- Figure 1 is a diagrammatic view, in section, illustrating a dry cell structure; Figure 2 is a broken sectional view illustrating the sealing and venting mechanism in the dry cell structure of Figure 1; and Figure 3 is a diagrammatic view, partly in section, illustrating apparatus utilized for measuring hydrogen evolution of the aluminium base alloys of the present invention and comparative alloys during galvanostatic polarization.

Referring to Figure 1, outer case 1, which forms the covering material for the dry cell, is formed from cardboard or similar material. Directly inside case 1, but spaced therefrom near the top of the cell, is sheli 2 formed from a sheet of an aluminium base alloy of the present invention, in the shape of a hollow container with a closed lower end, or base. Contacting the outside of said base, and held in a place by a crimped end of said outer case 1, is a metallic formed disc 3, which is in electrical contact with said alloy shell. The base of said shell is covered inside with a plastic insulating disc 4, and the disc is covered with a shallow polymer-coated Kraft paper cup 5. The sidewalls of shell 2 are covered on the inside with an ionpermeable fibrous separator sheet 6. The sides of the polymer-coated Kraft paper cup 5 are pressed against the bottom of said separator sheet 6 to prevent migration of cathode mix particles to the aluminium alloy shell 2, at the junction of the plastic insulating disc 4 and the separator sheet 6.

The separator sheet covered alloy shell is filled with a conventional electrolyte paste 7. This includes a cathodic depolarizer such as a mixture of manganese dioxide and acetylene carbon black. A liquid electrolyte is added to the depolarizer mixture to activate the dry cell. A carbon rod 8 is inserted in the centre of the mixture and forms the cathode current collector for the cell. A plastic disc 9 is placed over the mixture and extends outwardly to the case 1 from carbon rod 8.

The dry cell is capped with a metallic disc 10 formed so as to cover the cathode collector rod 8 and seal the dry cell at the perimeter of the shell 2 and case 1. The disc 10 is retained by a crimped upper end of the outer case 1.

The cathode rod 8 may be placed within the cell before or after addition of the electrolyte paste. In the latter case, the disc 9 may be placed over the paste before or after insertion of the rod.

Figure 2 is an enlarged view of the sealing and spacing arrangement in the dry cell illustrated in Figure 1. A space 30 is provided between the end portion of shell 2 and the end portion of case 1 to collect any hydrogen gas which may evolve from the interaction of the electrolyte paste 7 with shell 2 through the porous separator sheet 6. The disc 9 has a rim 31 which fits between the shell 2 and the outer case 1.

Any hydrogen gas evolved will pass between the shell 2 and the rim 31 at 32, and so enter the space 30.

Figure 3 illustrates the test apparatus utilized to measure the relative hydrogen evolution rates of aluminium base alloys of the present invention and comparative alloys, in a dry battery simulation, while in use with electric current being drawn and with the electric current shut off. The apparatus was also used to measure the electrode potential of the aluminium alloy specimen which was a measure of the dry cell voltage which would be available if the alloys were used as a batterv can.

The specimen 1' consisted of a square piece of the sheet material consisting of the experimental aluminium alloy. An insulated copper lead wire 2' was connected from the specimen I ' to the counter electrode terminal 3' of a potentiostat 4'. The insulated copper lead wire 2' and the edges of the specimen 1' were masked with electrically insulating lacquer, thus leaving exactly ten square centimeters of exposed alloy material.

The specimen 1' was gripped in a groove formed in a rubber stopper 5' placed at the bottom of a glass petri dish 6'. A platinum mesh cathode 7' was inserted in the petri dish so that the mesh surrounded the specimen 1'. This cathode was connected to the reference terminal 8' of the potentiostat 4'. The petri dish was filled with a 12.5% aluminum chloride mixture 9' so that the specimen 1' was submerged 1.5 inches below the mixture surface. Saturated Calomel (Hg2CI2) 10' was placed inside a glass separatory funnel 11 which in turn was connected to a capillary tube 12 positioned within one-sixteenth of an inch from the specimen surface. A glass stopper 13, placed between the separatory funnel 11 and the capillary tube 12, was lubricated by means of a slurry of agar mixed with sodium chloride and bentonite which was capable of conducting electricity. A 17 ohm (Q) resistance was placed between the reference 8' and working 14 terminals of the potentiostat 4'. A gas burette 15 with a glass funnel fused to its bottom portion was placed over the specimen. Air was pumped out of the gas burette until the liquid 9' from the petri dish filled the entire burette. At this point, the stopper 16 on the top portion of the burette was closed. The Calomel shielded electrode lead wire 17 was connected to the positive side of an electrometer equipped with a coaxial lead wire.

The grounded shield of this coaxial lead wire was connected to the lead wire 2' between specimen 1' and counter terminal 3'.

The alloys of the present invention may be cast according to any convenient procedure, including DC and Durville casting. The cast alloys are homogenized for 4 to 30 hours at 1050--11250F (565.6--6000C), preferably for 24 hours at 1100"F (593.3"C). The homogenized alloys are then rapidly cooled, preferably with water.

The cooled alloys are scalped down to a reasonable working size and are subsequently hot worked at 850 to 10000F (454.4 to 537.80C) with a reduction of approximately 20% during each pass through the hot working station down to approximately 0.2 inch. The hot worked alloys are then cold worked with a reduction of approximately 20% during each pass through the cold working station down to a roximately 0.1 inch.

'The alloys are then annealed for 5 to 30 minutes at 750 to 1050"F (398.9 to 565.60C), preferably 15 minutes at 9500F (510"C). The annealed alloys are then finally cold worked down to the desired working thickness, preferably approximately 0.02 inch.

After being cold worked down to the final desired working thickness, the alloys are subjected to a final anneal. The alloys are finally annealed for I to 25 minutes at 100 to 8000F (37.8 to 426.7"C).

It should be noted that both the hot working and cold working steps may be repeated a number of times to reduce the alloys to desired working thicknesses in each step.

EXAMPLE I.

An alloy of 1.0% by weight zinc, 0.5% by weight magnesium and 0.1% by weight cadmium and balance aluminum was cast. The cast alloy was subjected to a 24 hour homogenization treatment at 11000F followed by water cooling. The cast ingots were scalped to 2.5 inches equally on both sides of the ingots. The scalped ingots were hot rolled at 9000F in 20% passes down to 0.2 inch. The hot rolled material was then cold rolled in 20% passes down to 0.1 inch. The cold rolled material was annealed for 15 minutes at a furnace temperature of 950" F followed by cold rolling down to 0.02 inch. The worked material was divided into three portions for testing. The first portion was finally annealed for 15 minutes at 1500 F. The second portion was finally annealed for 15 minutes at 6000F. The third portion was finally annealed for 5 minutes at 7000F Data representing the hydrogen gas evolved from samples of each annealed portion were obtained from operation of the apparatus described in Figure 3. The results are presented in Table I.

TABLE I Hydrogen Evolution from Different Anneals Hydrogen Evolution, cc per 10 cm2 Casting Party at Three Hours With One Hour With Portion Anneal Current On Current Off First 1500F x 15 min. 15.4 0.3 Second 6000F x 15 min. 16.3 0.3 Third 7000F x 5 min. 14.2 1.2 The data indicate that the 1.0% by weight zinc, 0.5% by weight magnesium and 0.1 by weight cadmium alloy can be given a partial anneal at 1500F for 15 minutes without suffering an increase of hydrogen evolution with current on compared to the material annealed at 6000F for 15 minutes. There is, however, an increase in hydrogen evolution in the current on condition relative to the material annealed for 5 minutes at 700"F.

EXAMPLE II.

An alloy containing 1.0% by weight zinc, 0.1% by weight tin, 0.5% by weight magnesium, balance aluminium, was formed into a sacrificial anode for a hot water heater. The performance of this alloy, whose range of elements falls within the range presented by the alloy system utilized in the present invention, was compared to the performance of an anode formed from Aluminium Association Alloy 8020 (0.06% Si max., 0.10% Fe max., 0.16-0.22% Sn, 0.10-0.20% Bi, 0.003-0.01 B, 0.01% Ga min., 0.03% Mg max., 0.004% Ti max., max of 0.005% for each of Cu, Mg, Cr, Ni and Zn). Both anodes were placed in hot water heaters containing water at a temperature held within 110"F + 50 throughout a two week experiment. The hot water heaters provided approximately 100 gallons of hot water daily throughout the two week test. This amount of hot water is considered normal for an average family. The weight loss of each anode was measured as well as the total coulombic output of each anode and an efficiency for each anode was measured according to the coulombic output for each loss. The results of each anode are shown in Table II.

TABLE II Coulombic Output Efficiency Comparison of Aluminium Alloy Anodes in Hot Water Weight Loss Average Current Total Coulombic Current, Density, Output Output Theoretical Anode gms. lbs. ma ma/in. amp-secs. amp-hrs/lb. Efficiency % AA 80 20 3.30 7.26 x 10-3 15.8 0.21 19,112 730 54 Al-1% Zn- 0.948 2.09 x 10-3 5.8 0.12 7,039 939 70 0.1% Sn0.5% Mg (Nominal) As can clearly be seen from Table II, the anode of the present invention demonstrates superior efficiency and resistance to weight loss compared to material normally used for this purpose.

EXAMPLE III.

The anode material containing elements within the ranges utilized in the present invention could not be directly compared to an alloy used commercially as anode material which contains 4.5% by weight zinc, 0.14% by weight tin, 0.11% by weight iron, balance aluminium. Therefore, a comparison was made between AA Alloy 8020 and this commercially available material. Both anodes were subjected to a 48 hour immersion in a 0.1M NaCl solution at 25 C # 2 . As in Example IV, the weight loss, total coulombic output and theoretical efficiency based upon output per unit of weight loss were measured for each anode. The results are shown in Table II.

TABLE III Coulombic Output Efficiency Comparison of Aluminium Alloy Anodes in 0.1M NaCl Solution Weight Loss Average Current Total Coulombic Current, Density Output Output Theoretical Anode gms. lbs. ma ma/in. amp-secs. amp-hrs/lb. Efficiency % AA 8020 0.21 4.5 x 10-4 8.60 5.60 1,496 924 68 Al-4.5% Zn- 0.024 5.3 x 10-5 0.62 0.40 104 570 42 0.14% Sn0.11% Fe The results shown in Table III allow an indirect comparison to be made between Al-1.0% Zn-0.1% Sn-0.5% Mg from Example II and Al-4.5% Zn0.14% Sn.l 1% Fe from Example III insofar as theoretical efficiency of each can be determined. As can clearly be seen from Table III, and a review of Table II, the anode within the ranges of the present invention is even more superior to the commercially available alloy of Example III than it is to AA Alloy 8020.

Therefore, the anodes of the present invention will provide greater significant protection, even in aggressive waters (i.e. those containing solid or other corrosive materials), in comparison with commercial anodes presently utilized for the same purpose.

Claims (22)

WHAT WE CLAIM IS:

1. An aluminium base alloy which is resistant to corrosion, said alloy consisting of from 0.5 to 1.0% by weight zinc, from 0.5 to 1.0% by weight magnesium, less than 0.1% by weight iron, one or more of cadmium, tin and lead, in amounts ranging from 0.05 to 0.3% by weight of each of cadmium and tin and from 0.01 to 0.20% by weight of lead, balance aluminium, subject to usual impurities.

2. An alloy according to claim 1, containing from 0.001 to 0.1% by weight iron.

3. An alloy according to claim 1 or claim 2, containing less than 0.05% by weight iron.

4. An alloy according to any of claims 1 to 3, containing up to 0.1% by weight silicon as an impurity.

5. An alloy according to claim 4, containing from 0.001 to 0.1% by weight silicon.

6. An alloy according to any of claims 1 to 5, wherein the cadmium, or tin, or both are present in amounts ranging from 0.05 to 0.15% by weight for each element.

7. An alloy according to any of claims 1 to 6, wherein the lead is present in an amount ranging from 0.02 to 0.10% by weight.

8. A method of preparing an aluminium base alloy sheet which is resistant to corrosion comprising the steps of: (a) casting an alloy according to any of claims r to 7, (b) homogenizing said cast alloy for 4 to 30 hours at 1050-1 1250F; (c) rapidly cooling said homogenized alloy; (d) hot working the quenched alloy at 850 to 10000F with a reduction of approximately 20% during each pass through the hot working station; (e) cold working the alloy with a reduction of approximately 20% during each pass through the cold working station; (f) annealing the cold worked alloy for 5 to 30 minutes at 750 to 10500 F; (g) cold working said alloy down to the final desired working thickness; and (h) annealing said cold worked alloy for 1 to 25 minutes at 100 to 8000F.

9. A method according to claim 8, wherein said hot working is performed in step (d) in at least two passes.

10. A method according to claim 8 or claim 9, wherein said cold working is performed in steps (e) and (g) in at least two passes.

11. A method according to any of claims 8 to 10, wherein said cooling is with water.

12. A method according to any of claims 8 to 11, wherein the hot working of step (d) is performed to reduce the thickness of said alloy down to approximately 0.2 inch.

13. A method according to any of claims 8 to 12, wherein the cold working of step (e) is performed to reduce the thickness of said alloy down to approximately 0.1 inch.

14. A method according to any of claims 8 to 13, wherein the cold working of step (g) is performed to reduce the thickness of said alloy down to approximately 0.02 inch.

15. A primary electric cell containing a cathode, an electrolyte, and a container as the anode for the cell, the container being of an alloy according to any of claims I to 7.

16. A primary electric cell according to claim 15, which is of the dry type and further contains a cathodic depolarizer.

17. A method of making a primary electric cell comprising the steps of: (a) forming an alloy according to any of claims 1 to 7, into a sheet; (b) forming said sheet into a hollow container having a closed end and an opposite open end; (c) placing a first inert insulating disc within said container so that the disc contacts the interior of said closed end; (d) placing an inert, semi-permeable, porous separator layer within said container so that the separator layer contacts a major portion of the interior of the hollow container; (e) forming a polymer-coated shallow paper cup against said insulating disc so that the sides of said cup press against said separator layer; (f) placing an electrolyte paste within said container so that the said separator layer is substantially covered by said paste; (g) placing a cathode rod within said electrolyte paste so that the cathode rodis prevented from contacting said separator layer by a layer of electrolyte paste and so that one end of the cathode rod within said paste projects above the open end of said container; (h) forcing a second inert insulating disc over the projecting end of said cathode rod and contacting said electrolyte paste with said disc; (i) placing metal caps over said end of the cathode rod projecting above the open end of said container and against the outer wall of the closed end of said container; and (j) covering the exterior sidewalls of said container with a sheet of cardboard or similar material, said sheet crimped over each end of said container so that said metal caps are held in place along the perimeter of each cap.

18. A method according to claim 17, wherein saidcathode rod is placed within said container before the addition of said electrolyte paste.

19. A method according to claim 17, wherein said second inert insulating disc is placed over the said electrolyte paste before said cathode rod is inserted within said paste.

20. An anode formed from an alloy according to any of claims I to 7.

21. An electrical apparatus including an anode according to claim 20.

22. A primary cell according to claim 15, substantially as described with reference to Figures 1 and 2 of the accompanying drawings.